JP2010030814A - 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, having a high dynamic piezoelectric constant d<SB>33</SB>at a room temperature, having little variation of the dynamic piezoelectric constant d<SB>33</SB>to temperature and having high size accuracy and to provide a piezoelectric element. <P>SOLUTION: The piezoelectric ceramic is characterized by containing at least one kind selected from among Ln (lanthanoid), Y, Bi 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>3</SB>O<SB>12</SB>-α[(1-β)M1TiO<SB>3</SB>-βM2M3O<SB>3</SB>] (wherein, α and β are satisfied with 0.405≤α≤0.498 and 0≤β≤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, and is suitable for, for example, a resonator, an ultrasonic vibrator, an ultrasonic motor, or a piezoelectric sensor such as an acceleration sensor, a knocking sensor, and an AE sensor. The present invention relates to a piezoelectric ceramic and a piezoelectric element that are preferably used as a piezoelectric sensor utilizing a piezoelectric effect.

  Conventionally, products using piezoelectric ceramics include, for example, piezoelectric sensors, filters, piezoelectric resonators, ultrasonic vibrators, ultrasonic motors, and the like.

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

  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). Many piezoelectric ceramics mainly composed of bismuth layered compounds 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 sensor element to be used.
JP 2002-167276 A

However, the piezoelectric ceramic mainly composed of the bismuth layered compound described in Patent Document 1 is used for applications exposed to a high temperature of about 150 ° C., for example, as a piezoelectric element for a pressure sensor for directly detecting the pressure in a cylinder. In this case, although it has high heat resistance, the temperature change rate of the dynamic piezoelectric constant d ₃₃ that determines the pressure detection sensitivity is large, and in the temperature range of room temperature to 150 ° C., the pressure detection resolution is lowered and the sensitivity is deteriorated. There was a problem.

Here, 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. Conventionally, piezoelectric constant d ₃₃ is has been determined using the resonance impedance method, can not because the load is applied to the piezoelectric element is small, the evaluation of the dynamic characteristics at the time of applying the actual load is in this way. 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 .

As a specific measuring method, first, an offset load of 250 N was applied to the piezoelectric element, and a load of 50 N was applied in a triangular waveform in addition to the offset load. Then, the output charge Q with respect to the peak load 50N of the triangular wave applied to the piezoelectric element was evaluated 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 (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 without applying a tensile force to the piezoelectric element. The reason why the load change is set to 50 N is to cover the range necessary to detect the load change in the cylinder of the engine as an application example of the present invention.

  In addition, when incorporating such a piezoelectric element into a piezoelectric sensor, the dimensional accuracy of the piezoelectric element is important. As a method for increasing the dimensional accuracy, a method of processing after firing is conceivable, but the number of steps increases, and the piezoelectric element cracks due to processing, resulting in a low yield, pressure due to fine cracks remaining after processing, etc. It is preferable that the dimensional accuracy after firing is high so that the processing of the piezoelectric element may not be performed after firing, because the reliability of the piezoelectric element may be reduced, for example, when cracks are added.

Therefore, the present invention provides a piezoelectric ceramic and a piezoelectric element that are excellent in heat resistance, have a high dynamic piezoelectric constant d ₃₃ at room temperature, have a small change in the dynamic d ₃₃ constant with respect to temperature, and have high dimensional accuracy. For the purpose.

In the piezoelectric ceramic according to the present invention, when the composition formula is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498, 0 ≦ β ≦ 0. .3 and M1 is selected from Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ) 100 parts by mass of the main component of the bismuth layered compound, wherein M2 is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb. On the other hand, at least one selected from Ln (lanthanoid), Y, Bi and Cu is 0.1 to 1 in terms of oxide (Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ O ₃ , CuO ₂ ). Contains mass parts Than is.

  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, when the composition formula is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498, 0 ≦ β ≦ 0.3 with satisfying, M1 _{is, Sr, Ba, Ca, (} Bi 0.5 Na 0.5), (Bi 0.5 Li 0.5) and _{(Bi 0.5 K 0.5)} 100 masses of the main component of the bismuth layered compound in which M2 is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb And at least one selected from Ln (lanthanoid), Y, Bi, and Cu is 0.1 in terms of oxide (Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ O ₃ , CuO ₂ ) By containing ~ 1 part by mass Perovskite crystal structure in the bismuth layer compound, for a composition phase boundary MPB the tetragonal and orthorhombic crystals and are mixed, for dynamic piezoelectric constant d ₃₃ at room temperature, the 0.99 ° C. dynamic piezoelectric constant d ₃₃ The temperature change is within ± 5% and the temperature stability is excellent.

Furthermore, since a large dynamic piezoelectric constant d ₃₃ is obtained and has a high Curie point, even when left at a high temperature of 150 ° C., the dynamic piezoelectric constant d ₃₃ is hardly deteriorated and has excellent heat resistance. .

  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 polycrystalline body, it does not have the property of being easily broken on a specific surface like a single crystal, and chipping and the like are less likely to occur, resulting in fewer defects due to them and yield. Can be obtained.

In the piezoelectric ceramic of the present invention, when the composition formula based on the molar ratio is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498, 0 ≦ While satisfying β ≦ 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. ) A main component 100 of a bismuth layered compound, wherein M2 is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb. It contains at least one selected from Ln (lanthanoid), Y, Bi, and Cu in an amount of 0.1 to 1 part by mass in terms of oxide with respect to part by mass.

Here, the reason why the coefficient α is set in the above range will be described. In the above composition formula, the reason why the range of 0.405 ≦ α ≦ 0.498 is set is that when α is larger than 0.498, the temperature change of the dynamic piezoelectric constant d ₃₃ from 25 ° C. to −40 and 150 ° C. This is because the rate becomes larger than + 5%. Further, if α is smaller than 0.405, the rate of temperature change from 25 ° C. to −40 and 150 ° C. of the dynamic piezoelectric constant d ₃₃ is out of the range of ± 5%.

In the range of alpha is 0.405 ≦ α ≦ 0.498, the temperature change rate of the dynamic piezoelectric constant d ₃₃ together with taking a value greater than 15pC / N, to 0.99 ° C. from 25 ° C. dynamic piezoelectric constant d ₃₃ Behaves from-to +. FIG. 1 shows the result of analysis by X-ray diffraction of the change in crystal structure when α of a piezoelectric ceramic containing La as a lanthanoid is changed. FIG. 2 is an enlarged view of 2θ = 32 to 34 ° in FIG. When α = 0, the crystals are orthorhombic (a-axis length ≠ b-axis length), and when α = 1, they are tetragonal (a-axis length = b-axis length). . In the range of α = 0.405 to 0.498, tetragonal crystals and orthorhombic crystals are mixed, which is the composition phase boundary MPB. 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, since the composition range of 0.405 ≦ α ≦ 0.498 is a boundary between two types of crystal phases, it is a composition phase boundary MPB indicating a specific phenomenon of the piezoelectric body, and is a dynamic piezoelectric layer. While the rate of temperature change of the constant d ₃₃ decreases to about 0, a large dynamic piezoelectric constant d ₃₃ is obtained.

FIG. 3 shows a portion of 2θ = 32 to 34 ° as a result of analyzing the change in crystal structure by changing the α of the piezoelectric ceramic containing Cu by X-ray diffraction. This is the same result as the X-ray analysis of FIG. 2, and in the range of α = 0.405 to 0.498, tetragonal crystals and orthorhombic crystals are mixed, which is the composition phase boundary MPB. Such a tendency is the same also in the piezoelectric ceramic containing Bi deviating from the composition ratio of Y and the main component. When any element is contained, the composition range of 0.405 ≦ α ≦ 0.498 is dynamic. The rate of change in temperature of the piezoelectric constant d ₃₃ decreases to about 0, and a large dynamic piezoelectric constant d ₃₃ is obtained.

  Here, the firing temperature of the piezoelectric ceramic of the present application will be described. The optimum firing temperature of the piezoelectric ceramic of the present application varies depending on the elements contained and the ratio thereof, but is within a range of about 1050 to 1250 ° C. When firing at a temperature higher than the optimum firing temperature, the proportion of different phases that precipitate increases, resulting in lower piezoelectric properties, lower volume resistivity, making polarization treatment impossible, and sticking to the firing jig during firing. . Further, when firing at a temperature lower than the optimum firing temperature, the firing does not sufficiently shrink and the size becomes large or the piezoelectric characteristics are lowered.

Specifically, when the composition formula which is a piezoelectric ceramic within the scope of the present invention is represented by Bi ₄ Ti ₃ O ₁₂ · α [(1-β) Sr _0.5 Ba _0.5 TiO ₃ · βBiFeO ₃ ], α = 0.47, the sample in the embodiment of the piezoelectric ceramic a (described later containing 0.5 parts by mass of La lanthanoids in _La 2 _{O 3} in terms with respect to the main component of 100 parts by weight of a beta = 0.1 No. 7) is compared with a piezoelectric ceramic B (sample No. 51 in the examples described later) outside the scope of the present invention which has the same main component and does not contain Ln, Y, Bi and Cu as additives. Both piezoelectric ceramics have an optimum firing temperature of about 1150 ° C.

FIG. 4A shows the relationship between the firing temperature and the dynamic piezoelectric constant d ₃₃ of the piezoelectric ceramic when firing at a firing temperature of about 1150 ° C., and FIG. 4B shows the relationship between the firing temperature and the dimensions of the piezoelectric ceramic. Show. When the dynamic piezoelectric constant d ₃₃ is lower than the optimum firing temperature, the sintering proceeds as the temperature increases, and the dynamic piezoelectric constant d ₃₃ increases. When the optimum firing temperature is exceeded, the dynamic piezoelectric constant d ₃₃ gradually decreases, and when the firing temperature exceeds 1160 ° C., large voids are generated in the piezoelectric ceramic, and the dynamic piezoelectric constant d ₃₃ pressure further decreases. In the piezoelectric ceramic B that does not contain Ln, Y, Bi and Cu as additive components with respect to the main component, the dynamic piezoelectric constant d ₃₃ greatly changes with respect to the change in the firing temperature, and the dynamic piezoelectric when fired at the optimum firing temperature. temperature range is only about 20 ° C. to decrease the dynamic piezoelectric constant d ₃₃ is within 5% with respect to the constant d _33. On the other hand, in the piezoelectric ceramic A containing 0.5 parts by mass of La in terms of La ₂ O ₃ with respect to 100 parts by mass of the main component, the dynamic piezoelectric constant d ₃₃ hardly changes due to the change in the firing temperature. There is a temperature range of about 40 ° C. Further, the temperature range in which the decrease in the dynamic piezoelectric constant d ₃₃ within 5% of the dynamic piezoelectric constant d ₃₃ when firing at the optimum firing temperature is as wide as about 60 ° C.

  In the piezoelectric ceramic B, the temperature range in which the dimensional accuracy is within ± 1.5% of the fired piezoelectric ceramic having a firing temperature of 1150 ° C. is only about 15 ° C. In the piezoelectric ceramic A, the dependence of the dimensions on the firing temperature is very small in the temperature range of about 40 ° C. Further, the range in which the dimensional accuracy is within ± 1.5% is as wide as about 50 ° C.

By including La in this way, the firing temperature range in which stable characteristics can be obtained can be widened. Here, as a stable firing temperature range, a temperature range in which a decrease in the dynamic piezoelectric constant d ₃₃ is within 5% and a dimensional difference is within ± 1.5% with respect to a piezoelectric ceramic fired at an optimum firing temperature is considered. The dimensions do not vary greatly even when the firing temperature is higher than the optimum firing temperature, but the change is large when the firing temperature is lower than the optimum firing temperature. For this reason, the upper limit of the temperature is determined by a decrease in the dynamic piezoelectric constant d ₃₃ and the lower limit of the temperature tends to be determined by the size. In the above example, the stable firing temperature range of the piezoelectric ceramic A is 50 ° C. The stable firing temperature range is 15 ° C.

Ln, Y, Bi and Cu contained in 100 parts by mass in the main component which is a bismuth layered compound are the total amount in terms of oxide (Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ O ₃ , CuO ₂ ). And 0.1 to 1 part by mass. If the amount is less than 0.1 parts by mass, the stable firing temperature range is hardly improved. On the other hand, when the amount is more than 1 part by mass, the precipitation of different phases increases and the dynamic piezoelectric constant d ₃₃ decreases. A more preferred range is high improvement effect of stable firing temperature range, by sintering property is improved, a dynamic piezoelectric constant d ₃₃ becomes higher 0.5-0.8 parts by weight.

Specifically, Ln (lanthanoid) is at least one selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among lanthanoids, La and Nd are preferable in that the optimum firing temperature range is widened, and La is particularly preferable in that the dynamic piezoelectric constant d ₃₃ is increased.

Further, among Ln, Y, Bi and Cu, Ln and Y are preferable in terms of widening the stable firing temperature range, and Ln is particularly preferable. Further, Bi and Cu are preferable in that the dynamic piezoelectric constant d ₃₃ can be increased, and Bi is particularly preferable.

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 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

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 ≦ 0.3 is that when β is larger than 0.3, the dynamic piezoelectric constant d ₃₃ is lowered. M2M3O ₃ has the effect of extending the stable range of dimensions sintering temperature capable of obtaining (shrinkage) (stable firing temperature range). By setting 0.1 ≦ β ≦ 0.3, the stable firing temperature range can be widened by about 10 ° C. as compared to the case of β = 0 without significantly reducing the dynamic piezoelectric constant d ₃₃ . In that widen the stable firing temperature range, M2M3O ₃ is particularly preferably from BiFeO _3.

By selecting the composition ratio as described above, the dynamic piezoelectric constant d ₃₃ has a large dynamic piezoelectric constant d ₃₃ , high heat resistance, and the temperature change of the dynamic piezoelectric constant d ₃₃ from 25 ° C. to −40 and 150 ° C. A lead-free piezoelectric ceramic having a small bismuth layer structure can be obtained.

In the piezoelectric ceramic of the present invention, the composition formula of the main component is represented by Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ + βM2M3O ₃ ], and the main crystal phase is composed of a bismuth layered compound. This is basically a bismuth layered compound represented by Bi ₄ Ti ₃ O ₁₂ .alpha.M1TiO ₃ , or a part of M1 constituting the suspected perovskite layer of this bismuth layered compound is M2 and a part of Ti. The part is considered to have been replaced with M3. In other words, the piezoelectric ceramic according to the present invention includes an α site, a β site, and an oxygen in a general formula of a bismuth layered structure expressed by (Bi ₂ O ₂ ) ²⁺ (α _m−1 β _m O _{3m + 1} ) ^2−. The composition phase boundary MPB (Morphotoropic Phase Boundary) in which the tetragonal crystal generated when m = 4 and the orthorhombic crystal generated when m = 3 are mixed by adjusting the kind and amount of the constituent elements coordinated to the site. The bismuth layered structure in 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.

  Further, at least one selected from Ln, Y, Bi and Cu contained therein is solid-solved in the main crystal phase, and a part thereof includes at least one selected from Ln, Y, Bi and Cu. In some cases, crystals of the compound may be precipitated at the grain boundary, and as other crystal phases, there may be a pyrochlore phase, a perovskite phase, or a bismuth layered compound having a different structure.

In the piezoelectric ceramic according to the present invention, Zr or the like may be mixed from the ZrO ₂ ball at the time of pulverization.

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 , Ln ₂ O ₃ , Y ₂ O ₃ 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. Specifically, Ln (lanthanoid) is at least one selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

When these raw materials are expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498 and 0 ≦ β ≦ 0.3 are satisfied. , M1 is at least one selected from 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 at least one selected from Fe and Nb, with respect to 100 parts by mass of the main component of the bismuth layered compound, Ln (lanthanoid) ), At least one selected from Y, Bi and Cu was weighed so as to contain 0.1 to 1 part by mass in terms of oxide. The weighed and mixed powder is pulverized so that the average particle size distribution (D ₅₀ ) is in the range of 0.5 to 1 μm, the mixture is calcined at 800 to 1050 ° C., and a predetermined organic binder is added and wet mixed. 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 optimal as a piezoelectric ceramic for a pressure sensor as shown in FIG. 5, but other piezoelectric resonators, ultrasonic vibrators, ultrasonic motors and acceleration sensors, knocking sensors, AE sensors, etc. It can be used for piezoelectric sensors.

  FIG. 5 shows a piezoelectric element 5 according to an embodiment of the present invention. The piezoelectric element 5 is configured by forming electrodes 2 and 3 on a pair of opposed surfaces of a cylindrical substrate 1 made of the above-described piezoelectric ceramic. In FIG. 5, the electrodes 2 and 3 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. 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.

First, SrCO ₃ powder having a purity of 99.9%, BaCO ₃ powder, CaCO ₃ powder, Bi ₂ O ₃ powder, TiO ₂ powder, Na ₂ CO ₃ powder, K ₂ CO ₃ powder, Li ₂ CO ₃ powder as starting materials , Fe ₂ O ₃ powder and Nb ₂ O ₅ powder, M1, M2, M3 when the composition formula by molar ratio is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ] , Α, and β were weighed so that the elements and ratios shown in Tables 1 and 2 were obtained.

Ln ₂ O ₃ powder, Y ₂ O ₃ powder, Bi ₂ O ₃ powder and CuO ₂ powder are weighed to 100 parts by weight of the main component so as to be parts by weight shown in Table 1 and Table 2, and mixed. The mixture was placed in a 500 ml resin pot together with 99.9% pure zirconia balls and 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. Were also prepared even piezoelectric ceramic was subjected to firing by changing the firing peak temperature at intervals of 5 ° C. in the range from -50 to + 20 ° C. relative to the firing peak temperature dynamic piezoelectric constant d ₃₃ of the above is highest.

  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.

Thereafter, the dynamic piezoelectric constant d ₃₃ at room temperature (25 ° C.) was 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 by a triangular wave of 1 Hz. 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, compared with the most dynamic piezoelectric constant d ₃₃ of higher was the average size of the sample temperature, with a decrease of the dynamic piezoelectric constant d ₃₃ of the average of the sample to change the peak temperature of firing is within 5% Tables 1 and 2 show the temperature range in which the average dimension of the samples is within ± 1.5% as the stable firing temperature range. When this temperature range is wide, it is possible to produce a piezoelectric ceramic having stable dimensional characteristics with good dimensional accuracy even when the firing temperature varies during manufacturing. The dimensions were evaluated by the diameter of a cylindrical piezoelectric ceramic.

As is apparent from Tables 1 and 2, when the composition formula, which is a piezoelectric ceramic within the scope of the present invention, is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498 and 0 ≦ β ≦ 0.3 are satisfied, 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 selected from Fe and Nb At least one selected from Ln (lanthanoid), Y, Bi, and Cu is an oxide (Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ ) with respect to 100 parts by mass of the main component of at least one bismuth layered compound. O _3, CuO ₂₎ conversion Samples containing 0.1 parts by weight of a total of No. 5 to 8, 12 to 17, 19 to 21, 23 to 25, 27 to 29, 31 to 33, 35 to 37, 39 to 44, 46, 47, 49, 50 and 53 to 56 are dynamic piezoelectric constants d. ₃₃ is as high as 15.3 pC / N or more, and the rate of change of the dynamic piezoelectric constant d ₃₃ at −40 ° C. and 150 ° C. with respect to the dynamic piezoelectric constant d _{33 at} 25 ° C. is within ± 0.48%. The temperature dependency was low, and the stable firing temperature range was 30 ° C. or higher.

On the other hand, when expressed by the composition formula, 0.405 ≦ α ≦ 0.498 and 0 ≦ β ≦ 0.3 are satisfied, 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 And at least one selected from Ln (lanthanoid), Y, Bi and Cu with respect to 100 parts by mass of the main component of the bismuth layered compound in which M3 is at least one selected from Fe and Nb Sample No. 1 outside the scope of the present invention, which does not satisfy any of the conditions for containing 0.1 to 1 part by mass in total. 1 to 4, 9 to 11, 18, 22, 26, 30, 34, 38, 45, 48, 51, 52 and 57, 13.7 pC / N or less, or the dynamic piezoelectric constant d _{33 at} 25 ° C. The rate of change of the dynamic piezoelectric constant d ₃₃ at −40 and 150 ° C. became ± 5.1% or more, or the stable firing temperature range narrowed to within 20 ° C.

FIG. 1 (α = 0), No. 1 7 (α = 0.47) and no. 11 is an X-ray diffraction diagram of 11 (α = 1). It can be seen from the X-ray diffraction pattern that the bismuth layered compound is the main crystal phase. The same applies to other piezoelectric ceramics within the scope of the present invention. Further, since the bismuth layered compound is recognized as the main crystal phase from the X-ray diffraction diagram, the perovskite compound of M2M3O ₃ was incorporated into the susceptible perovskite layer of the bismuth layered compound and became a part of the bismuth layered compound. Conceivable.

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, Sr, Ba, Ca, Na, Li, K, Nb, Fe, Ln, Y, and Cu among the detected elements is expressed by the composition formula Bi ₄ Ti ₃ O ₁₂ · α [ (1-β) M1TiO ₃ + βM2M3O ₃ ] (where M1 is Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _{0). .5} ) is applied to at least one selected from M), M2 is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb) to calculate α and β, From the ratio of the amount of the component of the composition formula and the amount of Ln, Y, Bi, and Cu, how many parts by weight of Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ O _3, and CuO ₂ is 100 parts by weight of the component of the composition formula To calculate and check It was.

It is an X-ray diffraction diagram of the piezoelectric ceramic (sample No. 7, α = 0.47) of the present invention and other piezoelectric ceramics (sample Nos. 1 and 11, α = 0 and 1). It is the figure which expanded the X section of the X-ray diffraction diagram of FIG. It is an X-ray diffraction pattern of the piezoelectric ceramic (sample No. 31, α = 0.47) of the present invention and other piezoelectric ceramics (α = 0 and 1). (A) is a diagram showing the relationship between the firing temperature and the dynamic piezoelectric constant d ₃₃ of the piezoelectric ceramic A (Sample No.7) to other piezoelectric ceramic B (Sample No.51) of the present invention. (B) It is a figure which shows the relationship between the calcination temperature and dimension of a same-pressure ceramic. It is a pressure sensor which is one embodiment of the piezoelectric element of the present invention. It is an explanatory view for explaining an evaluation device for dynamic piezoelectric constant d ₃₃ used in the present invention.

Explanation of symbols

l ... Base 2, 3 ... Electrode 4 ... Polarization direction 5 ... Piezoelectric element

Claims (2)

When the composition formula is expressed as Bi ₄ Ti ₃ O ₁₂ · α [(1-β) M1TiO ₃ · βM2M3O ₃ ], 0.405 ≦ α ≦ 0.498 and 0 ≦ β ≦ 0.3 are satisfied, M1 is at least one selected from Sr, Ba, Ca, (Bi _0.5 Na _0.5 ), (Bi _0.5 Li _0.5 ) and (Bi _0.5 K _0.5 ), Mn is at least one selected from Bi, Na, K and Li, and M3 is at least one selected from Fe and Nb, Ln (lanthanoid) with respect to 100 parts by mass of the main component of the bismuth layered compound , Y, Bi and Cu at least one selected from 0.1 to 1 parts by mass in terms of oxide (Ln ₂ O ₃ , Y ₂ O ₃ , Bi ₂ O ₃ , CuO ₂ ) Piezoelectric ceramic.   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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