JP2010030832A - Piezoelectric ceramic and piezoelectric element using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic being excellent in heat resistance and having high traverse rupture strength and to provide a piezoelectric element. <P>SOLUTION: The piezoelectric ceramic is characterized by containing at least one kind selected from among Mn, Co and Cu by 0.1-1 pt.mass in terms of total oxides to a main component of 100 pt.mass in a bismuth layered compound having a compositional formula denoted as Bi<SB>4</SB>(Ti<SB>1-γ</SB>Zr<SB>γ</SB>)<SB>3</SB>O<SB>12</SB>-α[(1-β)M1(Ti<SB>1-γ</SB>Zr<SB>γ</SB>)O<SB>3</SB>-βM2M3O<SB>3</SB>] (wherein, α, β and γ are satisfied with 0.3≤α≤0.95, 0≤β≤0.5 and 0.01≤γ≤0.3; M1 is at least one kind selected from among Sr, Ba, Ca, (Bi<SB>0.5</SB>Na<SB>0.5</SB>), (Bi<SB>0.5</SB>Li<SB>0.5</SB>) and (Bi<SB>0.5</SB>K<SB>0.5</SB>); M2 is at least one kind selected from among Bi, Na, K and Li; and M3 is at least one kind selected from among Fe and Nb). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic and a piezoelectric element using the piezoelectric ceramic, and is suitable for a resonator, an ultrasonic vibrator, an ultrasonic motor, an acceleration sensor, a knocking sensor, an AE sensor, and the like. The present invention relates to a piezoelectric ceramic suitably used as a used piezoelectric sensor and a piezoelectric element using the piezoelectric ceramic.

  Examples of products using a piezoelectric ceramic include a piezoelectric sensor, a filter, a piezoelectric resonator, an ultrasonic vibrator, and an ultrasonic motor.

  The piezoelectric sensor is used as a shock sensor, an acceleration sensor, or an in-vehicle knocking sensor. Particularly in recent years, a pressure sensor for directly detecting the pressure in the cylinder and optimizing the fuel injection timing from the injector in order to improve the fuel efficiency of the automobile engine and reduce the exhaust gas (HC, NOx). As a research.

  Here, a mechanism for detecting a pressure change in the cylinder will be described. The pressure is constituted by, for example, a pressure transmission pin protruding into a cylinder of the engine and a piezoelectric sensor that detects a pressure change in the cylinder transmitted through the pressure transmission pin. In order to transmit the pressure in the cylinder of this pressure transmission pin, a part of its tip protrudes into the cylinder, and that part is exposed to the high temperature during combustion in the cylinder, so the piezoelectric sensor connected to the pressure transmission pin The heat is transferred with a high pressure change, and the temperature reaches 150 ° C.

  Conventionally, PZT (lead zirconate titanate) -based materials and PT (lead titanate) -based materials having high piezoelectricity and a large piezoelectric constant d have been used as piezoelectric ceramics.

  However, it has been pointed out that PZT and PT-based materials contain about 60% by mass of lead, so that lead elution occurs due to acid rain and there is a risk of causing environmental pollution.

In addition, since PZT materials and PT materials have a Curie temperature _Tc of about 200 to 300 ° C., the piezoelectric constant d deteriorates when used at a high temperature of about 150 ° C., compared to the piezoelectric constant d at room temperature. In view of the large change in the piezoelectric constant d at 150 ° C. Therefore, when a piezoelectric material made of PZT material or PT material is used as a pressure sensor for directly detecting the pressure in the engine cylinder, for example, when it is exposed to a high temperature of 150 ° C., the piezoelectric constant d Since the output voltage changes even when the same pressure is applied, the change in the piezoelectric constant d at 150 ° C. with respect to the piezoelectric constant d at room temperature is large. Thus, it was difficult to calculate an accurate pressure from the output voltage.

  In contrast, in order to obtain stable characteristics as a pressure sensor even at a high temperature of 150 ° C., studies using single crystals such as langasite and quartz have been made. However, in the case of a single crystal, there is a problem that the piezoelectric constant d is small. Further, chipping is likely to occur during processing, it is easy to crack, and it is easy to crack when pressure is applied during actual use. Furthermore, there is a problem that the manufacturing cost of the single crystal is extremely high.

  Therefore, high expectations are placed on piezoelectric materials that do not contain lead.

As a piezoelectric ceramic not containing lead, a material mainly composed of a bismuth layered compound has been proposed (for example, Patent Document 1). Piezoelectric ceramics mainly composed of bismuth layered compounds often have a Curie temperature of about 400 ° C or higher. Such a ceramic has high heat resistance and is exposed to high temperatures such as in an engine room. It may be applicable as a piezoelectric element used in
JP 2002-167276 A

  However, in the piezoelectric ceramic mainly composed of the bismuth layered compound described in Patent Document 1, there are cases where the ceramic is cracked or chipped in the manufacturing process of the piezoelectric ceramic, the process of incorporating the piezoelectric ceramic into the device, or the like.

  Accordingly, an object of the present invention is to provide a piezoelectric ceramic and a piezoelectric element that are excellent in heat resistance and have high bending strength.

The piezoelectric ceramic of the present invention has a composition formula expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ]. 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3, and M1 is Sr, Ba, Ca, (Bi _0.5 Na _{0. 5} ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), and M2 is at least one selected from Bi, Na, K and Li. There, M3 is, with respect to the main component of 100 parts by weight of the bismuth layered compound is at least one selected from Fe and Nb, Mn, oxide of at least one selected from Co and Cu _(MnO 2, CoO, CuO ₂ ) 0.1 to 1 parts by mass in terms of total conversion And

In addition, the piezoelectric ceramic is provided in 100 parts by mass of the main component of the bismuth layered compound that satisfies 0.4 ≦ α ≦ 0.7, 0 ≦ β ≦ 0.3, and 0.1 ≦ γ ≦ 0.2 in the composition formula. On the other hand, it is preferable to contain at least one selected from Mn, Co and Cu in an amount of 0.1 to 0.5 parts by mass in terms of oxide (MnO ₂ , CoO, CuO ₂ ).

  Moreover, it is preferable that 0.1 ≦ β.

  The piezoelectric element of the present invention is characterized in that electrodes are provided on a pair of opposing surfaces of a base body made of the piezoelectric ceramic.

According to the piezoelectric ceramic of the present invention, the composition formula is expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ] When satisfying 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3, M1 is Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), and M2 is at least 1 selected from Bi, Na, K and Li a species, M3 is, with respect to the main component of 100 parts by weight of the bismuth layered compound is at least one selected from Fe and Nb, Mn, oxide of at least one selected from Co and Cu _(MnO 2, CoO And 0.1 to 1 parts by mass in total in terms of CuO ₂ ) Thus, the heat resistance is excellent, the bending strength of the piezoelectric ceramic is increased, and it is difficult to break against stress.

In addition, the piezoelectric ceramic is provided in 100 parts by mass of the main component of the bismuth layered compound that satisfies 0.4 ≦ α ≦ 0.7, 0 ≦ β ≦ 0.3, and 0.1 ≦ γ ≦ 0.2 in the composition formula. On the other hand, when at least one selected from Mn, Co, and Cu is contained in an amount of 0.1 to 0.5 parts by mass in terms of oxide (MnO ₂ , CoO, CuO ₂ ), the hysteresis described later may be lowered. it can.

Further, when 0.1 ≦ β, a piezoelectric ceramic having stable piezoelectric characteristics can be obtained in which the variation in the dynamic piezoelectric constant d ₃₃ described later is small even when the firing temperature varies.

  In addition, according to the piezoelectric element of the present invention, the electrodes are provided on a pair of opposed surfaces of the substrate made of the piezoelectric ceramic. Since the piezoelectric element of the present invention is a polycrystal, it does not have the property of being easily cracked on a specific surface like a single crystal, and chipping and other chipping are less likely to occur, resulting in fewer defects due to them and yield. Can be obtained.

The piezoelectric ceramic of the present invention has a composition formula expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ]. 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3, and M1 is Sr, Ba, Ca, (Bi _0.5 Na _{0. 5} ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), and M2 is at least one selected from Bi, Na, K and Li. There, M3 is, with respect to the main component of 100 parts by weight of the bismuth layered compound is at least one selected from Fe and Nb, Mn, oxide of at least one selected from Co and Cu _(MnO 2, CoO, CuO ₂ ) Containing 0.1 to 1 part by mass in terms of conversion .

The bending strength of the piezoelectric ceramic can be increased by setting the substitution amount γ of Zr to 0.01 ≦ γ ≦ 0.3. If γ is smaller than 0.01, the bending strength is lowered. On the other hand, if γ is larger than 0.3, the bending strength increases, but the volume resistivity decreases. It is preferable that γ satisfies 0.1 ≦ γ ≦ 0.2 in that the hysteresis described later can be reduced and the dynamic piezoelectric constant d ₃₃ described later can be increased.

Here, the output charge generated by the piezoelectric effect and its hysteresis will be described. The output charge generated by the positive piezoelectric effect can be measured using, for example, the apparatus shown in FIG. This apparatus applies a load F _low to the piezoelectric element 5 having electrodes 2a and 2b formed on the upper and lower surfaces of the plate-like piezoelectric ceramic 1, and then increases the load applied to the piezoelectric element 5 to F _high. , Repeatedly returning to F _low , and measuring the output charge Q generated in the piezoelectric element 5 during that time with a charge amplifier. The load at this time is, for example, a 10 Hz triangular wave with F _low = 250 N and F _high = 300 N give.

The relationship between the load measured in this way and the output charge is shown in a graph, for example, as shown in FIG. The arrow in the graph indicates whether the measured value is measured when increasing the load or measured when decreasing the load. In FIG. 2, the output charge measured as the applied load increases is lower. The output charge at the load F _low is Q ₀ , the output charge at the load F _mid (= (F _low + F _high ) / 2) when the load is increasing is Q ₁ , and the output charge at the load F _high is Q _2, the output charge of a load F _mid when the load is getting low as Q _3. Q ₁ and Q ₃ do not match, and this difference is hysteresis. Thereafter, the value of (Q ₃ −Q ₁ ) / (Q ₂ −Q ₀ ) is used as an index of hysteresis and is simply referred to as hysteresis. The hysteresis value is preferably 1% or less, particularly preferably 0.5% or less. The hysteresis basically has a value of 0 or more.

Next, the dynamic piezoelectric constant d ₃₃ will be described. The dynamic piezoelectric constant d ₃₃ is a piezoelectric constant d ₃₃ measured by an expression described later using an actual measurement value of an output voltage when a load is directly applied to the piezoelectric element 5. Conventionally, the piezoelectric constant d ₃₃ has been measured using the resonance impedance method. However, since the load applied to the piezoelectric element 5 is small in this method, the dynamic characteristics cannot be evaluated when an actual load is applied. Therefore, the piezoelectric constant d ₃₃ (= output charge / load change) was measured from the relationship between the load when the actual load was applied and the output charge, and this was defined as the dynamic piezoelectric constant d ₃₃ .

The specific measuring apparatus and measurement are the same as in the case of the hysteresis measurement described above. For example, first, an offset load of 250N is applied to the piezoelectric element 5, and a load of 50N is applied in a triangular waveform in addition to the offset load. An output charge Q with respect to a peak load 50N of the triangular wave applied to the piezoelectric element 5 is measured by a charge amplifier. From the relationship of the output charge Q with respect to the application of 50 N load, the dynamic piezoelectric constant d ₃₃ is d ₃₃ = Q / 50 N (amount of change in load). That is, the dynamic piezoelectric constant d ₃₃ is a unit C (Coulomb) / N, and means the piezoelectric constant d ₃₃ in a dynamic state when a load is applied to the piezoelectric element.

  The reason why the offset load of 250 N is applied is to obtain a stable output characteristic by preventing the tensile force from acting on the piezoelectric element 5. The load change amount is set to 50 N, for example, as an application example, a range necessary for detecting a pressure change in the engine cylinder.

In the piezoelectric ceramic of the present invention, when expressed by the composition formula as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ] The reason why the range of 0.3 ≦ α ≦ 0.95 is set is that when α is smaller than 0.3, the dynamic piezoelectric constant d ₃₃ is lower than 15 pC / N, and α is larger than 0.95. If it is because the dynamic piezoelectric constant d ₃₃ temperature rate of change at -40 ℃ and 0.99 ° C. for dynamic piezoelectric constant d ₃₃ at 25 ° C. is greater than 5% ±. Further, it is preferable that 0.4 ≦ α ≦ 0.95 in view of increasing the dynamic piezoelectric constant d _33, and it is particularly preferable that 0.4 ≦ α ≦ 0.7.

M1 is, Sr, when at least one of Ba and Ca, the higher the molar ratio of Sr occupying the M1, preferred because it increased dynamic piezoelectric constant d _33. A high molar ratio of Ba in M1 is preferable because hysteresis can be reduced, and Ba in M1 is preferably 20 mol% or more, particularly preferably 40 mol% or more. A high molar ratio of Ca to M1 is preferable because the linearity of change in the dynamic piezoelectric constant d _{33 with} respect to temperature is improved. Also preferred for the molar ratio of the total amount of Ba and Ca occupies the M1 is the temperature dependence of the high dynamic piezoelectric constant d ₃₃ becomes lower.

Further, when M1 contains at least one of (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), the piezoelectric ceramic is sintered. Sexuality is improved. The sinterability is higher as the molar ratio of the total amount of (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ) in M1 is higher. Get better. Since (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ), and (Bi _0.5 K _0.5 ) are bivalent on average, they can be arbitrarily selected from Sr, Ba, and Ca. It can be used by mixing at a ratio of

Increasing the dynamic piezoelectric constant d _33, that in order to lower the temperature dependency of the dynamic piezoelectric constant d ₃₃ is, M1 is _{Sr δ Ba (1-δ)} , which is 0.2 ≦ δ ≦ 0.8 Is preferred.

M2 of M2M3O ₃ is at least one kind of element selected Bi, Na, K and Li, M3 is at least one selected from Fe and Nb. The reason why the substitution amount β of M2M3O ₃ is set to 0 ≦ β ≦ 0.5 is that when β is larger than 0.5, the dynamic piezoelectric constant d ₃₃ decreases. M2M3O ₃ has the effect of extending the stable range of firing temperature obtained characteristics (stable firing temperature range). The stable firing temperature range is about 10 ° C. when β <0.1, but by setting 0.1 ≦ β ≦ 0.5, the stable firing temperature range can be reduced without significantly reducing the dynamic piezoelectric constant d _33. It can be extended to 20-40 ° C. In that widen the stable firing temperature range, M2M3O ₃ is particularly preferably from BiFeO _3. In order to further reduce the hysteresis, it is preferable that β ≦ 0.3.

Next, it is contained with respect to 100 parts by mass of the aforementioned Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ] component. The amount of Mn, Co and Cu will be described. When the content of Mn in terms of MnO ₂ is less than 0.1 parts by mass with respect to the above components, since this material system is a plate-like crystal, it is difficult to sinter, and it is difficult to obtain a dense porcelain and elastic. Since the loss increases, the dynamic piezoelectric constant d ₃₃ becomes smaller than 15 pC / N. On the other hand, when the amount is more than 1 part by mass, although it is easy to sinter, a heterogeneous phase is easily formed and the volume resistivity is lowered. The content of Mn in terms of MnO ₂ is preferably 0.5 parts by mass or less in that hysteresis can be reduced.

Further, Co contained in 100 parts by mass of the aforementioned Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ] component. Similarly, when the Co content is less than 0.1 parts by mass in terms of CoO, the material system is a plate-like crystal, making it difficult to sinter, making it difficult to obtain dense porcelain and elastic loss. Therefore, the dynamic piezoelectric constant d ₃₃ becomes smaller than 15 pC / N. On the other hand, when the amount is more than 1 part by mass, it becomes easy to sinter, but a heterogeneous phase is easily formed, and the volume resistivity is lowered. The content of Co in terms of CoO is preferably 0.5 parts by mass or less in that hysteresis can be reduced.

Furthermore, Cu contained with respect to 100 parts by mass of the aforementioned Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ] component. Similarly, when the Cu content is less than 0.1 parts by mass in terms of CuO ₂ , the material system is a plate-like crystal, which makes it difficult to sinter, making it difficult to obtain dense porcelain and elastic. Since the loss increases, the dynamic piezoelectric constant d ₃₃ becomes smaller than 15 pC / N. On the other hand, when the amount is more than 1 part by mass, the temperature change rate of the dynamic piezoelectric constant d ₃₃ at 150 ° C. exceeds ± 5% with respect to the dynamic piezoelectric constant d _{33 at} 25 ° C. The content of Cu in terms of CuO ₂ is preferably 0.5 parts by mass or less from the viewpoint that hysteresis can be reduced.

Furthermore, the same applies when a plurality of elements selected from Mn, Co, and Cu are contained, and the content is 0.1 to 1 part by mass in terms of oxide (Mn ₂ O ₃ , CoO, CuO ₂ ). The total is particularly preferably 0.5 parts by mass or less in that the hysteresis can be reduced. Of Mn, Co, and Cu, Co and Mn are preferable in that the dynamic piezoelectric constant d ₃₃ can be increased, and Co is particularly preferable.

As described above, when the composition formula is expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ · βM ₂ M ₃ O ₃ ], .4 ≦ α ≦ 0.7, 0 ≦ β ≦ 0.3, 0.1 ≦ γ ≦ 0.2, and at least 1 selected from Mn, Co and Cu with respect to 100 parts by mass of the main component of the bismuth layered compound In a piezoelectric ceramic containing 0.1 to 0.5 parts by mass of seeds in terms of oxide (MnO ₂ , CoO, CuO ₂ ) in total, the hysteresis can be reduced to 0.5% or less.

In the piezoelectric ceramic of the present invention, the composition formula of the main component is Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M ₁ (Ti _1-γ Zr _γ ) O ₃ .βM2M ₃ O ₃ ]. The main crystal phase is composed of a bismuth layered compound. Basically, a part of M1 constituting a suspected perovskite layer of a bismuth layered compound represented by Bi ₄ Ti ₃ O ₁₂ · αM1TiO ₃ is replaced with M2, and a part of Ti is replaced with Zr or M3. It is thought that. That is, the piezoelectric ceramic according to the present invention includes an α site, a β site, and an oxygen site in a general formula of a bismuth layered structure represented by (Bi ₂ O ₂ ) ²⁺ (α _m−1 β _m O _{3m + 1} ) ^2−. The composition phase boundary MPB (Morphotoropic Phase Boundary) where the tetragonal crystal generated when m = 4 and the orthorhombic crystal generated when m = 3 are mixed by adjusting the type and amount of the constituent elements coordinated to A possessed bismuth layered structure can be obtained. As a result, a characteristic piezoelectric characteristic in the vicinity of the MPB composition, which is also known in PZT, can be realized in the bismuth layered compound.

  In addition, at least one selected from Mn, Co and Cu contained therein is solid-solved in the main crystal phase, and a part thereof is a crystal of a compound containing at least one selected from Mn, Co and Cu. In some cases, it may precipitate at the grain boundaries, and as other crystal phases, there may be a pyrochlore phase, a perovskite phase, or a bismuth layered compound having a different structure.

In addition, when Zr is not added at the time of blending, Zr may be mixed from the ZrO ₂ balls at the time of pulverization, but the amount is on the order of 10 ⁻⁶ mass%. There is no improvement in folding strength.

The piezoelectric ceramic of the present invention includes, for example, SrCO ₃ , BaCO ₃ , CaCO ₃ , Nb ₂ O ₅ , Bi ₂ O ₃ , TiO ₂ , Na ₂ CO ₃ , K ₂ CO ₃ , Li ₂ CO ₃ , Fe as raw materials. Various oxides or salts thereof composed of ₂ O ₃ , ZrO ₂ , MnO ₃ , CoO and CuO ₂ can be used. A raw material is not limited to this, You may use metal salts, such as carbonate and nitrate which produce | generate an oxide by baking.

When these raw materials are expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M1 (Ti _1-γ Zr _γ ) O ₃ · βM2M3O ₃ ], 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3, and M1 is Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _{0 .5} Li _0.5) and _(at least one selected from Bi _{0.5 K 0.5),} M2 is at least one selected Bi, Na, K and Li, M3 is, Fe And 100 parts by mass of the main component of the bismuth layered compound which is at least one selected from Nb, at least one selected from Mn, Co and Cu in terms of oxide (MnO ₂ , CoO, CuO ₂ ) Weigh so as to contain 0.1 to 1 part by mass. The powder weighed and mixed is pulverized so that the average particle size distribution (D ₅₀ ) is in the range of 0.5 to 1 μm, this mixture is calcined at 800 to 1050 ° C., and a predetermined organic binder is added and wet mixed. Then granulate. The powder thus obtained is molded into a predetermined shape by known press molding or the like, and baked in an oxidizing atmosphere such as the air at a temperature range of 1050 to 1250 ° C. for 2 to 5 hours. Is obtained.

  The piezoelectric ceramic of the present invention is suitable as a piezoelectric ceramic for a pressure sensor as shown in FIG. 3 or a piezoelectric ceramic for a shock sensor as shown in FIG. 4, but other piezoelectric resonators and ultrasonic transducers are used. It can be used for piezoelectric sensors such as ultrasonic motors, knocking sensors, and AE sensors.

  FIG. 3 shows a piezoelectric element 5 according to an embodiment of the present invention. The piezoelectric element 5 is configured by forming electrodes 2a and 2b on a pair of opposed surfaces of a cylindrical substrate 1 made of the above-described piezoelectric ceramic. In FIG. 3, the electrodes 2 a and 2 b are formed on the entire circular surface that is the upper and lower surfaces of the substrate 1. The polarization is applied in the thickness direction of the substrate 1 indicated by the arrow 4. Such a piezoelectric element 5 is stable without being destroyed even when a high load of 500 N is applied at a high temperature of 150 ° C., for example, when it is used for an application for directly detecting the pressure in the engine cylinder of an automobile. Works. According to the stress analysis by simulation, even when a load of 500 N was applied, the maximum principal stress generated in the piezoelectric element 5 was about 1/10 or less of the mechanical strength of the piezoelectric ceramic constituting the substrate 1.

  FIG. 4 shows a shock sensor 17 using a piezoelectric element 15 according to an embodiment of the present invention. The piezoelectric element 15 is formed by laminating flat bases 11a and 11b made of the above-described piezoelectric ceramic, electrodes 12a and 12b are formed on a pair of opposing surfaces of the base 11a, and electrodes 12b on a pair of opposing surfaces of the base 11b. , 12c are formed. Further, the polarization is applied in the same direction as the thickness direction of the bases 11a and 11b indicated by an arrow 14. One end of the piezoelectric element 15 is fixed by a fixing portion 16, and becomes a shock sensor 17 as a whole. When a shock (acceleration) is applied to the shock sensor 17 from the outside, the other end of the piezoelectric element 15 is displaced with respect to the fixed portion 16, and the charge generated in the piezoelectric element 15 bent in the stacking direction is transferred to the electrode 12b. The acceleration applied to the shock sensor 17 can be measured by measuring the potential difference between the electrodes 12a and 12c.

  Such a shock sensor 17 can also be manufactured by using a PZT-based piezoelectric ceramic. However, since the bending strength of the PZT-based piezoelectric ceramic is about 80 MPa even when the bending strength is high, a large acceleration is applied due to dropping or the like. A metal plate is used for the electrode 12b or the like so as not to break. If the electrode 12b is a metal plate, there is a problem that the sensitivity of the piezoelectric element is lowered or the element is enlarged.

  On the other hand, in a piezoelectric ceramic having a bending strength of 200 MPa or more like the piezoelectric ceramic of the present invention, a sintered conductor such as Ag / Pd can be used as the electrodes 12a, 12b, 12c, and it is small and sensitive and breaks. A pile shock sensor 17 can be produced. For example, the substrate 11a, 11b is composed of two layers using a portion to be sensed, that is, a portion of the portion bent from the fixed portion 16 having a length of 1.0 mm × width of 0.21 mm × thickness of 30 μm. A bimorph shock sensor 17 can be manufactured. Such a shock sensor 17 is mounted on, for example, a hard disk and can be used as a sensor for measures against dropping impact.

  The reliability test of the shock sensor 17 with respect to the drop impact is performed by mounting the shock sensor 17 on a circuit board of, for example, a 2.5 inch hard disk and dropping it naturally on the concrete from a height of 1.5 m. In the case of a piezoelectric ceramic whose bending strength is lower than 200 MPa, if the drop test is performed 10 times, a part of the piezoelectric ceramic is broken or cracked, and inspecting the sensor characteristics after the drop test causes problems such as spurious characteristics. Many things happened. On the other hand, when the bending strength of the piezoelectric ceramic is 200 MPa or more, the occurrence of cracks and changes in characteristics are hardly observed, and the defect occurrence probability by Weibull evaluation can be reduced to 1 ppm or less.

First, SrCO ₃ powder having a purity of 99.9%, BaCO ₃ powder, CaCO ₃ powder, Bi ₂ O ₃ powder, TiO ₂ powder, Nb ₂ O ₅ powder, Na ₂ CO ₃ powder, K ₂ CO ₃ powder as starting materials , Li ₂ CO ₃ powder, Fe ₂ O ₃ powder, and ZrO ₂ powder are expressed by a molar ratio of Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M1 (Ti _1-γ when expressed as _{Zr γ) O 3 · βM2M3O 3} ], M1, M2, M3, α, β, γ were weighed so that the elements shown in Table 1 and Table 2, the ratio.

With respect to 100 parts by weight of the main component, MnO ₂ powder, CoO powder and CuO ₂ powder are weighed and mixed so as to have the weight parts shown in Tables 1 and 2, and zirconia balls having a purity of 99.9% and water Alternatively, it was put into a 500 ml resin pot together with isopropyl alcohol (IPA), and the resin pot was placed on a turntable and mixed for 16 hours.

The mixed slurry is dried in the air, passed through a # 40 mesh, and then calcined by holding at 950 ° C. for 3 hours in the air, and this synthetic powder is mixed with ZrO ₂ balls having a purity of 99.9% and water or isopropyl. The mixture was poured into a 500 ml resin pot together with alcohol (IPA), and the resin pot was placed on a rotating table and ground for 20 hours.

An appropriate amount of an organic binder is added to the pulverized powder and granulated, and a cylindrical shaped body is produced with a mold press at a load of 150 MPa, and then the binder is removed. Firing was performed under conditions of 3 hours at a peak temperature at which the dynamic piezoelectric constant d ₃₃ of each sample was highest between 1250 ° C. to obtain a disk-shaped piezoelectric ceramic having a diameter of 4 mm and a thickness of 2 mm. In addition, a piezoelectric ceramic that was fired by changing the firing peak temperature at intervals of 5 ° C. in the range of −30 to + 30 ° C. with respect to the firing peak temperature at which the dynamic piezoelectric constant d ₃₃ was the highest was also produced.

  Thereafter, Ag electrodes were baked on both main surfaces of the cylindrical piezoelectric ceramic, and a polarization treatment was performed by applying a DC voltage of 5 kV / mm or more in the thickness direction at 200 ° C., and then 300 ° C. The heat aging treatment was performed for 24 hours.

  In addition, test pieces for measuring the bending strength were produced in the same manner as described above, and the bending strength was evaluated by a four-point bending method in accordance with JIS R1606.

The dynamic piezoelectric constant d ₃₃ and hysteresis at room temperature (25 ° C.) were evaluated using the apparatus shown in FIG. Specifically, first, an offset load of 250 N was applied to the piezoelectric element 5. Thereafter, the load applied to the piezoelectric element 5 was increased to 300N and then returned again to 250N, and the change in the amount of charge output from the piezoelectric element 5 was measured with a charge amplifier. The load at this time was given as a 10 Hz triangular wave. Then, the dynamic piezoelectric constant d ₃₃ was obtained from the equation: dynamic piezoelectric constant d ₃₃ = output charge / load variation (unit pC / N). Similarly, the dynamic piezoelectric constant d ₃₃ at −40 ° C. and 150 ° C. was measured, and the temperature change rate of the dynamic piezoelectric constant d ₃₃ was obtained. Temperature change rate of the dynamic piezoelectric constant d ₃₃ of from room temperature to T ° C. from a dynamic piezoelectric constant d ₃₃ in the dynamic piezoelectric constant d ₃₃ and T ° C. at room temperature (25 ° C.), the dynamic piezoelectric constant at (T ° C. d ₃₃ - was determined from the equation of room temperature (25 ° C.) dynamic piezoelectric constant d ₃₃ in) / (room temperature (25 ° C.) dynamic piezoelectric constant d ₃₃ in).

Moreover, volume specific resistance was evaluated based on JIS-C2141. The volume resistivity was 1 × 10 ⁹ Ω · m or more as good, and in Tables 1 and 2, ○ was less than 1 × 10 ⁹ Ω · m, and in Tables 1 and 2, it was shown as x. This is because the volume specific resistance of the piezoelectric element 5 is desired to be 1 × 10 ⁹ Ω · m or more in order to maintain the detection sensitivity at a high temperature of 150 ° C. Since the volume resistivity is higher than this, the output charge is suppressed from being consumed by the piezoelectric element 5 and is supplied to the signal processing circuit. The performance deterioration of the sensor characteristics is not caused.

Tables 1 and 2 show the results of the samples having the highest dynamic piezoelectric constant d ₃₃ while changing the firing peak temperature for each composition. Furthermore, a dynamic piezoelectric constant d ₃₃ of the sample changing the peak temperature of firing, the most dynamic piezoelectric constant as compared to the higher was the sample of d _33, decrease in dynamic piezoelectric constant d ₃₃ is within 5% baking The temperature range was examined, and the range was defined as the stable firing temperature range of each composition. When this temperature range is wide, a piezoelectric ceramic having stable piezoelectric characteristics can be produced with little fluctuation in the dynamic piezoelectric constant d ₃₃ when the firing temperature varies during the production.

As is apparent from Tables 1 and 2, the compositional formula, which is a piezoelectric ceramic within the scope of the present invention, is Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M1 (Ti ₁ when represented as _{-γ Zr γ) O 3 · βM2M3O} 3], along with satisfying 0.3 ≦ α ≦ 0.95,0 ≦ β ≦ 0.5,0.01 ≦ γ ≦ 0.3, M1 is , Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), and M2 is From Mn, Co and Cu with respect to 100 parts by mass of the main component of the bismuth layered compound, wherein M3 is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb At least one selected from oxides (MnO ₂ , CoO, CuO ₂ ) Sample No. containing 0.1 to 1 part by mass in terms of conversion. 3 to 10, 12 to 18, 20 to 22, 25 to 27, 29 to 32, 34 to 37, 39, 42 to 49, 51 to 54, 56 to 58, 60 to 62, 64 to 66, 68 and 69 are bending strength is as large as more than 207 MPa, the dynamic piezoelectric constant d ₃₃ has a higher 15.1pC / N, 25 -40 and 0.99 ° C. for dynamic piezoelectric constant d ₃₃ of ° C. dynamic piezoelectric constant d ₃₃ The change was within ± 4.98%, the volume resistivity was 1 × 10 ⁹ Ω · m or more, and the hysteresis was 0.99% or less.

In particular, in the composition formula, Mn with respect to 100 parts by mass of the main component of the bismuth layered compound satisfying 0.4 ≦ α ≦ 0.7, 0 ≦ β ≦ 0.3, and 0.1 ≦ γ ≦ 0.2. Sample No. containing at least one selected from Co, Cu and 0.1 to 0.5 parts by mass in terms of oxide (MnO ₂ , CoO, CuO ₂ ). 4-9, 12-18, 21, 25, 26, 29-31, 34-36, 39, 43-47, 51-54, 57, 60, 61, 64, 65, 68 and 69 have zero hysteresis .5% or less.

  In addition, the sample No. Nos. 42 to 49, 51 to 54, 56 to 58, 60 to 62, 64 to 66, 68 and 69 had a stable firing temperature range of 25 ° C. or more.

On the other hand, when expressed by the composition formula, 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3 is satisfied, and M1 is Sr, At least one selected from Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), and M2 is Bi, At least one selected from Na, K and Li, and M3 is at least one selected from Mn, Co and Cu with respect to 100 parts by mass of the main component of the bismuth layered compound selected from Fe and Nb. Sample No. 1 outside the scope of the present invention does not satisfy any of the conditions that one type is contained in an amount of 0.1 to 1 part by mass in terms of oxide (MnO ₂ , CoO, CuO ₂ ). 1, 2, 11, 19, 23, 24, 28, 33, 38, 40, 41, 50, 55, 59, 63, 67 and 70, the bending strength is 183 MPa or less, or the dynamic piezoelectric constant d ₃₃ was 14.8 pC / N or less, or the change in the dynamic piezoelectric constant d ₃₃ at −40 and 150 ° C. with respect to the dynamic piezoelectric constant d _{33 at} 25 ° C. was greater than ± 5.5%.

FIG. 1 (α = 0), No. 1 6 (α = 0.45) and no. 11 (α = 01) is a result of X-ray diffraction, and FIG. 6 is an enlarged view of 2θ = 32 to 34 ° in FIG. 5. It can be seen that each sample has a bismuth layered compound as the main crystal phase. The crystal when α = 0 is an orthorhombic crystal (a-axis length ≠ b-axis length), and the crystal when α = 1 is square. It was a crystal (a-axis length = b-axis length). In the range of 0.3 ≦ α ≦ 0.95, tetragonal crystals and orthorhombic crystals are mixed, and in particular, in the range of 0.4 ≦ α ≦ 0.5, the composition phase boundary MPB is obtained. . This MPB is well known as a PZT piezoelectric material, and the MPB is formed in a composition region in which the rhombohedral crystal of PZ and the tetragonal crystal of PT are in a ratio of approximately 1: 1. In the vicinity of the MPB of this PZT, the piezoelectric constant d shows the maximum value, and the temperature coefficient of the piezoelectric constant d changes greatly. Similarly to this phenomenon, the composition range of 0.4 ≦ α ≦ 0.5 is a boundary between two types of crystal phases, and thus is a composition phase boundary MPB showing a specific phenomenon of the piezoelectric body, While the rate of temperature change of the constant d ₃₃ decreases to about 0, a large dynamic piezoelectric constant d ₃₃ is obtained.

The prepared sample was subjected to composition analysis with a fluorescent X-ray analyzer. As a result, the composition of the piezoelectric ceramic of each sample was the same ratio as the prepared raw material composition. This is because the ratio of Bi, Ti, Zr, Sr, Ba, Ca, Na, K, Li, Fe, Mn, Co and Cu among the detected elements is expressed by the composition formula Bi ₄ (Ti _1-γ Zr _{γ ) 3 O 12 · α [(} 1-β) M1 (Ti 1-γ Zr γ) O 3 · βM2M3O 3] ( provided that, M1 is _{Sr, Ba, Ca, (Bi} 0.5 Na 0.5), ( Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), at least one selected from Bi, Na, K and Li, and M3 selected from Fe and Nb is α by applying to at least one), to calculate the β and gamma, the components of the composition formula amounts and _MnO 2, from CoO and the ratio of the amount of CuO _{2 MnO} 2, CoO and CuO ₂ is of the formula How many parts by weight with respect to 100 weight of ingredients It was confirmed by calculating whether the hit.

Is a schematic diagram showing an apparatus for evaluating the dynamic piezoelectric constant d ₃₃ of the piezoelectric ceramic. It is a figure explaining the hysteresis of the generated charge. It is a perspective view which shows the pressure sensor which is one Embodiment of the piezoelectric element of this invention. It is a perspective view which shows the shock sensor which is one Embodiment of the piezoelectric element of this invention. Sample No. 1 (α = 0), No. 1 6 (α = 0.45) and no. 11 is an X-ray diffraction diagram of a piezoelectric ceramic having 11 (α = 01). FIG. It is the figure which expanded the A section of the X-ray-diffraction figure of FIG.

Explanation of symbols

l ... Base 2a, 2b ... Electrode 4 ... Polarization direction 5 ... Piezoelectric element

Claims (4)

When the composition formula is expressed as Bi ₄ (Ti _1-γ Zr _γ ) ₃ O ₁₂ · α [(1-β) M1 (Ti _1-γ Zr _γ ) O ₃ · βM2M3O ₃ ], 0.3 ≦ α ≦ 0.95, 0 ≦ β ≦ 0.5, 0.01 ≦ γ ≦ 0.3, and M1 is Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _{0. 5} Li _0.5 ) and (Bi _0.5 K _0.5 ), M2 is at least one selected from Bi, Na, K and Li, and M3 is Fe and At least one selected from Mn, Co and Cu is 0 in total in terms of oxide (MnO ₂ , CoO, CuO ₂ ) with respect to 100 parts by mass of the main component of the bismuth layered compound which is at least one selected from Nb. A piezoelectric ceramic characterized by containing 1-1.1 parts by mass. In the composition formula, Mn, Co and 100 parts by mass of the main component of the bismuth layered compound satisfying 0.4 ≦ α ≦ 0.7, 0 ≦ β ≦ 0.3, and 0.1 ≦ γ ≦ 0.2. _2. The piezoelectric ceramic according to claim 1, wherein at least one selected from Cu is contained in an amount of 0.1 to 0.5 parts by mass in terms of oxide (MnO ₂ , CoO, CuO ₂ ).   The piezoelectric ceramic according to claim 1, wherein 0.1 ≦ β.   A piezoelectric element comprising electrodes on a pair of opposing surfaces of a base body comprising the piezoelectric ceramic according to claim 1.

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