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DESCRIPTION JP2014111529

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DESCRIPTION JP2014111529
Abstract: To provide a lead-free piezoelectric ceramic composition or the like which is excellent
in piezoelectric characteristics and does not have rapid characteristic fluctuation between -50 °
C and + 150 ° C. A lead-free piezoelectric ceramic composition comprises a first crystal phase
comprising a niobium / tantalate alkali type perovskite oxide having piezoelectric characteristics,
an A-Ti-B-O type composite oxide (element A is an alkali metal, The element B includes a second
crystal phase composed of at least one of Nb and Ta, and the contents of the element A, the
element B and the Ti are not all zero. The second crystal phase is represented by, for example, a
composition formula ATiBO. It is preferable that x satisfies 0 ≦ x ≦ 0.15. [Selected figure] Figure
4
Lead-free piezoelectric ceramic composition, piezoelectric element using the same, knock sensor,
and method for producing lead-free piezoelectric ceramic composition
[0001]
The present invention relates to a lead-free piezoelectric ceramic composition used for a
piezoelectric element or the like and a method of manufacturing the same.
[0002]
Most of the piezoelectric ceramics (piezoelectric ceramics) that have been mass-produced
conventionally are made of PZT-based (lead zirconate titanate) materials, and contain lead.
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However, in recent years, development of lead-free piezoelectric ceramic is desired to eliminate
the adverse effect of lead on the environment. As a material of such a lead-free piezoelectric
ceramic (referred to as a “lead-free piezoelectric ceramic composition”), a composition formula
ANbO3 (A is an alkali metal) such as potassium sodium niobate ((K, Na) NbO 3) Compositions
have been proposed. However, the ANbO3-based lead-free piezoelectric ceramic composition
itself has the problem of being inferior in sinterability and moisture resistance.
[0003]
In order to address such problems, in Patent Document 1 below, there is a method of improving
sinterability and improving piezoelectric characteristics by adding Cu, Li, Ta, etc. to an ANbO 3 based lead-free piezoelectric ceramic composition. It is disclosed.
[0004]
In Patent Document 2, a lead-free piezoelectric ceramic composition represented by a general
formula {Lix (K1-yNay) 1-x} (Nb1-zSbz) O3 (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1. It is disclosed that
relatively good sinterability and piezoelectric properties can be achieved by 0, 0 ≦ z, 0.2, except
x = z = 0).
[0005]
JP 2000-313664 JP JP 2003-342069
[0006]
However, in the piezoelectric ceramic composition described in Patent Document 1, although the
sinterability is improved, the piezoelectric characteristics are inferior to conventional leaded
piezoelectric ceramic compositions, and the practicability is insufficient. .
On the other hand, although the piezoelectric ceramic composition described in Patent Document
2 exhibits a relatively high piezoelectric constant, since there is a phase transition point between
-50 ° C and + 150 ° C, it is abrupt before and after this phase transition point. There was a
problem that the characteristic fluctuated.
[0007]
The present invention is a lead-free piezoelectric ceramic composition excellent in piezoelectric
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characteristics and having no rapid characteristic fluctuation between -50 ° C. and + 150 ° C.,
a piezoelectric element using the same, and a lead-free piezoelectric ceramic composition The
purpose is to provide a method of manufacturing an object.
[0008]
The present invention has been made to solve at least a part of the above-described problems,
and can be realized as the following modes or application examples.
[0009]
[Application Example 1] A lead-free piezoelectric ceramic composition comprising: a first crystal
phase consisting of a niobium / tantalate alkali perovskite oxide having piezoelectric
characteristics; A-Ti-B-O complex oxide (element A is An alkali metal, element B, and a second
crystal phase composed of at least one of Nb and Ta, and the contents of element A, element B,
and Ti are not all zero); Lead-free piezoelectric ceramic composition.
According to this configuration, the lead-free piezoelectric ceramic composition is superior in
piezoelectric characteristics to the composition composed of only the first crystal phase, and
does not have rapid characteristic fluctuation between -50 ° C and + 150 ° C. Can provide the
goods.
[0010]
Application Example 2 The lead-free piezoelectric ceramic composition according to Application
Example 1, wherein the second crystal phase is a crystal phase represented by A1-xTi1-xB1 +
xO5, and a crystal phase represented by A1Ti3B1O9. A lead-free piezoelectric ceramic
composition comprising at least one of the following.
According to this configuration, since these second crystal phases have excellent piezoelectric
characteristics, they are excellent in piezoelectric characteristics, and lead-free piezoelectric
having no rapid characteristic fluctuation between -50 ° C and + 150 ° C. A porcelain
composition can be provided.
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[0011]
Application Example 3 The lead-free piezoelectric ceramic composition as described in
Application Example 2, wherein the second crystal phase is a crystal phase represented by A1-x
Ti1-x B1 + x O5. object.
According to this configuration, the lead-free piezoelectric ceramic composition is superior in
piezoelectric characteristics to the composition composed of only the first crystal phase, and
does not have rapid characteristic fluctuation between -50 ° C and + 150 ° C. Can provide the
goods.
[0012]
Application Example 4 The lead-free piezoelectric ceramic composition according to Application
Example 3, wherein x satisfies 0 ≦ x ≦ 0.15.
In this configuration, excellent piezoelectric characteristics can be obtained as the whole leadfree piezoelectric ceramic composition. In this configuration, since the second crystal phase
becomes stable, a stable composition can be provided as the whole lead-free piezoelectric
ceramic composition, and in addition, the insulation properties of the lead-free piezoelectric
ceramic composition can also be improved. it can.
[0013]
Application Example 5 The lead-free piezoelectric ceramic composition according to Application
Example 4, wherein the element A is K. In this configuration, it is possible to obtain a
composition inexpensive and excellent in piezoelectric characteristics.
[0014]
Application Example 6 The lead-free piezoelectric ceramic composition according to Application
Example 4, wherein the element A is Cs, and the x satisfies 0 ≦ x ≦ 0.1. Composition. In this
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configuration, since the second crystal phase is more stable, excellent piezoelectric
characteristics can be obtained as a whole of the lead-free piezoelectric ceramic composition in
this configuration. A more stable composition can be provided as the whole lead-free
piezoelectric ceramic composition, and additionally, the insulation of the lead-free piezoelectric
ceramic composition can be improved.
[0015]
Application Example 7 The lead-free piezoelectric ceramic composition according to any one of
Application Examples 1 to 6, wherein the element B is Nb. In this configuration, a composition
that is inexpensive and has excellent heat resistance can be obtained. In addition, a composition
having a higher Curie temperature (Tc) can be obtained as compared to the case where the
element B is Ta.
[0016]
Application Example 8 The lead-free piezoelectric ceramic composition according to any one of
Application Examples 1 to 7, wherein the content ratio of the second crystal phase is more than 0
mol% and 15 mol% or less. Lead-free piezoelectric ceramic composition characterized by the
above. In this configuration, a lead-free piezoelectric ceramic composition having a high
piezoelectric constant can be obtained.
[0017]
Application Example 9 The lead-free piezoelectric ceramic composition according to any one of
Application Examples 1 to 8, wherein the niobium / tantalate alkali type perovskite oxide forming
the first crystal phase is an alkaline earth metal. A lead-free piezoelectric ceramic composition
comprising: Even with this configuration, a composition having excellent piezoelectric
characteristics can be obtained.
[0018]
Application Example 10 The lead-free piezoelectric ceramic composition described in Application
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Example 9, wherein the niobium / tantalate alkali type perovskite oxide forming the first crystal
phase has a compositional formula (KaNabLicCd) eDof (element C is alkali) Element D is at least
one of Nb and Ta, a, b, c and d satisfy a + b + c + d = 1, and e and f are arbitrary) A lead-free
piezoelectric ceramic composition characterized by being represented by The lead-free
piezoelectric ceramic composition containing the first crystal phase and the second crystal phase
exhibits excellent insulation and piezoelectric properties.
[0019]
Application Example 11 The lead-free piezoelectric ceramic composition described in Application
Example 10, wherein the e satisfies 0.97 ≦ e ≦ 1.08. In this configuration, it is possible to
obtain a lead-free piezoelectric ceramic composition having further excellent piezoelectric
characteristics.
[0020]
Application Example 12 The lead-free piezoelectric ceramic composition according to any one of
Application Examples 1 to 11, further comprising Cu, Ni, Co, Fe, Mn, Cr, Zr, Ag, Zn, Sc, Bi. A leadfree piezoelectric ceramic composition containing at least one metal element of Also in this case,
a lead-free piezoelectric ceramic composition having excellent piezoelectric properties can be
obtained.
[0021]
Application Example 13 A piezoelectric element comprising: a piezoelectric ceramic formed of
the lead-free piezoelectric ceramic composition according to any one of Application Examples 1
to 12; and an electrode attached to the piezoelectric ceramic. .
[0022]
[Example 14 of application] A knock sensor provided with the piezoelectric element according to
example 13 of application.
[0023]
Application Example 15 An ultrasonic transducer comprising the piezoelectric element described
in Application Example 13.
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[0024]
[Example 16 of application] A cutting tool provided with the piezoelectric element according to
example 13 of application.
[0025]
Application Example 17 In the method of manufacturing the lead-free piezoelectric ceramic
composition according to any one of Application Examples 1 to 12, the raw materials of the first
crystal phase are mixed and calcined to obtain a first powder. A step of preparing, a step of
mixing the raw material of the second crystal phase, and calcinating to form a second powder,
mixing the first and second powders, forming, and firing, Producing the lead-free piezoelectric
ceramic composition. The method for producing a lead-free piezoelectric ceramic composition,
comprising:
According to this manufacturing method, since the first crystal phase and the second crystal
phase are separately generated, the respective compositions can be more strictly managed.
As a result, the yield of the lead-free piezoelectric ceramic composition can be improved.
[0026]
6 is a flowchart showing a method of manufacturing a piezoelectric element in an embodiment of
the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the piezoelectric
element as one Embodiment of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the knock sensor as
one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The longitudinal
cross-sectional view which shows the ultrasonic transducer | vibrator as one Embodiment of this
invention. BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the
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cutting tool as one Embodiment of this invention. The figure which shows the experimental result
regarding the influence on the characteristic of the piezoelectric ceramic composition by a
subphase ratio etc. FIG. The graph which shows the experimental result regarding the influence
on the piezoelectric constant of the piezoelectric ceramic composition by a subphase ratio. The
figure which shows the experimental result regarding the influence on transition temperature by
a subphase ratio etc. FIG. The figure which shows the experimental result regarding the influence
on the characteristic of the piezoelectric ceramic composition by the coefficient e of matrix phase
composition formula. The graph which shows the experimental result regarding the influence to
the piezoelectric constant of the piezoelectric ceramic composition by the coefficient e of matrix
phase composition formula. The figure which shows the experimental result regarding the
influence on the characteristic of the piezoelectric ceramic composition by an addition metal. The
figure which shows the experimental result regarding the influence on the insulation of the
piezoelectric ceramic composition by the presence or absence of a subphase. The figure which
shows the analysis result of the 2nd crystal phase in the piezoelectric ceramic composition at the
time of mixing a subphase as a KTiNbO5 phase. The figure which shows the analysis result of the
2nd crystal phase in the piezoelectric ceramic composition at the time of mixing a subphase as a
KTi3NbO9 phase. The figure which shows the other experimental result regarding the influence
on the characteristic of the piezoelectric ceramic composition by an addition metal. The figure
which shows the heat cycle evaluation test result of a piezoelectric ceramic composition.
[0027]
A piezoelectric ceramic composition according to an embodiment of the present invention is a
lead-free piezoelectric including a first crystal phase consisting of a niobium / tantalate alkali
perovskite oxide having piezoelectric properties and a second crystal phase not having
piezoelectric properties. It is a porcelain composition. In a typical lead-free piezoelectric ceramic
composition according to one embodiment, the proportion of the second crystal phase is more
than 0 mol% and less than 20 mol%, and the balance is the first crystal phase. Hereinafter, the
first crystal phase is also referred to as "mother phase", and the second crystal phase is also
referred to as "subphase". In a typical example, the second crystal phase is a layered structure
compound (or layered compound), and by being mixed with the first crystal phase, the
sinterability is improved and, in addition, the insulation property is also improved. In addition, it
has the function of stabilizing the crystal structure of the first crystal phase so as not to cause an
abrupt change in properties due to the phase transition point between -50 ° C and + 150 ° C.
[0028]
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As the perovskite oxide forming the first crystal phase, it is preferable to use an alkali niobate
perovskite oxide or an alkali tantalate perovskite oxide. The term "niobium / tantalate alkali
perovskite oxide" is a generic term for these two types of perovskite oxides. The alkali-based
component of the niobium / tantalate alkali-based perovskite oxide contains at least an alkali
metal (Li, Na, K, etc.), and an alkaline earth metal (Ca (calcium), Sr (strontium), Ba (barium) Etc.).
As such niobium / tantalate alkali type perovskite oxides, those represented by the following
composition formula are preferable.
[0029]
<Compositional Formula of Preferred First Crystal Phase> (KaNabLicCd) eDof Here, the element C
is at least one of the alkaline earth metals Ca (calcium), Sr (strontium) and Ba (barium), and the
element D is At least one of Nb (niobium) and Ta (tantalum), a, b, c, and d satisfy a + b + c + d = 1,
and e and f have arbitrary values.
[0030]
In the above composition formula, K (potassium), Na (sodium), Li (lithium) and the element C (Ca,
Sr, Ba) are disposed at the so-called A site of the perovskite structure, and the element D (Nb, Ta)
is the so-called It is placed at the B site.
That is, the niobium / tantalate alkali type perovskite oxide may contain at least one of alkali
metals (K, Na, Li) at its A site and may contain alkaline earth metals (Ca, Sr, Ba). Also, it is a
perovskite oxide containing at least one of Nb (niobium) and Ta (tantalum) at its B site.
[0031]
As a value of the coefficients a to f in the above composition formula, a preferable value is
selected from the viewpoint of the electrical characteristics or piezoelectric characteristics (in
particular, the piezoelectric constant d33) of the lead-free piezoelectric ceramic composition
among combinations of values for forming the perovskite structure. Be done. Specifically, the
coefficients a to d satisfy 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, respectively, but a = b =
c = 0 (that is, K Compositions which do not contain (potassium), Na (sodium) and Li (lithium) are
excluded. The coefficients a and b of K (potassium) and Na (sodium) are typically 0 <a ≦ 0.6, 0
<b ≦ 0.6. The coefficient c of Li (lithium) may be zero, but 0 <c ≦ 0.2 is preferable, and 0 <c ≦
0.1 is more preferable. Although the coefficient d of the element C (Ca, Sr, Ba) may be zero, 0 <d
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≦ 0.1 is preferable, and 0 <d ≦ 0.05 is more preferable. The coefficient e for the entire A site is
arbitrary, but typically 0.9 ≦ e ≦ 1.1, preferably 0.97 ≦ e ≦ 1.08, and 1.00 ≦ e ≦ 1.08. Is
particularly preferred.
[0032]
In the above composition formula, the valence of K, Na, Li is +1, the valence of the element C (Ca,
Sr, Ba) is +2, and the valence of the element D (Nb, Ta) is +5, The valence of O (oxygen) is +2. The
factor f takes any value such that the first crystal phase constitutes a perovskite oxide, and a
typical value for the factor f is about 3. From the electrical neutralization conditions of the
composition, the coefficients a to f can be expressed by the following equation (1).
[0033]
(a+b+c+2×d)×e+5 ≒ 2×f …(1)
[0034]
The typical composition of the first crystal phase is (K, Na, Li, Ca) 1.07 NbO 3.06 (coefficients a
to d are omitted).
Since this first crystal phase contains K (potassium), Na (sodium) and Nb (niobium) as main metal
components, the material composed of the first crystal phase is also referred to as "KNN" or "KNN
material". Call. If Ca (calcium) is selected as the element C and Nb (niobium) is selected as the
element D as in this example, it is possible to obtain a piezoelectric ceramic composition
inexpensive and excellent in characteristics.
[0035]
As the second crystal phase, one represented by the following composition formula is preferable.
<Composition Formula of Preferred Second Crystal Phase> A1-x Ti1-x B1 + x O5 Here, the
element A is at least one of alkali metals (K (potassium), Rb (rubidium), Cs (cesium), etc.) and The
element B is at least one of Nb (niobium) and Ta (tantalum), and x is an arbitrary value. However,
it is preferable that the coefficient x satisfy 0 ≦ x ≦ 0.15. If the coefficient x takes a value in this
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range, the structure of the second crystal phase is stable, and a uniform crystal phase can be
obtained.
[0036]
Specific examples of the second crystal phase according to the above composition formula
include KTiNbO5, K0.90 Ti0.90 Nb1.10 O5, K0.85 Ti0.85 Nb1.15 O5, Rb TiNb O5, Rb 0.90 Ti
0.90 Nb1. 15O5, CsTiNbO5, Cs0.90Ti0.90 Nb1.10O5, KTiTaO5, and CsTiTaO5 can be used. From
the viewpoint of structural stability of the second crystal phase, the coefficient x preferably
satisfies 0 ≦ x ≦ 0.15 when the element A is K (potassium) or Rb (rubidium), When A is Cs
(cesium), it is preferable to satisfy 0 ≦ x ≦ 0.10. If K (potassium) is selected as the element A
and Nb (niobium) is selected as the element B, it is possible to obtain a piezoelectric ceramic
composition inexpensive and excellent in characteristics.
[0037]
The second crystal phase does not have a piezoelectric property, but when it is mixed with the
first crystal phase, the sinterability is improved and, in addition, the insulation property is also
improved. It also seems to contribute to the function of preventing a phase transition point from
occurring between -50 ° C and + 150 ° C. The second crystal phase is a layered structure
compound (or layered compound), and the point of being a layered structure compound
contributes to the improvement of the insulation property of the piezoelectric ceramic
composition and the function of preventing generation of a phase transition point It is estimated
to be. The point that the second crystal phase has a stable structure is disclosed in H. Rebbah et
al., Journal of Solid State Chemistry, Vol. 31, p. 321-328, 1980, the entire disclosure of which is
incorporated herein by reference. Is incorporated herein by reference.
[0038]
The content ratio of the second crystal phase may be more than 0 mol% and less than 20 mol%,
but is preferably more than 0 mol% and 15 mol% or less. The composition which does not
contain the second crystal phase (composition of only the first crystal phase) tends to show a
sharp characteristic fluctuation between -50 ° C and + 150 ° C. If the content ratio of the
second crystal phase exceeds 15 mol%, the piezoelectric characteristics (particularly, the
piezoelectric constant d33) may be reduced.
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[0039]
The typical composition of the second crystal phase is K0.85Ti0.85Nb1.15O5. Since this second
crystal phase contains Nb (niobium), Ti (titanium) and K (potassium) as the main metal
components, the material composed of the second crystal phase can be either "NTK" or "NTK
material". Call.
[0040]
As a preferable second crystal phase, in addition to the crystal phase represented by A1-xTi1-xB1
+ xO5 described above, a crystal phase represented by A1Ti3B1O9 can also be used. Although
the coefficient 1 is usually omitted normally, in the present specification, in order to clarify the
difference from the crystal phase represented by A1-xTi1-xB1 + xO5 described above, this is
intentionally used. The factor 1 may be described. In the following, the crystal phase represented
by A1-xTi1-xB1 + xO5 is also referred to as "NTK1115 phase" or simply "1115 phase", and the
crystal phase represented by A1Ti3B1O9 is "NTK 1319 phase" or simply "1319 phase". Also
called
[0041]
Also in the crystal phase represented by A1Ti3B1O9, the element A is at least one of alkali metals
(K (potassium), Rb (rubidium), Cs (cesium), etc.), and the element B is Nb (niobium) and Ta. At
least one of (tantalum). The second crystal phase represented by A1Ti3B1O9 also has no
piezoelectric property, but when it is mixed with the first crystal phase, the sinterability is
improved and, in addition, the insulation property is also improved. It also seems to contribute to
the function of preventing a phase transition point from occurring between -50 ° C and + 150
° C.
[0042]
The content ratio of the second crystal phase represented by A1Ti3B1O9 may also be more than
0 mol% and less than 20 mol%, but is preferably more than 0 mol% and 15 mol% or less. The
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composition which does not contain the second crystal phase (composition of only the first
crystal phase) tends to show a sharp characteristic fluctuation between -50 ° C and + 150 ° C.
If the content ratio of the second crystal phase exceeds 15 mol%, the piezoelectric characteristics
(particularly, the piezoelectric constant d33) may be reduced.
[0043]
The crystal phase represented by A1-xTi1-xB1 + xO5 and the crystal phase represented by
A1Ti3B1O9 are both element A (alkali metal), Ti (titanium), and at least element B (Nb and Ta) It
is common in that it is a 1) complex oxide. Thus, the complex oxide of the element A, Ti
(titanium), and the element B is called "A-Ti-B-O-based complex oxide". In the present invention,
as the second crystal phase, an A-Ti-B-O complex oxide (element A is an alkali metal, element B is
at least one of Nb and Ta, element A, element B and Ti It is possible to use any content not zero).
In particular, it does not have piezoelectric properties by itself, and improves the sinterability by
being mixed with the first crystal phase, and also improves the insulating property, and also
between -50 ° C and + 150 ° C. It is preferable to use an A-Ti-B-O-based composite oxide which
does not cause a phase transition point.
[0044]
The lead-free piezoelectric ceramic composition as an embodiment of the present invention is Cu
(copper), Ni (nickel), Co (cobalt), Fe (iron), Mn (manganese), Cr (chromium), Zr (zirconium), Ag At
least one metal element of (silver), Zn (zinc), Sc (scandium), and Bi (bismuth) may be contained.
Even if these metal elements are added, it is possible to obtain a lead-free piezoelectric ceramic
composition having excellent properties (in particular, the piezoelectric constant d33). The total
value of the content ratio of these additive metals is preferably 5 mol% or less, and more
preferably 1 mol% or less. When the total value of the content ratio of the added metal exceeds 5
mol%, the piezoelectric properties may be deteriorated. In addition, when adding 2 or more types
of metals, it is preferable to make content rate per 1 type of addition metal into less than 1 mol%.
Even when the content ratio per additive metal exceeds 1 mol%, the piezoelectric characteristics
may be deteriorated.
[0045]
FIG. 1 is a flowchart showing a method of manufacturing a piezoelectric element according to an
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embodiment of the present invention. In step T110, necessary raw materials such as K2CO3
powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, SrCO3 powder, BaCO3 powder,
Nb2O5 powder, Ta2O5 powder and the like are selected as raw materials for the matrix phase
(KNN), Weigh according to the values of the coefficients a to e in the composition formula of the
phase. Then, ethanol is added to these raw material powders, and wet mixing is carried out
preferably for 15 hours or more in a ball mill to obtain a slurry. In step T120, the mixed powder
obtained by drying the slurry is calcined, for example, at 600 to 1000 ° C. in an air atmosphere
for 1 to 10 hours to generate a matrix calcined body.
[0046]
In step T130, necessary one is selected from K2CO3 powder, Rb2CO3 powder, Cs2CO3 powder,
TiO2 powder, Nb2O3 powder, Ta2O3 powder and the like, and weighed according to the value of
coefficient x in the composition formula of the subphase. Then, ethanol is added to these raw
material powders, and wet mixing is carried out preferably in a ball mill for preferably 15 hours
or more to obtain a slurry. In step T140, the mixed powder obtained by drying the slurry is
calcined, for example, at 600 to 1000 ° C. in an air atmosphere for 1 to 10 hours to form a
calcined product, thereby producing a secondary-phase calcined product.
[0047]
In step T150, the matrix-phase calcined product and the secondary-phase calcined product are
weighed, respectively, added with a dispersant, a binder and ethanol in a ball mill, and pulverized
and mixed to form a slurry. In addition, when adding an additive metal, CuO powder, Fe2O3
powder, NiO powder, Ag2O powder, ZrO2 powder, ZnO powder, ZnO powder, MgO powder,
Sc2O3 powder, Bi2O3 powder, Cr2O3 powder, MnO2 powder, CoO powder, etc. are necessary.
Select ones, weigh and mix in the slurry. The slurry may be calcined again and then crushed and
mixed. Thereafter, the slurry is dried, granulated, and uniaxially pressed, for example, at a
pressure of 20 MPa to form a desired shape. The shape of a typical piezoelectric ceramic suitable
for the composition according to the embodiment of the present invention is a disk shape or a
cylindrical shape. Thereafter, CIP processing (cold isostatic pressing processing) is performed, for
example, at a pressure of 150 MPa. And in process T160, a piezoelectric ceramic is obtained by
hold | maintaining and baking the obtained CIP press body at 900-1300 degreeC in air |
atmosphere atmosphere for 1 to 10 hours, for example. This firing may be performed in an O 2
atmosphere. In step T170, the piezoelectric ceramic is processed in accordance with the
dimensional accuracy required of the piezoelectric element. In step T180, an electrode is
attached to the piezoelectric ceramic thus obtained, and in step T190, polarization processing is
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performed.
[0048]
In addition, although an addition metal is added as a metal oxide in process T150, the preferable
content of the addition metal mentioned above is the value converted into mol% as a metal
single-piece | unit. The additive metal is not a metal oxide containing only the additive metal, but
an oxide CMO3 (element C is at least one of Ca, Sr, and Ba, and an element M is an additive
metal) containing an alkaline earth metal and an additive metal, In step T150, the first crystal
phase (mother phase) and the second crystal phase (sub phase) may be mixed. The element C
(alkaline earth metal element) contained in the oxide CMO3 as the third component is used as
the element C in the first crystal phase in the piezoelectric ceramic after firing.
[0049]
The above-described manufacturing method is an example, and various other processes and
processing conditions for manufacturing the piezoelectric element can be used. For example,
instead of mixing and firing the first and second crystal phases separately and then mixing the
two powders as shown in FIG. 1, the raw materials are prepared at a ratio according to the
composition of the final piezoelectric ceramic composition. The piezoelectric ceramic
composition may be manufactured by mixing and firing. However, according to the
manufacturing method of FIG. 1, since the compositions of the first crystal phase and the second
crystal phase can be managed more strictly, it is possible to increase the yield of the piezoelectric
ceramic composition.
[0050]
FIG. 2 is a perspective view showing a piezoelectric element according to an embodiment of the
present invention. The piezoelectric element 200 has a configuration in which electrodes 301
and 302 are attached to the upper surface and the lower surface of the disk-shaped piezoelectric
ceramic 100. In addition, the piezoelectric element of various structures other than this can be
formed as a piezoelectric element.
[0051]
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FIG. 3A is an exploded perspective view showing an example of a knock sensor using a
piezoelectric ceramic according to an embodiment of the present invention. The knock sensor 1
is a so-called non-resonance type knock sensor, and includes the metal shell 2, the insulating
sleeve 3, the insulating plates 4 and 5, the piezoelectric element 6, the weight 7 for characteristic
adjustment, the washer 8 and the nut 9. And a housing 10. The metal shell 2 is constituted by a
cylindrical cylindrical body 2b having a through hole 2a formed therethrough and a toroidal discshaped seat surface portion 2c projecting like a flange from the lower end portion peripheral
edge of the cylindrical body 2b. ing. Further, a screw thread 2d is engraved on the upper portion
of the cylindrical body 2b, and a groove 2e for enhancing the adhesion with the housing 10 is
surrounded on the outer periphery at the upper end portion of the cylindrical body 2b and the
peripheral portion of the seat surface portion 2c. It is engraved on the In addition, each part 2a2d of the metal shell 2 is integrally formed using an appropriate manufacturing method (casting,
forging, shaving process, etc.). Further, plating (zinc chromate plating or the like) is applied to the
surface of the metal shell 2 in order to improve the corrosion resistance.
[0052]
The insulating sleeve 3 has a thin-walled cylindrical shape and is formed of an insulating material
(various plastic materials such as PET and PBT, a rubber material, and the like). Each of the
insulating plates 4 and 5 has a thin donut-like disc shape, and is formed of an insulating material
(various plastic materials such as PET and PBT, a rubber material, and the like). The piezoelectric
element 6 as a vibration detecting means has a piezoelectric ceramic 6c laminated between two
thin plate electrodes 6a and 6b, and forms a doughnut-shaped disc as a whole.
[0053]
The characteristic adjustment weight 7 has a doughnut-like disc shape, and is formed of a
material having a predetermined density (various metal materials such as brass). The insulating
sleeve 3 is fitted to the cylindrical body 2b of the metal shell 2, and the insulating plate 4, the
piezoelectric element 6, the insulating plate 5, and the weight 7 for characteristic adjustment are
fitted to the insulating sleeve 3 in this order. Further, a nut 9 is screwed into a thread 2 d of the
cylindrical body 2 b of the metal shell 2 via a washer 8. The insulating plate 4, the piezoelectric
element 6, the insulating plate 5, the weight 7 for characteristic adjustment, and the washer 8
are respectively sandwiched and fixed between the upper surface of the seat portion 2 c of the
metal shell 2 and the nut 9. A housing 10 is formed of an insulating material (various plastic
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materials such as PA) which is injection-molded to cover 8. Therefore, only the lower surface of
the seating surface portion 2c of the metal shell 2 is exposed from the lower end portion of the
housing 10, and only the upper end of the cylindrical body 2b of the metal shell 2 is exposed
from the upper end portion of the housing 10. Further, the piezoelectric element 6 is surrounded
by the insulating sleeve 3, the insulating plates 4 and 5, and the housing 10, and the metal shell
2 and the weight 7 for characteristic adjustment and the piezoelectric element 6 are insulated.
Lead wires (not shown) are connected to the electrodes 6 a and 6 b of the piezoelectric element
6, and the lead wires are led out of the housing 10.
[0054]
Since this knock sensor 1 is configured using the piezoelectric element 6 which is excellent in
piezoelectric characteristics and does not have a rapid characteristic fluctuation between -50 °
C. and + 150 ° C., knocking detection accuracy is high, In addition, a knock sensor excellent in
thermal durability can be realized.
[0055]
FIG. 3B is a longitudinal sectional view showing an ultrasonic transducer as an embodiment of
the present invention.
The ultrasonic transducer 20 is a Langevin type ultrasonic transducer, and comprises a
piezoelectric element pair 22, a pair of upper and lower front plates 25 sandwiching the
piezoelectric element pair 22, and a backing plate 26. The piezoelectric element pair 22 is
formed by laminating two annularly formed piezoelectric elements 23a and 23b with an
electrode plate 24a interposed therebetween, and arranging the electrode plate 24b on the upper
part of the upper annular piezoelectric element 23b. Is configured. The front plate 25 and the
backing plate 26 are made of cylindrical metal blocks formed using iron or aluminum as a
material. The piezoelectric element pair 22 is disposed between the front plate 25 and the
backing plate 26 and is integrally coupled by a central bolt 27.
[0056]
The front plate 25 and the backing plate 26 are both formed larger in diameter than the
diameters of the piezoelectric elements 23a and 23b, and the diameter of the contact end with
the piezoelectric elements 23a and 23b is reduced via the conical portions 28 and 29. Thus, the
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diameters of the piezoelectric elements 23a and 23b are substantially equal. The diameter R2 of
the backing plate 26 and the diameter R1 of the front plate 25 are set to have substantially the
same dimensions, and the outer end face of the front plate 25 is the ultrasonic radiation surface
30. Further, a blind end hole 31 having a diameter R3 along the axial direction is formed at the
central portion of the outer end surface of the backing plate 26. Then, the total length of the
ultrasonic transducer 20 having such a configuration is set to substantially match the resonance
length of the 3/2 wavelength of the predetermined resonance frequency.
[0057]
This ultrasonic transducer is configured using the piezoelectric elements 23a and 23b which are
excellent in piezoelectric characteristics and have no rapid characteristic fluctuation between 50.degree. C. and + 150.degree. An ultrasonic transducer capable of generating ultrasonic waves
and having excellent thermal durability can be realized.
[0058]
FIG. 3B is a perspective view showing a cutting tool according to an embodiment of the present
invention.
The cutting tool 40 is configured such that a grindstone portion 45 is formed on the outer
peripheral portion of a base 46 formed in a circular shape. The central portion of the base 46 is
fixed to the spindle 42 by a mounting jig 44. Annular piezoelectric elements 43 are embedded in
both surfaces of the base material 46. The vibration direction of the piezoelectric element 43 is a
radiation direction 47 from the center of the base 46 toward the outer periphery. The workpiece
can be cut by pressing the workpiece against the grindstone portion 45 provided on the outer
periphery of the base material 46 in a state where the spindle 42 is rotated in the rotational
direction 48 while the piezoelectric element 43 vibrates. It is.
[0059]
Since this cutting tool is constituted using the piezoelectric element 43 which is excellent in
piezoelectric characteristics and does not have a sharp characteristic fluctuation between -50 °
C and + 150 ° C, a cutting tool excellent in thermal durability Can be realized.
[0060]
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18
The piezoelectric ceramic composition and the piezoelectric element according to the
embodiment of the present invention can be widely used in vibration detection applications,
pressure detection applications, oscillation applications, piezoelectric device applications, and the
like.
For example, sensors (such as knock sensors and combustion pressure sensors) that detect
various types of vibration, vibrators, piezoelectric devices such as actuators and filters, high
voltage generation devices, micro power supplies, various drive devices, position control devices,
vibration suppression devices, It can be used for fluid discharge devices (paint discharge, fuel
discharge, etc.). In addition, the piezoelectric ceramic composition and the piezoelectric element
according to the embodiment of the present invention are particularly suitable for applications
where excellent thermal durability is required (for example, a knock sensor, a combustion
pressure sensor, etc.).
[0061]
FIG. 4 is a diagram showing experimental results on the characteristics of a plurality of sample
compositions including an example of the present invention. From this experimental result, it is
possible to evaluate the influence of the subphase ratio on the characteristics of the piezoelectric
ceramic composition. Further, with respect to the type of the component element B (Nb, Ta) of
the subphase and the type of the component element C (Ca, Sr, Ba) of the main phase, the
influence on the characteristics of the piezoelectric ceramic composition can be evaluated.
[0062]
Samples S01 to S04 in FIG. 4 are samples created as comparative examples. The samples S01
and S02 are composed of only the second crystal phase. In preparing these samples S01 and
S02, first, each of the K2CO3 powder, the Nb2O5 powder, and the TiO2 powder was weighed so
that the coefficient x in the composition formula of the second crystal phase becomes the
quantitative ratio shown in FIG. 4 . Then, ethanol was added to these powders and wet mixed in a
ball mill for 15 hours to obtain a slurry. Thereafter, the mixed powder obtained by drying the
slurry was calcined at 600 to 1000 ° C. for 1 to 10 hours in an air atmosphere to obtain a
calcined material. The calcined product was pulverized in a ball mill, mixed with a dispersant, a
binder and ethanol, and mixed to form a slurry. Thereafter, the slurry was dried, granulated,
subjected to uniaxial pressing at a pressure of 20 MPa, and formed into a disk shape (diameter
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19
20 mm, thickness 2 mm). Thereafter, CIP processing was performed at a pressure of 150 MPa,
and the obtained CIP pressed body was sintered while being held at 900 to 1300 ° C. in an air
atmosphere for 1 to 10 hours.
[0063]
The samples S03 and S04 are composed of only the first crystal phase. In preparing these
samples S03 and S04, first, each of K2CO3 powder, Na2CO3 powder, Li2CO3 powder and
Nb2O5 powder is subjected to each of the coefficients a, b, c, d and e in the composition formula
of the first crystal phase. Were weighed so as to obtain the quantitative ratio of FIG. Ethanol was
added to these powders and wet mixed in a ball mill for 15 hours to obtain a slurry. Thereafter,
the mixed powder obtained by drying the slurry was calcined at 600 to 1000 ° C. for 1 to 10
hours in an air atmosphere to obtain a calcined material. The calcined product was pulverized in
a ball mill, mixed with a dispersant, a binder and ethanol, and mixed to form a slurry. Thereafter,
the slurry was dried, granulated, subjected to uniaxial pressing at a pressure of 20 MPa, and
formed into a disk shape (diameter 20 mm, thickness 2 mm). Thereafter, CIP processing was
performed at a pressure of 150 MPa, and the obtained CIP pressed body was sintered while
being held at 900 to 1300 ° C. in an air atmosphere for 1 to 10 hours.
[0064]
Samples S05 to S15 are compositions containing both the first crystal phase and the second
crystal phase. These samples S05 to S15 were respectively produced according to the steps T110
to T160 of FIG. 1 described above. In addition, the shape after shaping | molding in process
T150 was made into disk shape (diameter 20 mm, thickness 2 mm).
[0065]
The processes of steps T170 to T190 in FIG. 1 were performed on these samples S01 to S15,
respectively, to create piezoelectric elements 200 (FIG. 2). For the piezoelectric element 200 of
each sample thus obtained, the electrical characteristics (relative dielectric constant ε 33 <T> /
ε 0) and piezoelectric characteristics (piezoelectric constant d 33 and electromechanical
coupling coefficient kr) of the piezoelectric ceramic 100 were measured, and FIG. The results
shown in
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20
[0066]
The samples S01 and S02 constituted only by the second crystal phase do not have piezoelectric
characteristics. Although these two samples S01 and S02 have different values of the coefficient
x of the composition formula of the second crystal phase, there is no difference between the
relative dielectric constants ε33 <T> / ε0 of the two. Therefore, even in the piezoelectric
ceramic composition containing both the first crystal phase and the second crystal phase, the
influence of the coefficient x of the composition formula of the second crystal phase on the
electrical characteristics and piezoelectric characteristics of the piezoelectric ceramic
composition It is presumed to be small. In this sense, the coefficient x may be an arbitrary value
such that a stable uniform crystal phase can be obtained as the second crystal phase.
[0067]
The samples S03 and S04 constituted only by the first crystal phase have piezoelectric
characteristics. These samples S03 and S04 are common in that they do not contain the element
C (Ca, Sr, Ba). However, while the sample S03 does not contain Li, the sample S04 is different
from the other in that the sample S04 contains Li. The element D of the first crystal phase is Nb
(niobium). The samples S03 and S04 do not have a large difference in electrical characteristics
(dielectric constant ε33 <T> / ε0) and piezoelectric characteristics (piezoelectric constant d33
and electromechanical coupling coefficient kr). However, the sample S04 containing Li is
preferable in that the piezoelectric constant d33 is slightly larger than the sample S03 not
containing Li. In consideration of this point, it is preferable that the first crystal phase contains
Li, even in the piezoelectric ceramic composition containing both the first crystal phase and the
second crystal phase.
[0068]
Sample S05 is a composition in which 5 mol% of the second crystal phase is added to the first
crystal phase. The first crystal phase does not contain the element C (Ca, Sr, Ba), and the
coefficient x of the composition formula of the second crystal phase is zero. The sample S05
corresponds to a combination of the sample S01 and the sample S04. As compared with the
characteristics of the sample S04 of only the first crystal phase, the sample S05 has extremely
large values of the relative permittivity ε33 <T> / ε0 and the piezoelectric constant d33, and
has preferable characteristics as a piezoelectric ceramic composition ing. The sample S05 is also
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21
excellent in that the electromechanical coupling coefficient kr is larger than the sample S04.
[0069]
Samples S06 to S12 are compositions in which the subphase ratio is changed from 3 mol% to 20
mol%. The composition of the first crystal phase is (K 0.421 Na 0.518 Li 0.022 Ca 0.039) 1.07
NbO 3.06. The composition of the second crystal phase is K0.85Ti0.85B1.15O5 in all cases. The
relative dielectric constants ε33 <T> / ε0 of the samples S06 to S12 are all preferable in that
they are sufficiently larger than the sample S04 of the comparative example. From the viewpoint
of relative permittivity, the subphase ratio is preferably in the range of 3 to 10 mol%, and more
preferably in the range of 3 to 6 mol%.
[0070]
The samples S06 to S11 are also preferable in that the piezoelectric constant d33 is sufficiently
larger than that of the sample S04 of the comparative example. The sample S12 having a minor
phase ratio of 20 mol% is not preferable because the piezoelectric constant d33 is smaller than
that of the sample S04 of the comparative example.
[0071]
FIG. 5 is a graph showing the change of the piezoelectric constant d33 for samples S06 to S12.
The horizontal axis is the auxiliary phase ratio, and the vertical axis is the piezoelectric constant
d33. As can be understood from this graph, from the viewpoint of the piezoelectric constant d33,
the subphase ratio is preferably in the range of 3 to 15 mol%, more preferably in the range of 3
to 10 mol%, and most preferably in the range of 4 to 6 mol% preferable.
[0072]
The electromechanical coupling coefficient kr (FIG. 4) of the samples S06 to S11 is equal to or
higher than that of the sample S04 of the comparative example, and all of them are preferable.
Sample S12 in which the subphase ratio is 20 mol% is not preferable in that the
electromechanical coupling coefficient kr is considerably smaller than that of the sample S04 of
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22
the comparative example. From the viewpoint of the electromechanical coupling coefficient, the
subphase ratio is preferably in the range of 3 to 10 mol%, and more preferably in the range of 4
to 6 mol%.
[0073]
Samples S05 and S08 have in common the point that the subphase ratio is 5 mol%. The major
difference between the two is that the first crystal phase of sample S05 contains Ca (calcium) as
element C while the first crystal phase of sample S05 does not contain element C (Ca, Sr, Ba) at
all. It is a point that In the samples S05 and S08, although the value of the coefficient x of the
composition formula of the second crystal phase is also different, the effect of the difference in
the value of the coefficient x on the characteristics of the piezoelectric ceramic composition as
discussed regarding the samples S01 and S02 Is estimated to be relatively small. Among the
samples S05 and S08, the sample S08 in which the first crystal phase contains Ca (calcium) has a
relative dielectric constant ε33 <T> / ε0, a piezoelectric constant d33, and an
electromechanical coupling coefficient kr. Both are excellent. Therefore, the first crystal phase
preferably contains Ca as the component element C. Similarly, similar effects can be expected
also when other alkaline earth elements (Sr, Ba, etc.) are contained as the component element C.
[0074]
Note that which of the three characteristics of relative permittivity ε33 <T> / ε0, piezoelectric
constant d33, and electromechanical coupling coefficient kr is important depends on the
application of the piezoelectric ceramic composition. For example, a composition having a large
relative dielectric constant ε33 <T> / ε0 is suitable for a capacitor. Further, a composition
having a large piezoelectric constant d33 is suitable for an actuator or a sensor. In addition, a
composition having a large electromechanical coupling coefficient kr is suitable for a
piezoelectric transformer or an actuator. The piezoelectric ceramic composition suitable for each
application is determined according to the characteristics required according to the application.
[0075]
Samples S13 and S14 of FIG. 4 are samples mainly for examining the influence of the element B
(Nb, Ta) of the second crystal phase. There is no large difference in any of the relative dielectric
constants ε33 <T> / ε0, the piezoelectric constant d33, and the electromechanical coupling
14-04-2019
23
coefficient kr. Therefore, as element B, it can be understood that both Nb and Ta are preferable.
[0076]
Further, the sample S14 has a composition close to that of the sample S08. That is, both differ
mainly in the amount of Ca as the component element C of the first crystal phase, and
accordingly the amounts of K and Na differ, and the other compositions are substantially the
same. Comparing the characteristics of the two, sample S14 with more Ca is preferable for
relative permittivity ε33 <T> / ε0, but sample S08 with less Ca for piezoelectric constant d33
and electromechanical coupling coefficient kr preferable.
[0077]
The sample S15 uses equal amounts of Ca and Sr (each at at%) as the component element C of
the first crystal phase, and in other respects, has a composition close to that of the sample S08.
The sample S15 is slightly inferior to the sample S08 in all in terms of relative permittivity ε33
<T> / ε0, piezoelectric constant d33, and electromechanical coupling coefficient kr. However,
the sample S15 is preferable in that the dielectric constant ε33 <T> / ε0 and the piezoelectric
constant d33 are sufficiently large as compared with the sample S04 of the comparative example.
Thus, a preferred composition can be obtained by using any of alkaline earth metals Ca and Sr as
the component element C of the first crystal phase. Therefore, it can be expected that similar
characteristics can be obtained even if Ba is used instead of Ca and Sr (or together with Ca and
Sr). However, if Ca is used as the component element C, it is possible to obtain a piezoelectric
ceramic composition that is inexpensive and has excellent characteristics.
[0078]
FIG. 6 shows the Curie point and the evaluation test result regarding the presence or absence of
the room temperature phase transition for the same samples S01 to S15 as FIG. 4. The samples
S05 to S15 have Curie points in the range of 300 to 350.degree. In general, the Curie point of the
piezoelectric ceramic composition is sufficient if it is 300 ° C. or higher, and therefore, all of the
samples S05 to S15 have a sufficiently high Curie point. Since the Curie point mainly depends on
the characteristics of the first crystal phase, it is estimated that the Curie point of the entire
piezoelectric ceramic composition does not fluctuate so much even if the composition of the
subphase or the proportion of the subphase changes to some extent. Be done. The samples S05
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24
to S12 and S14 to S15 using Nb as the component element B of the second crystal phase have a
higher Curie point than the sample S13 using Ta. Therefore, with respect to the Curie point, it is
preferable to use Nb rather than Ta as the component element B of the second crystal phase.
[0079]
As an evaluation test of the presence or absence of room temperature phase transition, the
relative dielectric constant ε 33 <T> / ε 0 was measured while gradually changing the
environmental temperature in the range of −50 ° C. to + 150 ° C. In general, a piezoelectric
ceramic composition having a phase transition in a certain temperature range exhibits an abrupt
change in which the relative permittivity ε33 <T> / ε0 has a clear peak in response to a
temperature change in the range. On the other hand, in the piezoelectric ceramic composition
having no phase transition in the temperature range, a clear peak does not appear in the change
of the relative permittivity ε33 <T> / ε0, and the change is gradual. Therefore, for the samples
S03 to S15 in FIG. 4, the phase transition is clearly observed from the change in relative
permittivity ε 33 <T> / ε 0 when the temperature is gradually changed in the range of −50 °
C. to + 150 ° C. It was judged whether or not it was done, and it was judged whether there was a
"room temperature phase transition" according to this. Here, the term "room temperature" can be
understood to mean a temperature range wider than normal room temperature (25.degree. C.).
[0080]
A room temperature phase transition was observed in samples S03 and S04 of the comparative
example. On the other hand, in each of the samples S05 to S15, no room temperature phase
transition was observed. The presence of a room temperature phase transition is not preferable
because the electrical properties and piezoelectric properties of the piezoelectric ceramic
composition largely change before and after that. From this point of view, the samples S05 to
S15 containing both the first crystal phase and the second crystal phase are preferable to the
samples S03 and S04 of the comparative example in that there is no room temperature phase
transition.
[0081]
FIG. 7 is a diagram showing experimental results on the influence of the coefficient e of the
composition formula of the matrix on the characteristics of the piezoelectric ceramic
14-04-2019
25
composition. At the top of FIG. 7, the characteristics of the sample S04 as a comparative example
are shown again. Among samples S21 to S27, among the coefficients a to f of the composition
formula of the first crystal phase, the values of the coefficients a to d are the same but the
coefficients e (the number of alkali-based elements at the A site) are different from each other.
The alkaline earth metal (element C of the composition formula) contained in the first crystal
phase is Ca (calcium). Further, the subphase ratio of each of the samples S21 to S27 is 5 mol%. In
the sample S21, the coefficient x of the composition formula of the second crystal phase is zero,
and all the other samples S22 to S27 have a coefficient x of 0.15. However, as described above,
the influence of the difference in coefficient x on the characteristics is small. The sample S25 is
the same as the sample S14 shown in FIG.
[0082]
The relative dielectric constants ε33 <T> / ε0 of the samples S21 to S27 are all preferable in
that they are sufficiently larger than the sample S04 of the comparative example. From the
viewpoint of relative dielectric constant, the value of the coefficient e of the composition formula
of the first crystal phase is preferably in the range of 0.97 to 1.1, and more preferably in the
range of 1.0 to 1.1. All of the samples S21 to S25 are preferable in that the piezoelectric constant
d33 is larger than the sample S04 of the comparative example. However, samples S26 and S27 in
which the coefficient e is larger than 1.08 are not preferable in that the piezoelectric constant
d33 is smaller than the sample S04 of the comparative example.
[0083]
FIG. 8 is a graph showing the values of the piezoelectric constant d33 for the samples S21 to
S27. The horizontal axis is the value of coefficient e of the composition formula of the first
crystal phase. The coefficient e indicates the ratio of the sum of the number of atoms of the alkali
metal element (K + Na + Li) and the alkaline earth metal element (element C of the composition
formula) to the number of atoms of Nb (niobium). As can be understood from this graph, from
the viewpoint of the piezoelectric constant, the value of the coefficient e of the composition
formula of the first crystal phase is preferably in the range of 0.97 to 1.08, and in the range of
1.00 to 1.07. Is more preferred.
[0084]
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26
In FIG. 7, the samples S26 and S27 are not preferable because the electromechanical coupling
coefficient kr is smaller than the sample S04 of the comparative example. From the viewpoint of
the electromechanical coupling coefficient, the value of the coefficient e of the composition
formula of the first crystal phase is preferably in the range of 0.97 to 1.08, and more preferably
in the range of 1.00 to 1.07.
[0085]
FIG. 9 is a diagram showing experimental results on the influence of the additive metal on the
characteristics of the piezoelectric ceramic composition. At the top of FIG. 9, the characteristics
of the sample S04 as a comparative example are shown again. Sample S31 is also a comparative
example composed of only the first crystal phase, and contains 1 mol% of Cu as an additive
metal. In this sample S31, although the relative permittivity ε33 <T> / ε0 is smaller than that
of the sample S04, the electromechanical coupling coefficient kr indicates a larger value than
that of the sample S04.
[0086]
Samples S32 to S43 are all compositions containing 5 mol% of the second crystal phase. Among
the coefficients a to f of the composition formula of the first crystal phase, the coefficients a and
b are slightly different for each sample, but the other coefficients c to f are substantially constant
values. The sample S32 is the same as the sample S08 described in FIG. 4 and contains no
additive metal.
[0087]
As can be understood from the samples S33 to S43, as additive metals, Cu (copper), Ni (nickel),
Co (cobalt), Fe (iron), Mn (manganese), Zr (zirconium), Ag (silver), Zn Even if it contains at least
one metal element of (zinc), Sc (scandium), and Bi (bismuth), a piezoelectric ceramic composition
having sufficiently good characteristics as compared with the samples S04 and S31 of the
comparative example is obtained. Can. In addition, also when Cr (chromium) is added, it can be
expected that the same characteristics as in the case where Mn (manganese) is added can be
obtained. As can be understood by comparing the three samples S32 to S34, the content ratio of
the additive metal is preferably less than 1 mol% for one type of additive metal. Moreover, it is
preferable that the sum total of the content rate of an addition metal shall be 5 mol% or less. It is
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27
not preferable to contain an additive metal in an amount larger than this because the relative
dielectric constant ε 33 <T> / ε 0 and the piezoelectric constant d 33 may decrease on the
contrary.
[0088]
FIG. 10 is a diagram showing experimental results on the influence of the presence or absence of
a secondary phase on the insulation of the piezoelectric ceramic composition. Here, measured
values of the applicable voltage are shown for the samples S03, S04, and S08 described in FIG. 4
and the sample S35 described in FIG. The “applicable voltage” means a maximum applied
voltage at which breakage such as cracking does not occur in the piezoelectric ceramic 100 when
a voltage is applied to the piezoelectric element 200 of each sample. In the measurement of FIG.
10, a voltage was applied for 30 minutes in an environment of 80 ° C., and it was checked
whether breakage such as cracking occurred in the piezoelectric ceramic 100. This applicable
voltage can be considered to indicate the insulation of the piezoelectric ceramic composition.
[0089]
The applicable voltages of the samples S03 and S04 having no subphase were both 3 kV / mm,
and the applicable voltages of the samples S08 and S35 containing 5 mol% of the subphase were
7 kV / mm and 9 kV / mm. From this experimental result, it can be understood that the
insulation property of the piezoelectric ceramic composition is also improved by making the
structurally stable subphase (second crystal phase) coexist with the first crystal phase.
[0090]
FIG. 11 is a diagram showing an analysis result of the second crystal phase in the piezoelectric
ceramic composition. The first four samples S06, S08, S10 and S12 are the same as the
piezoelectric ceramic compositions of these sample numbers shown in FIG. Further, samples S33,
S35, S36, S40 and S42 are the same as the piezoelectric ceramic compositions of these sample
numbers shown in FIG. The subphase (NTK phase) was analyzed by performing XRD analysis (Xray diffraction) and TEM-EDS analysis (energy dispersive X-ray analysis using a transmission
electron microscope) on these nine samples. In addition, although the composition of a subphase
can usually be confirmed by X-ray diffraction, when there are few addition amount and
generation amount, it is possible to confirm by methods, such as TEM-EDS.
14-04-2019
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[0091]
The two rightmost columns in FIG. 11 show the analysis results. In these columns, "1115" means
1115 phase (KTiNbO5 phase), and "1319" means 1319 phase (KTi3NbO9 phase). As understood
from this analysis result, the secondary phase of the piezoelectric ceramic composition is
composed of only the 1115 phase, that of the 1319 phase, and that of the 1115 phase and the
1319 phase. There may be cases where In particular, when an additive metal is added, it can be
understood that the 1319 phase is often formed as a subphase.
[0092]
All the samples described in FIGS. 3 to 9 including the nine samples in FIG. 11 are manufactured
using the subphase material prepared as the 1115 phase in the manufacturing process. That is,
after the auxiliary phase material which is 1115 phase is prepared in steps T130 and T140 of
FIG. 1 and this auxiliary phase material is mixed with the matrix material in step T150, it is
manufactured by baking of step T160. Therefore, it is estimated that the 1319 phase in the
subphase of each sample in FIG. 11 is one converted from the 1115 phase at the time of firing in
step T160. As described in FIGS. 4 and 9, the samples listed in FIG. 11 have any of the electrical
characteristics (dielectric constant .epsilon.33 <T> /. Epsilon.0) and the piezoelectric
characteristics (piezoelectric constant d33 and electromechanical coupling coefficient kr). Also
show excellent characteristics. Therefore, it is possible to obtain a piezoelectric ceramic
composition having excellent characteristics whether the secondary phase after firing is any of
1115 phase and 1319 phase.
[0093]
FIG. 12 is a diagram showing analysis results of a piezoelectric ceramic composition prepared by
mixing the subphase material prepared as the 1319 phase with the matrix phase material. The
sample S51 has a subphase ratio of 3 mol%, and the other samples S52 to S57 have a sub phase
ratio of 5 mol%. Further, in the samples S51 and S52, no additive metal is added, but in the other
samples S53 to S57, Cu, Fe, Zn, Mn and the like are respectively added as additive metals. In
these samples, the subphase material which is the 1319 phase is prepared in steps T130 and
T140 of FIG. 1, and this subphase material is mixed with the matrix material in step T150, and
then manufactured by firing in step T160. According to the analysis results of these samples S51
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29
to S57, it was found that all subphases are 1319 phases. Further, these samples S51 to S57, like
samples S35 and S36 in FIG. 11 (see FIG. 9), have electrical characteristics (dielectric constant
.epsilon.33 <T> /. Epsilon.0) and piezoelectric characteristics (piezoelectric constant d33 and
electric machine) Excellent characteristics were shown in any of the coupling coefficients kr) (not
shown).
[0094]
FIG. 13 is a diagram showing the results of experiments conducted on samples S61 to S81
different from the samples S32 to S43 shown in FIG. 9 regarding the influence of the additive
metal on the characteristics of the piezoelectric ceramic composition. At the top of FIG. 13, the
characteristics of the samples S04 and S31 as the comparative example shown in FIG. 9 are
shown again. Each sample was prepared using a second crystalline phase prepared as the 1115
phase. Samples S61 to S80 in FIG. 13 all contain 5 mol% of the second crystal phase, and sample
S81 does not contain the second crystal phase. Further, among the samples S61 to S81, the
samples other than the samples S69, S72, and S76 contain two of Ca, Sr, and Ba as the element C
of the first crystal phase. The column of elements C1 and C2 in the column of the first crystal
phase indicates these two elements. The columns of coefficients d1 and d2 are coefficients of
elements C1 and C2.
[0095]
Among the samples S61 to S81, in the last two samples S80 and S81, the composition was not
sufficiently densified in the firing of step T160 of FIG. The reason for this is estimated that, for
the sample S80, the coefficient e for the entire A site is 1.12, and the value of the coefficient e is
too large. However, the sample S79 having a coefficient e of 1.09 and the sample S78 having a
coefficient e of 0.98 have electrical characteristics (relative dielectric constant ε 33 <T> / ε 0)
and piezoelectric characteristics (piezoelectric constant d 33 and electromechanical system
Excellent characteristics are shown in any of the coupling coefficients kr). In consideration of the
results of FIG. 13 comprehensively, in the case where the additive metal is contained, the value of
the coefficient e of the composition formula of the first crystal phase is preferably in the range of
0.97 to 1.10. The range of 00 to 1.09 is more preferable.
[0096]
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As can be understood from FIGS. 11 and 9, as additive metals, Cu (copper), Ni (nickel), Co
(cobalt), Fe (iron), Mn (manganese), Zr (zirconium), Ag (silver) Even if it contains at least one
metal element of Zn, Zn (zinc), Sc (scandium), and Bi (bismuth), a piezoelectric ceramic
composition having sufficiently good characteristics as compared with the samples S04 and S31
of the comparative example You can get it. In addition, when Cr (chromium) is added, it can be
expected that the same characteristics as when Mn (manganese) is added can be obtained.
[0097]
FIG. 15 is a diagram showing the results of the thermal cycle evaluation test of the piezoelectric
ceramic composition. Here, tests were performed on the three samples S04, S31, and S32 shown
in FIG. 9 and the eight samples S61 to S65 and S67 to S69 shown in FIG. In the thermal cycle
evaluation test, first, the sample was put in a constant temperature bath, and the piezoelectric
characteristics at room temperature were evaluated (field of “initial value” of
electromechanical coupling coefficient kr in FIG. 14). Thereafter, the temperature cycle was
repeated at a temperature of 2 ° C./min at −50 ° C., 150 ° C., 20 ° C., 150 ° C., 20 ° C.
and so on. The holding time at each temperature at this time was 1 hour. Each time, the
piezoelectric properties were again evaluated at room temperature ("After thermal cycling"
column).
[0098]
As can be understood from the results of FIG. 14, in the samples S04 and S31 not including the
second crystal phase, the reduction ratio of the electromechanical coupling coefficient kr after
the thermal cycle is about 70%, which indicates a large reduction ratio. . On the other hand, in
the samples S32, S61 to S65, and S67 to S69 containing the second crystal phase, the reduction
rate of the electromechanical coupling coefficient kr after thermal cycling is in the range of about
10% to about 26%, which is sufficiently small. It was a good value. As described above, since the
piezoelectric ceramic composition containing the second crystal phase does not have an
excessive decrease in characteristics even when subjected to thermal cycling, applications
requiring excellent thermal durability (for example, knock sensor and combustion) Pressure
sensor etc.).
[0099]
Reference Signs List 1 knock sensor 2 main body metal fitting 2a through hole 2b cylindrical
body 2c bearing surface portion 2d screw thread 2e groove 3 insulating sleeve 4 insulating plate
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5 insulating plate 6 piezoelectric element 6a electrode 6b electrode 6c: Piezoelectric porcelain 7:
Weight for characteristic adjustment 8: Washer 9: Nut 10: Housing 20: Langevin type ultrasonic
transducer 22: Piezoelectric element pair 23a, 23b: Piezoelectric element 24a, 24b: Electrode
plate 25: front plate 26: front plate 26 Backing plate 27 Center bolt 28, 29 Conical portion 30
Ultrasonic radiation surface 31 Blind end hole 40 Ultrasonic cutting tool 42 Spindle 43
Piezoelectric element 44 Mounting jig 45 Grinding portion 46 Base material 47 Arrow indicating
direction of vibration 48: Arrow indicating direction of rotation of spindle 100: Piezoelectric
porcelain 200: Piezoelectric element 301, 302: Electrode
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