JP5898032B2 - Piezoelectric ceramic and piezoelectric element using the same - Google Patents

Description

  The present invention relates to a piezoelectric ceramic, for example, positioning, optical path length control of an optical device, flow rate control valve, pump, ultrasonic motor, engine fuel injection device, automobile brake device, ink jet head of an ink jet printer, and the like. The present invention relates to a piezoelectric ceramic and a piezoelectric element which are preferably used for an actuator used.

  Examples of products using piezoelectric ceramics include filters, positioning, optical path length control of optical devices, flow control valves, and ultrasonic motors. In particular, the piezoelectric actuator can precisely control the displacement on the order of submicron, and in addition, the electro-mechanical conversion efficiency is high, so the response speed is fast and a large generation force can be obtained even with low power consumption. Therefore, it is also used for inkjet printer heads, diesel engine injectors, and the like.

Conventionally, PZT (lead zirconate titanate) -based materials and PT (lead titanate) -based materials having high piezoelectricity have been used as actuators. However, since PZT-based materials and PT-based materials contain lead in a proportion of about 60% by mass, the elution of lead due to acid rain has been pointed out as a risk of environmental pollution. Therefore, high expectations are placed on piezoelectric materials that do not contain lead as a main component. In particular, lead-free alkali niobate-based piezoelectric materials in which an alkali metal is arranged at the A site of the perovskite structure (general formula ABO ₃ ) and niobium is arranged at the B site are actively researched and developed. ing.

However, since a piezoelectric ceramic using only an alkali niobate has a low piezoelectric constant, for example, in Patent Document 1, {Li _x (K _1-y Na _y ) _1-x } (Nb _1-zw Ta _z Sb _w ) O ₃ , where 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4, 0 ≦ w ≦ 0.2, and x + z + w> 0 0.0001 to 0.15 mol of any one or more additive elements selected from metal elements belonging to group 2 to 15 in the periodic table, metalloid elements, transition metal elements, noble metal elements, and alkaline earth metal elements There has been proposed a crystallographically-oriented ceramic, which is a polycrystalline ceramic containing, characterized in that specific crystal planes of crystal grains constituting the polycrystalline are oriented.

  By adopting such a composition, the phase transition point between the orthorhombic crystal and the tetragonal crystal, both of which are ferroelectric phases, is in the vicinity of room temperature, the piezoelectric constant in the vicinity of room temperature is increased, and a specific crystal of the crystal grain By orienting the plane, the piezoelectric constant is further increased.

JP 2006-028001 A

  However, the crystal-oriented ceramic described in Patent Document 1 has a problem that the piezoelectric constant increases rapidly near the room temperature where the phase transition point is present, and the temperature dependence of the piezoelectric characteristics also increases.

The present invention has been made in view of such circumstances, and uses a potassium niobate / sodium niobate-based piezoelectric material that does not contain lead. Even if the piezoelectric constant is high, the temperature dependence of the piezoelectric characteristics is small and a wide temperature range. An object is to provide a piezoelectric ceramic having high and stable piezoelectric characteristics over a range.

The piezoelectric ceramic of the present invention has a composition formula (1-x) {(K _1-a Na _a ) _{1 -b} Li _b } _c (Nb _1- de Ta _d Sb _e ) O ₃ + xBi _α (A1 _{1- The} component represented by _β A2 _β ) O ₃ and Mn are contained in an amount of 0.01 to 0.50 parts by mass in terms of MnO _{2 with} respect to 100 parts by mass of the component of the composition formula. And x, a, b, c, d, e, α, β in the composition formula are
0.0010 ≦ x ≦ 0.0050,
0.50 ≦ a ≦ 0.54,
0.02 ≦ b ≦ 0.06,
1.000 ≦ c ≦ 1.005,
0.04 ≦ d ≦ 0.10,
0 ≦ e ≦ 0.10,
2/3 ≦ α ≦ 1,
β = 1/2 ,
A1 is at least one element selected from the group consisting of Mg, Cu and Zn, and A2 is at least one selected from the group consisting of Sn, Ti, Zr, Hf, Ce and Ge. It is characterized by being.

  The piezoelectric element according to the present invention is characterized in that the above-described piezoelectric ceramic has a facing surface, and a pair of electrodes disposed on the facing surface so as to face each other.

  According to the present invention, a lead-free potassium niobate / sodium niobate-based piezoelectric material is used, and even if the piezoelectric constant is high, the temperature dependence of the piezoelectric characteristics is small, and the piezoelectric characteristics have high and stable piezoelectric characteristics over a wide temperature range. Porcelain and piezoelectric elements can be provided.

(A) is a schematic perspective view of the pressure sensor element which is an example of embodiment of the piezoelectric element of this invention, (b) is a schematic longitudinal cross-sectional view of the actuator which is an example of embodiment of the piezoelectric element of this invention It is. Sample No. 4 is a diagram showing an X-ray diffraction (XRD) pattern of No. 4; FIG. Sample No. 1 and sample no. 4 is a graph showing temperature characteristics of a dielectric constant of 4. FIG.

The piezoelectric ceramic of the present invention is mainly composed of potassium niobate and sodium that do not contain lead, and Mn is 0.01 to 0.50 parts by mass in terms of MnO ₂ with respect to 100 parts by mass of the component represented by Formula 1. contains.

Here, x, a, b, c, d, e, α, β are respectively
0.0010 ≦ x ≦ 0.0050,
0.50 ≦ a ≦ 0.54,
0.02 ≦ b ≦ 0.06,
1.000 ≦ c ≦ 1.005,
0.04 ≦ d ≦ 0.10,
0 ≦ e ≦ 0.10,
2/3 ≦ α ≦ 1,
1/3 ≦ β ≦ 2/3,
A1 is at least one element group consisting of Mg, Cu and Zn, and A2 is an element group consisting of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn and Ce. By using at least one of them, even if the piezoelectric constant is large, the temperature dependence of the piezoelectric characteristics is small, and high and stable piezoelectric characteristics can be obtained over a wide temperature range.

  In the formula 1, potassium niobate / sodium niobate having a composition represented by the following formula 2 is a main component of the piezoelectric ceramic and has a perovskite structure.

In Equation 2, the range of a, b, c, d, e is 0.50 ≦ a ≦ 0.54,
0.02 ≦ b ≦ 0.06,
1.000 ≦ c ≦ 1.005,
0.04 ≦ d ≦ 0.10,
0 ≦ e ≦ 0.10,
As a result, the piezoelectric constant of the piezoelectric ceramic increases. This is a composition range that becomes a so-called MPB (Morphotoropic Phase Boundary) region including a boundary where the crystal structure changes depending on the composition.

  That is, in Equation 2, by setting a to a range of 0.50 ≦ a ≦ 0.54 and substituting a part of K with Na, the piezoelectric constant can be increased.

  Further, b is set to 0.02 or more, and by introducing Li into the A site, the sinterability of the piezoelectric ceramic can be improved, and by setting b to a range of 0.02 ≦ b ≦ 0.06, The piezoelectric constant can be increased.

  The reason why d is in the range of 0.04 ≦ d ≦ 0.10 is that the piezoelectric constant can be increased by replacing part of Nb with Ta. Note that when d exceeds 0.10, the piezoelectric constant decreases and the Curie temperature may decrease.

  The reason why e is in the range of 0 ≦ e ≦ 0.10 is that the sinterability can be improved by replacing part of Nb with Sb as necessary. In addition, when e exceeds 0.10, there exists a possibility that sinterability may fall.

  c is in the range of 1.000 ≦ c ≦ 1.005. This is because if the A site atom of the perovskite structure is excessively contained in excess of 1.005 with respect to the B site atom, there is a concern that the piezoelectric characteristics are deteriorated.

However, although the above-mentioned potassium niobate / sodium is a composition that becomes the MPB region,
A piezoelectric ceramic having such a composition exhibits high piezoelectric characteristics, but the temperature dependence of the piezoelectric characteristics is large. In addition, in order to obtain a dense piezoelectric ceramic having this composition, it is necessary to perform firing at a high temperature, and the range of firing temperatures at which a piezoelectric ceramic exhibiting high piezoelectric characteristics can be obtained is narrow and the high piezoelectric characteristics can be reproduced reproducibly. It was difficult to obtain a piezoelectric ceramic.

  The present inventors have introduced a piezoelectric complex having a high piezoelectric constant over a wide temperature range by introducing Bi composite oxide represented by the following formula 3 and Mn into such potassium niobate and sodium. It was found that the temperature dependence of the piezoelectric characteristics can be reduced.

  The Bi composite oxide represented by Formula 3 has a composite perovskite structure, and Bi has 6s2 lone electron pairs, and thus has a large distortion in the crystal structure. By introducing a predetermined amount of this Bi composite oxide into potassium / sodium niobate represented by Formula 2, strain is introduced into the crystal structure of potassium / sodium niobate to increase the polarization, and the piezoelectric characteristics are improved. At the same time, the temperature dependence of the piezoelectric characteristics can be reduced.

  In addition, since the compound containing Bi produces | generates a liquid phase at comparatively low temperature, the effect that the baking temperature of a piezoelectric ceramic falls by introducing Bi complex oxide is also acquired.

  Here, α is in the range of 2/3 ≦ α ≦ 1. By setting α within such a range, Bi composite oxide can be taken into potassium and sodium niobate without excess or deficiency. If α is smaller than 2/3, the piezoelectric characteristics may be deteriorated. If α is larger than 1, excessive Bi may remain at the grain boundaries, and the insulation of the piezoelectric ceramic may be deteriorated. .

  A1 is at least one element selected from the group consisting of Mg, Cu and Zn, and A2 is at least one selected from the group consisting of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn and Ce. One type. These have an ionic radius comparable to that of Nb in a six-coordinate state with oxygen.

  β is in the range of 1/3 ≦ β ≦ 2/3. By setting β in such a range, the ratio of A1 and A2 can be within the range of the stoichiometric ratio. If the ratio between A1 and A2 deviates significantly from the stoichiometric ratio, oxygen vacancies are formed, and the piezoelectric characteristics may be deteriorated.

  When A2 is an element that becomes a pentavalent ion, that is, at least one of Nb, Ta, and Sb, the stoichiometric ratio of A1 and A2 is set by setting α + β to 4/3. It is preferable to be within the range of In addition, when A2 is an element that becomes a tetravalent ion, that is, at least one of Ti, Zr, Hf, Ge, Sn, and Ce, A1 and A2 are reduced by reducing β to 1/2. It can be within the range of the stoichiometric ratio, and is preferable.

  Thus, by introducing the complex perovskite structure of the Bi composite oxide represented by Formula 3 into the perovskite structure of potassium niobate and sodium represented by Formula 2, the piezoelectric constant is increased and the piezoelectric characteristics are increased. The temperature dependence can be reduced.

The ratio of Bi composite oxide to potassium niobate / sodium niobate is represented by x in Formula 1, and x is 0.0010 ≦ x ≦ 0.0050. By setting x in such a range, an appropriate strain is introduced into the perovskite structure of potassium and sodium niobate and the piezoelectric constant can be increased. If x is smaller than 0.0010, a desired effect cannot be obtained. If x is larger than 0.0050, the introduced strain becomes too large and the piezoelectric characteristics are deteriorated.

Furthermore, the piezoelectric ceramic of the present invention contains 0.01 to 0.50 parts by mass of Mn in terms of MnO _{2 with} respect to 100 parts by mass of the component of Formula 1. As a result, the piezoelectric ceramic can be made denser and the piezoelectric constant can be further increased.

  In the piezoelectric ceramic according to the present invention, 99% by mass or more of the composition is occupied by the component of Formula 1 and the Mn component, and the other impurity elements are less than 0.5% by mass in terms of oxides, more preferably 0%. Less than 2% by mass, more preferably less than 0.1% by mass. Examples of impurity elements include those caused by the piezoelectric ceramic manufacturing process, such as Fe, Ni, Co, Cr, and Al. However, if the total amount is less than 0.5% by mass in terms of oxides, no problem. The composition of the piezoelectric ceramic and the content of impurity elements can be confirmed by elemental analysis such as fluorescent X-ray analysis and ICP emission spectroscopic analysis.

An example of the manufacturing method of the piezoelectric ceramic according to the present invention will be described. In order to produce the piezoelectric ceramic of the present invention, as raw materials, carbonates such as Na ₂ CO ₃ , K ₂ CO ₃ , Li ₂ CO ₃ and MgCO ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Sb ₂ O are used. ₃ , Bi ₂ O ₃ , ZnO, CuO, TiO ₂ , SnO ₂ , ZrO ₂ , HfO ₂ , Ce ₂ O ₃ , GeO ₂ and MnO ₂ may be used. The raw materials are not limited to these, and metal salts such as nitrates that generate oxides by firing may be used.

In the above-mentioned formula 1, A1 is at least one of Mg, Cu, and Zn, and A2 is at least one of Nb, Ta, Sb, Ti, Zr, Hf, Ge, Sn, and Ce. And using the above raw materials, x, a, b, c, d, e, α, β in Formula 1 are
0.0010 ≦ x ≦ 0.0050,
0.50 ≦ a ≦ 0.54,
0.02 ≦ b ≦ 0.06,
1.000 ≦ c ≦ 1.005,
0.04 ≦ d ≦ 0.10,
0 ≦ e ≦ 0.10,
2/3 ≦ α ≦ 1,
1/3 ≦ β ≦ 2/3,
And Mn is weighed so as to be 0.01 to 0.5 parts by mass in terms of MnO ₂ with respect to 100 parts by mass of the component of formula 1. The weighed raw materials are mixed to form a mixture, and the mixture is pulverized so that the average particle size (D50) in the particle size distribution is in the range of 0.3 to 1.0 μm. This mixture is calcined and synthesized at 850 to 1000 ° C. to obtain a composite. The obtained composite is pulverized and the average particle size (D50) in the particle size distribution is adjusted to a range of 0.3 to 1 μm. Thereafter, a predetermined binder is added and wet-mixed to obtain a granulated powder.

  The obtained granulated powder is molded into a predetermined shape by a known molding method such as press molding or tape molding, and fired in an oxidizing atmosphere such as the atmosphere for 2 to 5 hours at a temperature range of 1000 to 1150 ° C. The piezoelectric ceramic of the present invention is obtained.

The piezoelectric ceramic of the present invention may be composed of a single phase or a complex in which two or more kinds of particles having different compositions within the scope of the present invention are complexed. For the composite, for example, two or more kinds of composites having different compositions may be synthesized, and these two or more kinds of composites may be pulverized and mixed to produce a piezoelectric ceramic. Whether the piezoelectric ceramic is composed of a single phase or a composite is determined by, for example, analyzing the composition of each crystal particle constituting the piezoelectric ceramic or analyzing the X-ray diffraction pattern of the piezoelectric ceramic. it can.

  Such a piezoelectric ceramic is processed into a shape having an opposing surface as necessary, and a pair of electrodes are arranged on the opposing surface so as to face each other, whereby the piezoelectric element of the present invention is obtained.

  FIG. 1A is a schematic perspective view of a pressure sensor element that is an example of an embodiment of a piezoelectric element of the present invention. This pressure sensor includes a pair of electrodes 2 and 3 arranged to face each other on a pair of opposing main surfaces of a piezoelectric substrate 1 made of a piezoelectric ceramic having the above-described composition. Polarization is performed in a direction perpendicular to the main surface. In such a pressure sensor, electric charges are generated on the main surfaces due to the pressure applied between the main surfaces. Therefore, the pressure applied between the main surfaces can be measured by measuring the electric charges.

  FIG. 1B is a schematic longitudinal sectional view of an actuator which is an example of an embodiment of the piezoelectric element of the present invention. In this actuator, an electrode 12 is disposed on one main surface of a piezoelectric substrate 11 made of a piezoelectric ceramic having the above-described composition, and an electrode 13 is disposed on the other main surface. The polarization direction is the thickness direction of the piezoelectric substrate 1.

  In such an actuator, the piezoelectric substrate 11 is produced by polarization in the thickness direction of the piezoelectric ceramic produced as described above, and the electrodes 12 and 13 are arranged and adhered to the diaphragm 14 or the electrodes are attached to the piezoelectric ceramic. 12 and 13 are disposed and bonded to the diaphragm 14, and then polarized in the thickness direction of the piezoelectric ceramic. Such an actuator acts as an actuator by applying a voltage between the electrode 12 and the electrode 13 so that the piezoelectric substrate 11 contracts in a plane direction perpendicular to the thickness thereof and bends the diaphragm.

Hereinafter, the piezoelectric ceramic of the present invention will be described in detail based on examples. First, as a starting material, Na ₂ CO ₃ powder with a purity of 99.9%, K ₂ CO ₃ powder, Li ₂ CO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, Sb ₂ O ₃ powder, Bi ₂ O ₃ powder, MgCO ₃ powder, ZnO powder, CuO powder, TiO ₂ powder, SnO ₂ powder, ZrO ₂ powder, HfO ₂ powder, Ce ₂ O ₃ powder, GeO ₂ powder and MnO ₂ powder were prepared.

These powders are weighed so that x, a, b, c, d, e, α, and β in Formula 1 are the amounts shown in Table 1 and Table 2, and further, with respect to 100 parts by mass of the component of Formula 1 Then, Mn was weighed so as to have a ratio shown in Table 1 in terms of MnO ₂ .

The weighed raw material powder was put into a polypot together with ZrO ₂ balls having a purity of 99.9% and isopropyl alcohol (IPA), and mixed for 16 hours in a rotary mill. This mixture is taken out from the polypot and dried, followed by calcination and synthesis at a temperature of 900 to 1000 ° C. in the atmosphere for 3 hours, and the resultant composite is pulverized again in the same manner as described above to synthesize. A powder was obtained. Thereafter, polyvinyl alcohol (PVA) as a binder was mixed with the synthetic powder to produce a granulated powder.

  Next, the obtained granulated powder was molded into a disk shape having a diameter of 16 mm and a thickness of 1.5 mm at a pressure of 200 MPa. The compact was fired at 1000 to 1150 ° C. for 3 hours in the air to obtain a piezoelectric ceramic.

  The composition of the obtained piezoelectric ceramic was quantitatively analyzed by ICP emission spectroscopic analysis and confirmed to be the same as the composition of the raw material.

  Moreover, as a result of performing X-ray diffraction (XRD) measurement of the obtained porcelain and identifying a diffraction pattern, all the samples were mainly composed of perovskite crystals. As an example, sample no. The X-ray diffraction (XRD) pattern of 4 is shown in FIG.

  The piezoelectric characteristics of the obtained piezoelectric ceramic were evaluated as follows. After the thickness of the piezoelectric ceramic is 1 mm by polishing, Ag electrodes are formed on both main surfaces (upper and lower surfaces of the disk) of the piezoelectric ceramic, and polarization treatment is performed in the thickness direction of the disk-shaped piezoelectric ceramic. A piezoelectric element was produced at a temperature of 0 ° C.

The piezoelectric element produced was measured piezoelectric constant d ₃₃ with d ₃₃ meter. Further, while changing the temperature of the piezoelectric element in the thermostatic chamber, the temperature characteristic of the capacitance of the piezoelectric element was measured using an impedance analyzer, and the measured value was converted into a dielectric constant. In addition, the measurement of these piezoelectric characteristics was performed according to the Japan Electronic Materials Industry Association standard EMAS. Table 2 shows the piezoelectric constant d ₃₃ and the dielectric constant change rate Δε / εr of each sample. Sample No. FIG. 3 shows the temperature characteristics of dielectric constants 1 and 4 based on the value of the dielectric constant ε _r at 25 ° C.

The change rate Δε / ε _r of the dielectric constant is Δε which is the difference between the maximum value ε _max and the minimum value ε _min of the dielectric constant in the temperature range of −20 ° C. to + 150 ° C., and the dielectric constant ε _{r at} 25 ° C. Based on the value of.

Sample No. 18 , 19 , 26 to _{31, 33} to 35 , _{39 and} 40 are excellent in that the piezoelectric constant d ₃₃ is larger than 200, and the change rate Δε / ε _r of dielectric constant at −20 ° C. to + 150 ° C. is less than 50%. The piezoelectric characteristics were also exhibited. On the other hand, Sample No. which is outside the scope of the present invention. No. 1 had a piezoelectric constant d ₃₃ as small as 190 and Δε / ε _r as large as 81%, which was inferior in performance. Sample No. Reference numerals 2 to 17, 20 to 25, 32, and 36 to 38 are reference examples.

1, 11: Piezoelectric substrate (piezoelectric ceramic)
2, 3, 12, 13: electrode 14: vibrator P: direction of polarization

Claims (2)

Compositional formula (1-x) {(K _1-a Na _a ) _1-b Li _b } _c (Nb _1- de Ta _d Sb _e ) O ₃ + xBi _α (A1 _1−β A2 _β ) O ₃ The component represented, and Mn,
While the content of Mn is 0.01 to 0.50 parts by mass in terms of MnO _{2 with} respect to 100 parts by mass of the component of the composition formula,
X, a, b, c, d, e, α, β in the composition formula are respectively
0.0010 ≦ x ≦ 0.0050,
0.50 ≦ a ≦ 0.54,
0.02 ≦ b ≦ 0.06,
1.000 ≦ c ≦ 1.005,
0.04 ≦ d ≦ 0.10,
0 ≦ e ≦ 0.10,
2/3 ≦ α ≦ 1,
β = 1/2 ,
Range of
A1 is at least one selected from the group consisting of Mg, Cu and Zn,
A piezoelectric ceramic, wherein A2 is at least one of an element group consisting of Sn, Ti, Zr, Hf, Ce, and Ge . 2. The piezoelectric element according to claim 1 , wherein the piezoelectric ceramic has a facing surface, and a pair of electrodes arranged on the facing surface so as to face each other.

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