JP5860350B2 - Polymer composite piezoelectric body and piezoelectric element using the same - Google Patents

Description

  The present invention relates to a polymer composite piezoelectric body suitable for a sensor, an ultrasonic probe, a vibration power generator, and the like, and a piezoelectric element using the piezoelectric body.

  A polymer piezoelectric material is a piezoelectric material with characteristics peculiar to polymer materials such as flexibility, impact resistance, ease of processing, and large area, and power output constant compared to inorganic piezoelectric materials. (Piezoelectric g constant) is high and the acoustic impedance is close to that of the human body and water, so it is applicable to various sensors, ultrasonic transducers, ultrasonic transducers such as hydrophones, damping materials (dampers), and vibration power generation. Is expected. In these application fields, both the piezoelectric strain constant (d constant), which is an index of strain amount (transmitting ability) per unit electric field, and the g constant, which is an index of generated electric field strength (receiving ability) per unit stress. There is a need for piezoelectric materials that are excellent in size or balance.

  As a polymer piezoelectric material, a piezoelectric polymer having a piezoelectric property in a polymer substance itself represented by polyvinylidene fluoride (PVDF) is known, but the d constant is lower than that of an inorganic piezoelectric material. When used in applications, sufficient performance cannot be obtained.

  On the other hand, a piezoelectric material-polymer piezoelectric composite (polymer composite piezoelectric material, hereinafter referred to as a piezoelectric composite) that provides a piezoelectric property by using a polymer material as a matrix and composites an inorganic piezoelectric material in the matrix is the above polymer. This is a piezoelectric material that takes advantage of the material's unique advantages and excellent piezoelectric performance (d constant) of inorganic piezoelectric material. The type of polymer used as matrix, the type and composition of inorganic piezoelectric material, connectivity, shape, and compounding ratio It has been attracting attention as a piezoelectric material that can be designed in accordance with various applications by changing.

In general, the piezoelectric characteristics of a piezoelectric composite tend to be lower than the piezoelectric characteristics of the piezoelectric body itself. Accordingly, lead-based piezoelectric materials such as lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT) having high piezoelectric performance are mainly used as the piezoelectric body used in the piezoelectric composite.

  On the other hand, since lead is a highly toxic element, environmental problems such as soil contamination and air pollution due to waste from the waste and materials used in the manufacturing process, and disposal after use are inevitable. There is an increasing demand for lead-free piezoelectric composites. However, since the current lead-free piezoelectric material has a d constant that is inferior to that of lead, it is difficult to obtain high piezoelectric performance comparable to that of lead-based piezoelectric composites.

Patent Document 1 discloses a piezoelectric composite comprising a bismuth layered compound and a piezoelectric polymer (a copolymer of PVDF and ethylene trifluoride). Non-Patent Document 1 describes a piezoelectric composite composed of (Bi, Na) TiO ₃ —BaTiO ₃ (BNT-BT) and a piezoelectric polymer (a copolymer of PVDF and ethylene trifluoride).

  Non-Patent Document 2 describes a power generation element using a piezoelectric composite formed by dispersing conical non-doped zinc oxide nanowires in PMMA as a power generation element capable of driving a commercially available small liquid crystal display. In this document, by making the zinc oxide particles have a cone shape with a cone angle of 0.87 °, the behavior of the monopolar generator is similar to that of a monopolar generator. I am trying.

Japanese Patent No. 3075447

Kwok-ho Lam et. Al, “Piezoelectric and pyroelectric properties of (Bi0.5Na0.5) 0.94Ba0.06TiO3 / P (VDF-TrFE) 0-3 composites.”, Composites part A 36 (2005) 1595-1599. Youfan Hu et al., “High-Output Nanogenerator by Rational Unipolar Assembly of Conical Nanowires and Its Application for Driving a Small Liquid Crystal Display.”, Nano Lett. 2010, 10, 5025-5031.

  The piezoelectric composites of Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2 are both lead-free materials, which are preferable in terms of environmental friendliness.

  However, the piezoelectric composite of Patent Document 1 uses a bismuth layered compound as an inorganic piezoelectric body. Since the bismuth layered compound has a Curie point of 500 ° C. to 800 ° C., which is higher than PZT, it has an advantage of excellent thermal stability. However, the piezoelectric performance is as low as 20 pC / N regardless of the content of the piezoelectric material.

  Similarly, in the material system of Non-Patent Document 1, a relatively high pyroelectric performance is obtained, but a high piezoelectric performance is not obtained. The piezoelectric composite of Non-Patent Document 2 is intended to improve piezoelectricity by shape control, requires precise shape control, and has low piezoelectric performance.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a lead-free polymer composite piezoelectric body having good piezoelectric performance.

The polymer composite piezoelectric material of the present invention includes an organic polymer resin and a plurality of piezoelectric materials dispersed in the organic polymer resin,
The piezoelectric body is made of a wurtzite complex oxide having a composition represented by the following general formula (P) (may contain inevitable impurities): Zn _x (A _y , B _z , C _w ) O (P)
(In formula (P), 0.6 ≦ x <1, y + z + w ≠ 0, A: at least one selected from the group consisting of Li, Na, and K, which is a monovalent M-site element having an ionic valence. B: an M site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. : M site element having an average ion valence larger than 2 and Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and W And at least one metal element selected from the group consisting of:

  In the present specification, the polymer composite piezoelectric material means a composite of an organic polymer resin and a piezoelectric material, and generally refers to what is called “piezoelectric composite, composite piezoelectric material” (Japan Ceramics Corporation). Association edition, “Ceramic composite, Chapter 2 Ceramic-plastic piezoelectric composite”, Baifukan).

  It is known that the wurtzite type complex oxide whose base oxide is zinc oxide is relatively easy to generate oxygen vacancies, and the composition of the general formula (P) is within the range that can take a wurtzite type crystal structure. It may deviate from the stoichiometric composition. The wurtzite crystal structure is a hexagonal crystal structure represented by the general formula MX represented by ZnS and ZnO, in which four elements X are coordinated around the element M, and M is around the X. Four are coordinated.

  In this specification, “being a piezoelectric body” means a level of insulation that does not cause a problem of leakage current when a piezoelectric element is used, that is, an electrical resistivity is an insulator region (200 MΩ / □ or more), and a substance This means that when a pressure is applied, the material has a property of causing a polarization proportional to the pressure to cause surface charge to appear, and conversely, when an electric field is applied, the material is deformed.

  In the polymer composite piezoelectric material of the present invention, the difference between the dielectric constant of the wurtzite complex oxide and the dielectric constant of the organic polymer resin is preferably within 50% of the dielectric constant of the piezoelectric material, More preferably, it is within 10%. The organic polymer resin preferably has a dielectric constant of 7 or more.

  Each of the plurality of piezoelectric bodies has crystal orientation, and it is preferable that the plurality of piezoelectric bodies are arranged so that the polarization directions thereof are substantially parallel and dispersed in the organic polymer resin. The plurality of piezoelectric bodies preferably have c-axis orientation.

In this specification, “having crystal orientation” is defined as an orientation rate F measured by the Lottgering method being 80% or more. The orientation rate F is preferably 90% or more, and more preferably 95% or more.
The orientation rate F is represented by the following formula (i).
F (%) = (P−P0) / (1−P0) × 100 (i)
In formula (i), P is the ratio of the total reflection intensity from the orientation plane to the total reflection intensity. In the case of (00l) orientation, P is the sum ΣI (00l) of the reflection intensity I (00l) from the (00l) plane and the sum ΣI (hkl) of the reflection intensity I (hkl) from each crystal plane (hkl). ({ΣI (00l) / ΣI (hkl)}). For example, in the case of a (001) orientation in a wurtzite crystal, P = I (002) / [I (002) + I (100) + I (101) + I (102) + I (110) + I (103)].
P0 is P of a sample having a completely random orientation.
When the orientation is completely random (P = P0), F = 0%, and when the orientation is complete (P = 1), F = 100%.

The piezoelectric body has a dielectric constant of 15 or more and 40 or less, it is preferable piezoelectric constant _{d 33} is 50pc / N or more.

  The volume fraction of the piezoelectric body in the organic polymer resin is preferably 30% or more and 90% or less.

According to the present invention, a polymer composite piezoelectric body having a piezoelectric constant d33 of ₃₀ pC / N or more can be provided.

  The polymer composite piezoelectric material of the present invention preferably has 0-3 type connectivity or 1-3 type connectivity. Here, the connectivity of the polymer composite piezoelectric material means the connectivity of the composite proposed by Newham et al. (RE Newnham et. Al, Mater. Res. Bull. 13, 525 ( 1978)). Specifically, the polymer composite piezoelectric body is regarded as a dice-like assembly, and when the XYZ three axes are decomposed, the number of axes that the piezoelectric body self-connects among the three axes is m, and the polymer is three axes. Of these, the number of self-connected axes is n, which is shown as mn connectivity.

  The 1-3 type connectivity means a structure in which the piezoelectric body is self-connected only in one axial direction and the polymer is self-connected in all three axes. 0-3 connectivity is a structure in which the piezoelectric body is not self-connected to any axis, and the polymer is self-connected to all three axes, that is, the particulate piezoelectric body is in the organic polymer resin. It means that it is a dispersed mode.

The piezoelectric body is preferably made of a wurtzite complex oxide (which may include inevitable impurities) having a composition represented by the following general formula (PX) or (PY).
Zn _x (A _y , B _z , C _w ) O (PX)
(In formula (PX), 0.6 ≦ x <1, 0 ≦ y, 0 ≦ z, 0 <w,
A: M site element having a monovalent ionic valence, and at least one metal element selected from the group consisting of Li, Na, and K. B: M-site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. C: M site element having an average ion valence greater than divalent, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and And at least one metal element selected from the group consisting of W. )

Zn _x (A _y , B _z , C _w ) O (PY)
(In the formula (PX), 0.6 ≦ x <1, 0 <y, 0 ≦ z, 0 <w,
A: M site element having a monovalent ionic valence, and at least one metal element selected from the group consisting of Li, Na, and K. B: M-site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. C: M site element having an average ion valence greater than divalent, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and And at least one metal element selected from the group consisting of W. )

  In the polymer composite piezoelectric material of the present invention, when the element A is contained, the element A is preferably Li or Na. The polymer composite piezoelectric material of the present invention is preferably a piezoelectric film.

  A piezoelectric element according to the present invention includes the above-described polymer composite piezoelectric body according to the present invention and a pair of electrodes that sandwich the piezoelectric body.

  The polymer composite piezoelectric material of the present invention uses a piezoelectric material (which may contain inevitable impurities) made of a zinc oxide-based wurtzite composite oxide. The inventors of the present invention show that the oxide constant of a zinc oxide-based wurzite-type composite oxide, which has not been attracting much attention as a piezoelectric material, is lower than that of a lead-based perovskite-type oxide because of the low piezoelectric constant of the oxide itself. Therefore, it is possible to suppress a decrease in the piezoelectric constant that occurs when a polymer composite piezoelectric material is formed. In a polymer composite piezoelectric material using a zinc oxide-based wurtzite-type composite oxide as a piezoelectric material, a lead-based perovskite-type oxide is used. It has been found that it exhibits superior piezoelectric performance. ADVANTAGE OF THE INVENTION According to this invention, the lead-free polymer composite piezoelectric material with favorable piezoelectric performance can be provided.

  A Zn site (M site) of zinc oxide, which is a base oxide, includes a metal element having an ionic valence of 1 and a metal element having a valence of more than 2 having a piezoelectric property and a wurtzite structure. In a mode in which a zinc oxide-based wurtzite complex oxide (which may contain inevitable impurities) containing a total amount of 40 mol% or less within a range that can take up the above is used as a piezoelectric body, good insulation and piezoelectric characteristics It is possible to provide a lead-free polymer composite piezoelectric material having:

1 is a schematic diagram showing the structure of a polymer composite piezoelectric body (piezoelectric composite) having 1-3 connectivity according to an embodiment of the present invention. The schematic diagram which shows the structure of the piezoelectric composite which has 0-3 connectivity of embodiment which concerns on this invention Diagram showing Banno's improved cube model Diagram showing the unit cell of Banno's improved cube model It shows the effect on the piezoelectric constant d ₃₃ of the piezoelectric composite of the dielectric constant of the piezoelectric It shows the effect on the piezoelectric constant g ₃₃ of the piezoelectric composite of the dielectric constant of the piezoelectric Diagram showing influence of dielectric constant of piezoelectric material on power generation index of piezoelectric composite Diagram showing the relationship between the volume fraction and the piezoelectric constant d ₃₃ in the piezoelectric composite of V-doped zinc oxide The figure which shows the relationship between the volume fraction and power generation index in the piezoelectric composite of V dope zinc oxide For V-doped zinc oxide and PZT, and compared the relationship between the volume fraction and the piezoelectric constant d ₃₃ in the piezoelectric composite drawing For V-doped zinc oxide and PZT, and compared the relationship between the volume fraction and the piezoelectric constant g ₃₃ in the piezoelectric composite drawing Comparison of the relationship between volume fraction and power generation index in piezoelectric composites for V-doped zinc oxide and PZT Schematic showing one crystal lattice of non-doped zinc oxide Schematic showing one crystal lattice of co-doped zinc oxide Diagram showing the relationship between dopant valence and ion radius Sectional drawing which shows the principal part which shows the structure of the piezoelectric element of embodiment which concerns on this invention

"Polymer composite piezoelectric material (piezoelectric composite)"
A polymer composite piezoelectric body (piezoelectric composite) according to an embodiment of the present invention will be described with reference to the drawings. Piezoelectric composites have several types of connectivity between the piezoelectric body and the organic polymer resin, and a suitable connectivity may be selected according to the required performance. The difference in performance due to connectivity is described in the literature relating to piezoelectric composites including the above-mentioned literature edited by the Japan Ceramic Society.

  1A schematically illustrates a piezoelectric composite having 1-3 connectivity (hereinafter referred to as 1-3 composite), and FIG. 1B schematically illustrates a piezoelectric composite having 0-3 connectivity (hereinafter referred to as 0-3 composite). FIG.

  In the 1-3 composite of FIG. 1A, the piezoelectric composite 1a includes a columnar (fiber-like) piezoelectric body 11a in an organic polymer resin 12a, and the major axis direction of the piezoelectric body 11a is substantially parallel to the z-axis shown in the figure. In this way, a plurality of pieces are independently arranged. One columnar piezoelectric body 11 a has connectivity only in the z-axis direction, and the periphery of the column is covered with an organic polymer resin 12.

  The piezoelectric composite 1a may be manufactured by a method of manufacturing a normal 1-3 composite. For example, an array-shaped columnar piezoelectric body 11a is manufactured using a die casting method or a multi-blade wafer ring saw for wafer manufacturing, It can be produced by a method of pouring an organic polymer resin into the gap between the arrays.

  In general, when the electric field is applied to the 1-3 piezoelectric composite 1a, the columnar piezoelectric body 11a can easily stretch because the surrounding organic polymer resin is soft. In the piezoelectric composite 1a, the dielectric constant approaches the piezoelectric body 11a as the volume fraction of the piezoelectric body 11a increases. Since the piezoelectric g constant is inversely proportional to the dielectric constant, the piezoelectric g constant becomes smaller as the volume fraction of the piezoelectric body 11a having a higher dielectric constant than that of the polymer material increases.

  In addition, as shown in FIG. 1B, the 0-3 composite 1b is a piezoelectric material having no connectivity in any of the xyz directions in the organic polymer resin 12b, such as particles, needles, whiskers, etc. 11b is present in a dispersed state.

  The 0-3 composite may be prepared using a normal 0-3 composite preparation method or a polymer film preparation method. For example, a piezoelectric polymer powder is mixed and kneaded in a molten polymer matrix material, and a manufacturing method using a melt film forming technique such as injection molding, extrusion molding or a T-die method, or a solution film forming such as casting is used. Can be produced.

  Since the 0-3 composite has no connectivity of the piezoelectric body 11b as compared with the 1-3 composite, the piezoelectric d constant is also easily affected by the volume fraction. Moreover, it can have a g constant superior to that of the piezoelectric body 11b.

  Regardless of the 1-3 composite or the 0-3 composite, each of the plurality of piezoelectric bodies 11a and 11b has crystal orientation, and the polarization directions of the plurality of piezoelectric bodies are substantially parallel. The aspect which arrange | positions so that it may become and is disperse | distributed in organic polymer resin is preferable. The plurality of piezoelectric bodies 11a and 11b preferably have c-axis orientation.

  The piezoelectric composites 1a and 1b are preferably subjected to polarization treatment. Regardless of the aspect of the 1-3 composite or the 0-3 composite, it is preferable to perform polarization treatment after the composite. The method of polarization treatment is not particularly limited, and examples thereof include a normal polarization method in which an electric field is applied to the piezoelectric composites 1a and 1b in the film thickness direction, and corona polarization.

  The present inventors have designed the material of a piezoelectric composite including a plurality of piezoelectric bodies dispersed in an organic polymer resin, and use a piezoelectric body made of a zinc oxide-based wurtzite complex oxide as the piezoelectric body. As a result, the inventors have found that the piezoelectric characteristics are not significantly lowered by compositing, and can have excellent electrical characteristics that cannot be achieved by a piezoelectric composite using a perovskite oxide as a piezoelectric body.

  For the theoretical calculation of the electrical properties of piezoelectric composites, Banno has proposed an “improved cube model” that takes into account the anisotropic distribution in the x, y and z directions (Jpn. J. Appl. Phys. 24 Suppl). 24-2 (1985) 445), which is known to have good agreement with experimental values.

  The present inventor has designed the material of the piezoelectric composite using the Banno model. FIG. 2A is an improved cubic model of Banno of 0-3 composite, FIG. 2B is a unit cell model thereof, and in FIG. 2A, phase 1 is a piezoelectric phase and phase 2 is an organic polymer resin phase.

  The present inventor has shown characteristics of a piezoelectric material and a composite in the case of a uniaxial anisotropic material (l = m = 1, n ≠ 1) in a Banno model 0-3 composite. Calculated.

In FIG. 2B, in the case of a uniaxial anisotropic material, the dielectric constant ^* ε ₃₃ , the piezoelectric constant ^* d _{33 of} the 0-3 composite, and the volume fraction ¹ V of the piezoelectric phase (phase 1) are expressed by the following equations. be able to.

Incidentally, the subscript notation d ₃₃ and epsilon _33, when defining the three axes 1, 2 and 3 orthogonal, the first subscript is the electric field application direction, the second subscript indicates the direction of the strain, the strain Alternatively, the direction in which the stress is taken out is a longitudinal vibration mode that is parallel to the direction in which the electric field is applied. Accordingly, d ₃₃ and ε ₃₃ indicate the piezoelectric strain constant and dielectric constant of the longitudinal vibration mode.

The piezoelectric g constant g ₃₃ that is an index of the generated electric field strength (reception ability) per unit stress is expressed by the following equation using d ₃₃ and ε ₃₃ .
g ₃₃ = d ₃₃ / ε ₃₃

3A to 3C show a case where a resin having a dielectric constant ¹ ε ₃₃ of 18, ¹ d ₃₃ = 0 is used as an organic polymer resin, and a piezoelectric body having a dielectric constant ² ε ₃₃ of 5, 10, 20, 50 is used as a piezoelectric body. When used, the values of piezoelectric constants d ₃₃ and g ₃₃ and power generation index (performance) d ₃₃ × g ₃₃ in the case of composite formation with respect to the piezoelectric constant of the piezoelectric body are plotted. In the calculation, the n value of the unit cell shown in FIG. 2B was 0.14, and the a value was a value at which the volume fraction of the piezoelectric body was 0.6. About FIG. 3B and FIG. 3C, the plot of PVDF (polyvinylidene fluoride) which is a piezoelectric polymer is also shown as reference.

  As shown in FIG. 3A to FIG. 3C, as the dielectric constant of the piezoelectric body increases, the rate of decrease in the piezoelectric constant and power generation performance when composited is increased. In particular, the change is significant for the g constant and the power generation performance d33 × g33 that are greatly influenced by the dielectric constant.

  From the results of FIGS. 3A to 3C, it was confirmed that a decrease in the piezoelectric constant at the time of compositing can be suppressed by using a material having a low dielectric constant while maintaining the piezoelectric d constant as the piezoelectric material to be composited.

  Moreover, although the dielectric constant of a piezoelectric material is a value peculiar to a material, in the case of a piezoelectric material, it is known that the dielectric constant in the polarization axis direction is small. Therefore, by aligning and polarizing the piezoelectric body and making the polarization axis direction and the displacement direction (in this case the thickness direction) substantially coincide, the dielectric constant is lowered and the decrease in piezoelectric constant when composited is suppressed. I think it can be done.

  Therefore, the present inventors have repeatedly studied on a lead-free piezoelectric material having a low dielectric constant, and designed a material by paying attention to a zinc oxide-based wurtzite oxide whose base oxide is zinc oxide. went.

  A polymer composite material (composite material) containing a zinc oxide-based wurtzite oxide whose base oxide is zinc oxide is, for example, an electrode material for a light transmissive device, as described in JP 2011-44679 A Are already known in the application.

  However, as already mentioned, in the case of compositing a piezoelectric material, the piezoelectric property is generally lower than the piezoelectric property of the piezoelectric material itself. Therefore, the piezoelectric property of the piezoelectric material itself is lower than that of a perovskite oxide such as PZT. Thus, the extremely low zinc oxide-based piezoelectric material has hardly been studied as a composite material, and has recently been studied by shape control using ZnO nanofibers as described in Non-Patent Document 2. As mentioned above, the piezoelectric performance is still low. Conventionally, zinc oxide has low piezoelectric properties and has been considered difficult as a substitute for lead-based piezoelectric materials. However, in recent years, as shown in Non-Patent Documents I and II, the improvement of piezoelectric properties can be achieved by doping with donor ions. Possibilities have been found.

Non-patent literature “I: YC Yang et al.,“ Giant piezoelectric d33 coefficient in ferroelectric vanadium doped ZnO films ”, Applied Physics Letters 92, 012907, 2008.”, “II: Pan Feng et al.,“ Giant piezoresponse and promising . application of environmental friendly small-ion -doped ZnO ", Science China Vol 55, No.2: 421-436, in 2012.", etc., by the V-doped, a dozen times the d ₃₃ value of the non-doped ZnO d ₃₃ = 170 pC / N (V concentration 2.5 at.%), D ₃₃ = 110 pC / N (V concentration 2.5 at.%) Was reported to be achieved with an average value of 20 points.

In the same manner as described above, the present inventor uses V-doped zinc oxide as the piezoelectric body ( ² ε ₃₃ is 20, ² d ₃₃ = 170 pC / N), and the dielectric constant ¹ ε ₃₃ is 18, ¹ d as the organic polymer resin. _When the resin of ₃₃ = 0 is used, the dielectric constant of the piezoelectric composite ^* ε ₃₃ and the piezoelectric constants ^* d ₃₃ , ^* g ₃₃ , and the power generation index (performance) ^* d ₃₃ × ^* g ₃₃ are improved by Banno. Calculations were made using a cubic model (0-3 composite).

When the n value of the unit cell shown in FIG. 2B is 0.14 and the value a is a value at which the volume fraction of the piezoelectric body is 0.6, the dielectric constant ^* ε ₃₃ of the piezoelectric composite is 19, ^* d ₃₃ = 158 pC / N, ^* g ₃₃ = 939 mVm / N, and power generation index (performance) ^* d ₃₃ × ^* g ₃₃ = 148396.

When the same calculation is performed on PZT particles having ² ε ₃₃ of 1230 and ² d ₃₃ = 320 pC / N, the dielectric constant of the piezoelectric composite ^* ε ₃₃ is 193, ^* d ₃₃ = 87 pC / N, ^* g ₃₃ = 51 mVm / N, and the power exponent _{^{(performance) * d 33 × * g 33}} = 4429.

  These calculation results show that even if the oxide constant of the oxide itself is only about half that of PZT, the piezoelectric composite may outperform its piezoelectric performance even if it is a zinc oxide-based wurtzite complex oxide. .

The present inventors further designed the material of the piezoelectric composite using V-doped zinc oxide by changing the piezoelectric concentration in the resin and the n value (density in the thickness direction) of the 0-3 composite. . Here 20-point average value described in Non-Patent Document I ⁽² epsilon ₃₃ is _{^{20, 2 d 33 = 110pC /}} N) was calculated using the. The results are shown in FIGS. 4A and 4B.

FIG. 4A shows the change of the piezoelectric constant ^* d ₃₃ when the volume fraction of the piezoelectric body in the piezoelectric composite is changed. In the unit cell shown in FIG. 2B, the two types of plots are when the n value (density in the thickness direction) is 1 when l = m = 1 and when 0.1, When = 1, the unit cell is cubic, that is, isotropic. When n = 0.1, the piezoelectric particles are arranged at high density in the thickness direction.

Figure 4B, except that the vertical axis ^* d ₃₃ × ^* g ₃₃ value is the same as Figure 4A.

  4A and 4B show that in the piezoelectric composite using V-doped zinc oxide, the piezoelectric particles are arranged more densely in the thickness direction even if the volume fraction of the piezoelectric particles is reduced. It has been shown that performance can be maintained.

The same calculation is performed on PZT particles having ² ε ₃₃ of 1230, ² d ₃₃ = 320 pC / N, and n = 0.1, together with the calculation results of V-doped zinc oxide, FIGS. 5A to 5C. Shown in FIGS. 5A to 5C show changes in ^* d ₃₃ , ^* g ₃₃ , ^* d ₃₃ × ^* g ₃₃ when the volume fraction of the piezoelectric body in the piezoelectric composite is changed.

As shown in FIG. 5A, in the V-doped zinc oxide, as compared with PZT, even when the volume fraction in the piezoelectric composite is decreased, the decrease in the piezoelectric constant ^* d ₃₃ is moderate, and in the region where the volume fraction is low. ^* d ₃₃ value is reversed, towards the V--doped zinc oxide is high. Further, the piezoelectric g constant and the power generation index ^* d ₃₃ × ^* g ₃₃ value shown in FIGS. 5B and 5C are shown to have significantly superior values compared to PZT regardless of the volume fraction. Has been.

  As already described, the zinc oxide-based wurtzite oxide has a low piezoelectric performance, and has been considered unsuitable as a composite material in which the piezoelectric properties are lower than the original piezoelectric performance of the material. As described above, the inventor of the present invention has developed a lead-based perovskite type zinc oxide-based wurtzite-type composite oxide, which has not attracted much attention as a piezoelectric material, because of the low piezoelectric constant of the oxide itself. It has been found that the piezoelectric performance exceeds that of oxide. This indicates that the zinc oxide-based wurtzite oxide has the potential to play a very important role in making flexible piezoelectric devices.

  In addition, with the rapid increase in consumption of material resources, there is a growing interest in resource risks such as the scarcity of rare metals and rare earths, and device development using materials with relatively large reserves in the ground It is desired. Zinc oxide is also advantageous in that it is a relatively rich material.

  On the other hand, non-doped zinc oxide is difficult to obtain a piezoelectric composite having good piezoelectric properties because its own piezoelectric properties are too low. FIG. 6A is a schematic diagram showing one crystal lattice of non-doped zinc oxide. In the drawings of this specification, the scale of each part is appropriately changed and shown for easy visual recognition.

  As shown in FIG. 6A, the wurtzite crystal structure is a hexagonal crystal structure represented by a general formula MX typified by ZnS or ZnO, and the element X is a substantially tetrahedron around the element M. In general, four are coordinated, and four M are also coordinated around X. The distance between Zn and the four oxygens is substantially equal, and has a crystal structure in which Zn planes and O planes are alternately stacked along the c-axis (polar axis). For this reason, when strain is applied perpendicularly to the (001) plane (in the c-axis direction), it has a property of causing electric polarization.

  When the Zn sites of the ZnO crystal lattice shown in FIG. 6A are replaced with donor or acceptor ions, the charge balance is lost and the polarization is increased, resulting in improved piezoelectric properties. Therefore, in the present invention, a piezoelectric body (which may include inevitable impurities) made of a zinc oxide-based wurtzite complex oxide in which zinc oxide is doped with a donor or an acceptor is used as the piezoelectric body of the piezoelectric composite. FIG. 6B is a schematic view of one embodiment showing one crystal lattice of a zinc oxide-based wurtzite complex oxide, and shows an example in which a donor and an acceptor are co-doped.

  FIG. 6B shows that a donor whose ion radius is smaller than that of Zn ion enters the off-center position displaced from the center of gravity of the original Zn ion and induces a local dipole. Since the space is formed around the ions, it is easier to move, that is, more easily displaced. In terms of the effect of easy displacement due to the dopant ions entering the off-center position, even if the dopant ions are divalent ions having the same valence as Zn, the effect of improving the piezoelectric characteristics can be obtained.

That is, the piezoelectric composite 1 (a, b) of the present invention includes an organic polymer resin 12 (a, b) and a plurality of piezoelectric bodies 11 (a) dispersed in the organic polymer resin 12 (a, b). , B)
The piezoelectric body 11 (a, b) is characterized by being made of a wurtzite-type complex oxide having a composition represented by the following general formula (P) (may contain inevitable impurities).
Zn _x (A _y , B _z , C _w ) O (P)
(In formula (P), 0.6 ≦ x <1, y + z + w ≠ 0, A: at least one selected from the group consisting of Li, Na, and K, which is a monovalent M-site element having an ionic valence. B: an M site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. : M site element having an average ion valence larger than 2 and Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and W At least one metal element selected from the group consisting of:

  The volume fraction of the piezoelectric body 11 (a, b) in the piezoelectric composite 1 (a, b) is 30% to 90%, although it depends on the piezoelectric characteristics of the piezoelectric body and the piezoelectric characteristics required for the piezoelectric composite. Preferably there is.

  The organic polymer resin 12 (a, b) is not particularly limited as long as it is an organic polymer resin (including an elastomer). For example, general-purpose plastic such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene (PTFE), ABS resin (acrylonitrile butadiene styrene resin), acrylic resin, polyamide, polycarbonate, polyethylene terephthalate (PET), thermoplastic polyimide, etc. Engineering plastics, acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, butadiene rubber, silicone rubber and other synthetic rubber, polyvinylidene fluoride (PVDF) and its copolymers, piezoelectric polymers, phenolic resin, epoxy Resin, melamine resin, thermosetting resin such as polyimide, cyanoethylated polyvinyl alcohol, cyanoethylated pullulan, cyanoethylated vinyl alcohol And high dielectric constant cyanoresins such as cyanoethylated pullulan copolymer. What is necessary is just to select the organic polymer resin 12 which has a preferable physical characteristic according to the use and manufacturing method of a piezoelectric composite, and it is preferable that it is a thing with favorable bondability with the piezoelectric material 11 (a, b). .

  In the piezoelectric composite 1 (a, b), the difference between the dielectric constant of the piezoelectric body 11 (a, b) made of a wurtzite complex oxide and the dielectric constant of the organic polymer resin 12 (a, b) is as small as possible. This is preferable because it is possible to further suppress a decrease in piezoelectric constant accompanying a decrease in volume fraction of the piezoelectric body. The difference between the dielectric constant of the piezoelectric body 11 (a, b) made of the wurtzite complex oxide and the dielectric constant of the organic polymer resin 12 (a, b) is the dielectric constant of the piezoelectric body 11 (a, b). Is preferably within 50%, more preferably within 10%.

  In order to realize such a difference in dielectric constant, the dielectric constant of the organic polymer resin 12 (a, b) is preferably 7 or more. In the organic polymer resin exemplified above, a high dielectric constant cyanoresin such as cyanoethylated polyvinyl alcohol, cyanoethylated pullulan, cyanoethylated vinyl alcohol-cyanoethylated pullulan copolymer having a high dielectric constant is preferable.

  The piezoelectric composites 1a and 1b may each contain an additive or the like. For example, in the use of a damping material (damper), the electrical conductivity of the piezoelectric composite is adjusted by including conductive fine particles such as carbon black, carbon nanotubes, and metal particles. Thereby, it is set as the structure which made the state which forms a series circuit between a piezoelectric material and electroconductive fine particles, and vibration energy can be efficiently converted into thermal energy. Regardless of the conductive substance, an additive substance having desired characteristics may be used depending on the application.

  Hereinafter, a piezoelectric body 11 (a, b) (hereinafter referred to as a piezoelectric body 11) used for the piezoelectric composite 1 (a, b) of the present embodiment will be described including a new material design method.

  The piezoelectric body 11 is composed of zinc oxide doped with a dopant such as a donor or an acceptor, that is, a zinc oxide-based wurtzite complex oxide having a composition represented by the general formula (P) (may contain inevitable impurities). ).

  It is known that a wurtzite complex oxide whose base oxide is zinc oxide is relatively easy to cause oxygen deficiency. Therefore, the composition of the general formula (P) may deviate from the stoichiometric composition as long as the wurtzite crystal structure can be obtained.

  Zinc oxide can give various electrical characteristics from an insulator to a conductor by changing the kind and amount of dopant to be added. In other words, even if the constituent elements are the same, their electrical characteristics can change depending on the composition.

  In the above general formula (P), the composition that is a piezoelectric body varies depending on the types of elements A, B, and C. However, if each element is determined, the range of the composition that is a piezoelectric body is determined. Then, the x, y, z, and w values may be determined.

The piezoelectric body 11 preferably has a dielectric constant of 15 to 40 and a piezoelectric constant d ₃₃ of 50 pC / N or more. By using such a piezoelectric body 11, the piezoelectric composite 1 having a piezoelectric constant d33 of ₃₀ pC / N or more can be obtained.

Table 1 shows ionic valences and ionic radii of candidate elements of A ions and C ions in the general formula (P). In the non-patent documents I and II, the substitution ions for which the d ₃₃ value is indicated are shown together with the substitution amount and the d ₃₃ value.

  About the A element whose ionic valence is monovalent, from the viewpoint of the ion radius which can be doped, one or more kinds can be selected from Li, Na, and K. Among these, Li or Na having an ion radius close to that of Zn ions is preferable, and Li is more preferable.

  About the B element whose ionic valence is bivalent, from a viewpoint of the ion radius which can be doped, 1 type or multiple types can be selected from Mg, Ca, and Ni.

  The C element having an ionic valence greater than 2 is Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, One or more types can be selected from Mo, Ta, and W.

  As a dopant to the Zn site (M site) of zinc oxide, a monovalent metal ion is an acceptor ion (element A in the general formula (P)) and divalent than Zn having an ionic valence. A large metal ion can be a donor ion (C element in the general formula (P)), and from the viewpoint of improving the piezoelectric characteristics, a dopant having a smaller ionic radius is insulative as the valence is further away from the valence. The higher the concentration within the range that can be maintained, the better the balance of charge balance becomes and the polarization becomes larger, and the Coulomb force when an electric field is applied becomes larger.

  Considering substitution of Zn sites, the smaller the ionic radius of the dopant, the smaller the ionic radius of Zn (about 0.60Å), the easier it is to dope. The ion radius is not particularly limited.

  In the present specification, the “ion radius” means a so-called Shannon ion radius (see R. D. Shannon, Acta Crystallogr A32, 751 (1976)). The “average ionic radius” is an amount represented by ΣCiRi, where C is the molar fraction of ions in the lattice site and R is the ionic radius.

  The smaller the ion radius of the dopant ion than that of Zn, the more the dopant ion enters the off-center position displaced from the original center of gravity of the Zn ion to induce a local dipole, and around the dopant ion. It is considered that since the space is formed, it becomes easier to move, that is, more easily displaced, so that the piezoelectric characteristics are improved (see FIG. 6B). In the case of B element single doping, it is preferable that the element has an ion radius as small as possible within the range that can take a wurtzite structure.

  As for the donor ion, an element having a higher valence is preferable in terms of improving the piezoelectric characteristics, but a donor ion having a higher valence such as hexavalence is more likely to be unable to take a wurtzite structure from the viewpoint of charge balance. Difficult to do.

Since a dopant having a large valence can be selected, the piezoelectric body 11 is made of a wurtzite complex oxide represented by the following general formula (PX) doped with at least donor ions (including inevitable impurities). May also be preferred.
Zn _x (A _y , B _z , C _w ) O (PX)
(In formula (PX), 0.6 ≦ x <1, 0 ≦ y, 0 ≦ z, 0 <w,
A: M site element having a monovalent ionic valence, and at least one metal element selected from the group consisting of Li, Na, and K. B: M-site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. C: M site element having an average ion valence greater than divalent, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and And at least one metal element selected from the group consisting of W. )

As described above, zinc oxide has been considered to be difficult as an alternative material for lead-based piezoelectric materials because of its low piezoelectric properties. However, in recent years, as in Non-Patent Documents I and II, doping of donor ions is performed. Thus, the possibility of improving the piezoelectric characteristics has been found. However, in the methods of Non-Patent Documents I and II, the piezoelectric characteristic has already reached its peak, and it is 170 pC / N even in V-doping where the highest d ₃₃ value is obtained. This value is lower than the d ₃₃ value of the lead-based, it can not be said satisfactory piezoelectric characteristics. Further, considering that there is no report of the d ₃₃ value of the conventional zinc oxide-based piezoelectric material exceeding 30 pC / N, it is necessary to examine the insulating property that leads to the leakage current characteristics of the piezoelectric element.

The present inventor has found that, in the V-doped zinc oxide described in Non-Patent Documents I and II, the highest d ₃₃ value is obtained with a doping amount of 2.5 at. The material was designed with attention.

In the view of the present inventors, donor ions having a large valence have a relatively small ion radius and are easily doped, but the n-type becomes strong in a relatively low concentration region, the insulation properties deteriorate, and the piezoelectric properties deteriorate. . The present inventor has conducted intensive studies on a configuration that can achieve both a level of insulation that does not cause a problem of leakage current in a piezoelectric element and a charge balance that can provide high polarization. A total of 40 mol% of a metal element having an ionic valence of 1 and a metal element having an ionic valence of more than 2 in a Zn site (M site) within a range having piezoelectricity and a wurtzite structure. A technique for co-doping at the following ratio was found. Here, a preferable leakage current density as the piezoelectric element is 1 × 10 ⁻⁵ A / cm ² or less when an electric field having an intensity of about 10 kV / cm is applied.

That is, the piezoelectric body 11 is preferably made of a wurtzite complex oxide represented by the following general formula (PY) (which may contain inevitable impurities).
Zn _x (A _y , B _z , C _w ) O (PY)
(In the formula (PY), 0.6 ≦ x <1, 0 <y, 0 ≦ z, 0 <w,
A: M site element having a monovalent ionic valence, and at least one metal element selected from the group consisting of Li, Na, and K. B: M-site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. C: M site element having an average ion valence greater than divalent, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and And at least one metal element selected from the group consisting of W. )

  In this material design, a dopant ion having a property opposite to that of the dopant ion (dopant ion is a donor ion) while doping the dopant ion to increase the piezoelectricity by breaking the charge balance and securing the displacement space of the Zn site. If there is an acceptor ion, and if it is an acceptor ion, a donor ion is doped to ensure a level of insulation that does not cause a problem of leakage current when a piezoelectric element is formed.

  Furthermore, in the case of doping with donor ions alone, the resistivity decreases as the doping amount increases, and when a certain doping amount is exceeded, a donor element is deposited as a metal. For example, Non-Patent Document III relating to the study of ZnO vanadium-doped ZnO as a light emitter states that, with vanadium alone, the resistivity decreases as the doping amount increases, especially when the doping amount is greater than 3.5 at%. It is described that vanadium precipitates (Non-patent Document III: JT Luo et al., “Microstructure and photoluminescence study of vanadium-doped ZnO films.”, J. Phys. D: Appl. Phys. 42 115109, 2009 .).

  According to the above material design, the solid solution limit concentration can be increased, and thus a large piezoelectric improvement effect can be obtained by increasing the donor concentration.

  Either the A element ion or the C element ion may be used as a dopant for enhancing the piezoelectric characteristics. However, since the ion radius is small and an ion having a large difference in valence from the Zn ion can be selected, the C element ion can be selected. Is preferably used as a dopant for enhancing the piezoelectric characteristics, and a dopant for ensuring insulation by the element A ions.

  In the wurtzite complex oxide represented by the general formula (PY), since the charge balance is adjusted by co-doping with donor ions and acceptor ions, the insulation is maintained compared to the addition of only the dopant that enhances the piezoelectric characteristics. However, since the dopant addition concentration can be increased, the piezoelectric characteristics can be further improved.

FIG. 7 shows plots of some elements A and C with the valence as the horizontal axis and the ionic radius as the vertical axis. In FIG. 7, the ♦ plots are elements doped in Non-Patent Documents I and II, and these are shown together with the _d33 value described in the documents.

In FIG. 7, the d ₃₃ values for the dopants described in Non-Patent Documents I and II are slightly more or less, but the lower the right, that is, the higher the valence and the smaller the ionic radius, the more doped the dopant. A tendency to increase the effect of improving piezoelectricity is observed. Judging from this tendency, it is considered that Si, Ti, V, Nb, and Mo are suitable as the C element.

Once the C element is determined, the A element is selected, the composition of the wurtzite complex oxide is determined by adjusting the doping concentration of each element so that the desired d ₃₃ value is obtained within the piezoelectric range, A wurzeite-type composite oxide is produced under the conditions for the composition.

  The wurtzite complex oxide represented by the general formula (PY) may contain a divalent dopant element B other than Zn. Examples of the dopant element B include Mg, Ca, and Ni.

  The shape of the piezoelectric body 11 is preferably a shape suitable as the piezoelectric body 11 for piezoelectric composite. Therefore, as described above, columnar, needle-like, or whisker-like particles that can easily form 1-3 composites and 0-3 composites are preferable.

  Further, in order to obtain high piezoelectric performance as a piezoelectric body, it is preferable to have an aspect having crystal orientation, and it is more preferable to be an aspect in which it is polarized (alignment of polarization axes).

  The particle production method is not particularly limited, and a liquid phase method such as a coprecipitation method, a sol-gel method, or a hydrothermal synthesis method, or a gas phase method such as a PLD method or a CVD method can be used. Zinc oxide-based wurtzite-type composite oxide has excellent composition controllability, shape controllability, orientation controllability, and mass productivity in the production of particles, and is particularly excellent in shape controllability and orientation controllability. This is a feature not found in lead-based perovskite-type oxides, and is preferable because the structural design of the composite is easy.

  As described above, the piezoelectric composite (polymer composite piezoelectric body) 1 uses, as the piezoelectric body 11, a piezoelectric body made of a zinc oxide-based wurtzite complex oxide (which may contain inevitable impurities). The inventors of the present invention show that the oxide constant of a zinc oxide-based wurzite-type composite oxide, which has not been attracting much attention as a piezoelectric material, is lower than that of a lead-based perovskite-type oxide because of the low piezoelectric constant of the oxide itself. Therefore, it is possible to suppress a decrease in piezoelectric constant that occurs when a piezoelectric composite is formed. In the piezoelectric composite 1 using the zinc oxide-based wurtzite-type composite oxide as the piezoelectric body 11, the piezoelectric performance exceeds that of the lead-based perovskite-type oxide. Found to show. According to the present invention, a lead-free piezoelectric composite 1 having good piezoelectric performance can be provided.

  A Zn site (M site) of zinc oxide, which is a base oxide, includes a metal element having an ionic valence of 1 and a metal element having a valence of more than 2 having a piezoelectric property and a wurtzite structure. In the aspect using the zinc oxide-based wurtzite complex oxide (which may include inevitable impurities) contained in a proportion of 40 mol% or less in a range that can take up the total amount as a piezoelectric body 11, good insulation and piezoelectricity A lead-free piezoelectric composite 1 having characteristics can be provided.

"Piezoelectric element"
A piezoelectric element according to an embodiment of the present invention will be described with reference to the drawings. FIG. 8 is a schematic sectional view of the piezoelectric element 2. In order to facilitate visual recognition, the scale of each part is appropriately changed and shown.

  The piezoelectric element 2 includes a polymer composite piezoelectric film 1 made of the above-described piezoelectric composite of the present invention on a substrate 30 and a pair of electrodes for taking out charges generated when the polymer composite piezoelectric film 1 is distorted by receiving external force. (21, 22).

  The substrate 30 is preferably a film-like flexible substrate having a film thickness of 200 μm or less that does not impair the flexibility of the piezoelectric composite. Examples of such a substrate include polyimide, PTFE, polyethylene naphthalate, polypropylene, polystyrene, polycarbonate, polysulfone, polyarylate, polyamide, and the like, which can be selected depending on the usage environment of the piezoelectric element 2 depending on heat resistance and moisture absorption. it can. Further, by using a metal foil as the substrate 30, the lower electrode can also be used. Examples of such metal foil include aluminum, copper, stainless steel, nickel, tantalum and the like.

  The electrodes 21 and 22 are not particularly limited as long as the charges generated in the polymer composite piezoelectric film 1 can be suitably taken out. For example, Sn, Al, Ni, Pt, Au, Ag, Cu, Cr, Mo, etc. are mentioned. The film thickness of the electrodes 21 and 22 is not particularly limited as long as the flexibility of the piezoelectric composite is not impaired as in the case of the substrate 30. Although it depends on the size of the electrodes 21 and 22, it is preferably 10 μm or less. Such an electrode can be formed by a vapor deposition method such as a vacuum evaporation method or a sputtering method, a screen printing method and an ink jet method, a conductive paste, or a printing method using a conductive organic material.

  The film formation method of the polymer composite piezoelectric film 10 is not particularly limited, and may be formed by a solution film formation method such as a casting method, a melt film formation method such as a T-die film formation, or a printing method such as screen printing or an ink jet method. Can be membrane.

  In the case of the solution film forming method, when the piezoelectric body 11 included in the polymer composite piezoelectric film 10 has an anisotropic shape such as a whisker shape or a fiber shape, The major axis direction of the piezoelectric body 11 can be easily oriented. Further, when the piezoelectric bodies 11 are plate-like particles, they can be easily arranged regularly in the thickness direction.

  Further, in the method such as screen printing or ink jet printing, the polymer piezoelectric film 10 can be formed by patterning.

  As already described, the polymer composite piezoelectric film 10 is preferably subjected to polarization treatment. By adopting a configuration in which the anisotropic piezoelectric body 11 is oriented in a certain direction as described above, the high piezoelectric performance (d constant) using the orientation described in the embodiment of the piezoelectric composite can be obtained. preferable. The method for the polarization treatment is not particularly limited, and examples thereof include a normal polarization method in which an electric field is applied to the polymer composite piezoelectric film 10 in the film thickness direction, corona polarization, and the like.

  The piezoelectric element 2 is configured to include the piezoelectric composite 1 of the present invention. Accordingly, the same effect as that of the piezoelectric composite 1 can be obtained. The piezoelectric element 2 includes various sensors such as an ultrasonic sensor, a pressure sensor, a tactile sensor, and a strain sensor, an ultrasonic probe, an ultrasonic transducer such as a hydrophone, a vehicle, a building, and sports equipment such as a ski and a racket. It can be suitably used as a vibration power generation device (damper) used in the above, and a vibration power generation device used by applying to a floor, shoes, tires, or the like.

  In this embodiment, the case where the piezoelectric composite has a film shape that makes the most of its flexibility has been described as an example, but the present invention is not limited to the film shape.

  Embodiments according to the present invention will be described.

Example 1
First, vanadium-doped zinc oxide (V-ZnO) was prepared so as to have a composition of Zn _0.975 V _0.025 O (V2.5 at%). Zinc acetate dihydrate (Zn (CH ₃ C0O) ₂ · 2H ₂ O) and vanadium trichloride (VCl ₃ ) are weighed to the above composition so that the molar concentration is 0.1 M in 500 mL of ethylene glycol. And dissolved by stirring. The dissolved V—ZnO solution was heated at 200 ° C. for 2 hours to precipitate V—ZnO.

The precipitated V-ZnO was collected by centrifugation, washed with ethanol and water, and then heat-treated at 250 ° C for 1 hour to obtain a V-ZnO (Zn _0.975 V _0.025 O) raw material powder.

  Cyanoethylated PVA (CR-V manufactured by Shin-Etsu Chemical Co., Ltd.) is dissolved in a solvent (DMF) at a ratio of 30% by mass to prepare a mixed solution (CR-V solution). The powder was stirred and mixed at a rate of 2.0 g to make a paste, and a V-ZnO paste was obtained.

  Next, a sheet of V-ZnO paste is formed on a 0.3 mm thick aluminum substrate by a casting method to a thickness of 150 to 200 μm, and this aluminum substrate is heated and dried at a temperature of 120 ° C. on a hot plate. DMF was volatilized. As a result, a piezoelectric composite having a thickness of 70 μm formed on the aluminum substrate and a V-ZnO powder integration rate of 60% was obtained.

  Next, an upper electrode made of aluminum having a diameter of 15 mm and a thickness of 1 μm is formed on the piezoelectric composite by a vacuum deposition method to obtain a piezoelectric element, and then the upper electrode-aluminum is heated while heating the aluminum substrate to a temperature of 100 ° C. A polarization treatment was performed by applying DC 2 kV for 10 minutes between the substrates (lower electrodes).

The piezoelectric element was cut to a size of 20 mm square with the upper electrode as the center, and the d ₃₃ value was measured using a piezoelectric evaluation apparatus PM-300 manufactured by PIEZO TEST. The d ₃₃ value measurement conditions were a frequency of 110 Hz, a clamping force of 10 N, and a dynamic force of 0.25 N.

As a result of the measurement, the piezoelectric element obtained had a d ₃₃ value of d ₃₃ = 40 (pC / N), and good piezoelectric characteristics were obtained.

(Comparative Example 1)
A comparative piezoelectric element was prepared in the same manner as in Example 1 except that the piezoelectric powder was non-doped ZnO, and the d ₃₃ value was measured. The measurement result of the d ₃₃ value was d ₃₃ = 5 (pC / N).

  The polymer composite piezoelectric material of the present invention includes various sensors such as an ultrasonic sensor, a pressure sensor, a tactile sensor, and a strain sensor, an ultrasonic probe, an ultrasonic transducer such as a hydrophone, a vehicle, a building, a ski, and a racket. It can be preferably used as a vibration damping device (damper) used for sports equipment such as, and a vibration power generator used by applying to floors, shoes, tires and the like.

1,1a, 1b Polymer composite piezoelectric material (piezoelectric composite, polymer composite piezoelectric material film)
2 Piezoelectric element 11a, 11b Piezoelectric body 12a, 11b Organic polymer resin 21, 22 Electrode 30 Substrate

Claims (14)

An organic polymer resin;
Including a plurality of piezoelectric bodies dispersed in the organic polymer resin;
The piezoelectric composite is composed of a wurtzite complex oxide having a composition represented by the following general formula ( PY ) (may contain inevitable impurities).
Zn _x (A _y , B _z , C _w ) O (PY)
(In the formula (PY), 0.6 ≦ x <1, 0 <y, 0 ≦ z, 0 <w,
A: M site element having a monovalent ionic valence, and at least one metal element selected from the group consisting of Li, Na, and K. B: M-site element having an ionic valence of 2 and at least one metal element selected from the group consisting of Be, Mg, Ca, Ni, Sr, and Ba. C: M site element having an average ion valence greater than divalent, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Nb, Mo, Ta, and And at least one metal element selected from the group consisting of W. )   2. The polymer composite piezoelectric material according to claim 1, wherein a difference between a dielectric constant of the wurzeite complex oxide and a dielectric constant of the organic polymer resin is within 50%.   3. The polymer composite piezoelectric material according to claim 2, wherein a difference between a dielectric constant of the wurtzite complex oxide and a dielectric constant of the organic polymer resin is within 10%.   The polymer composite piezoelectric material according to claim 1, wherein the organic polymer resin has a dielectric constant of 7 or more.   Each of the plurality of piezoelectric bodies has crystal orientation, and is arranged in such a manner that the polarization directions of the plurality of piezoelectric bodies are substantially parallel and dispersed in the organic polymer resin. The polymer composite piezoelectric material according to any one of claims 1 to 4.   The polymer composite piezoelectric body according to claim 1, wherein the plurality of piezoelectric bodies have c-axis orientation.   The polymer composite piezoelectric material according to claim 1, wherein a volume fraction of the piezoelectric material in the organic polymer resin is 30% or more and 90% or less. The polymer composite piezoelectric material according to claim 1, wherein the piezoelectric material has a dielectric constant of 15 to 40 and a piezoelectric constant d ₃₃ of 50 pC / N or more. The polymer composite piezoelectric material according to claim 1, wherein the piezoelectric constant d ₃₃ is 30 pC / N or more.   The polymer composite piezoelectric material according to claim 1, wherein the piezoelectric material has a particle shape and has 0-3 type connectivity.   10. The polymer composite piezoelectric body according to claim 1, wherein the piezoelectric body has a columnar shape and has 1-3 type connectivity. Polymer composite piezoelectric body according to any one of claims 1 to 11, wherein the element A is Li or Na. Polymer composite piezoelectric body according to any one of claims 1 to 12, characterized in that a polymer composite piezoelectric film. A piezoelectric element comprising the polymer composite piezoelectric body according to any one of claims 1 to 13 and a pair of electrodes that sandwich the piezoelectric body.