JP2015096455A - Piezoelectric ceramic composition, piezoelectric element, sensor for internal combustion engine and manufacturing method for piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition capable of achieving high Curie temperature, low pyroelectricity, high temperature stability for example even when used under environment changing from low temperature to high temperature, a piezoelectric element using the piezoelectric ceramic composition, a sensor for an internal combustion engine containing the piezoelectric element and a manufacturing method for the piezoelectric ceramic composition.SOLUTION: There is provided for example a piezoelectric element containing a piezoelectric ceramic consisting of a piezoelectric ceramic composition having a lamellar structure oxide containing Ti and a bismuth laminar structure compound, for example the lamellar structure oxide is ATiBO, where element A is an alkali metal, element B is at least one kind of Nb and Ta and x is any, and 0.030≤a≤0.042, 0.330≤b≤0.370 and 0.580≤c≤0.640 when for example the bismuth laminar structure compound is aNaO-bBiO-cTiO.

Description

  The present invention relates to a piezoelectric ceramic composition having a piezoelectric characteristic whose electrical characteristics change when pressure is applied, a piezoelectric element using the piezoelectric ceramic composition, a sensor for an internal combustion engine using the piezoelectric element, and a piezoelectric ceramic. The present invention relates to a method for producing a composition.

  Conventionally, a strain gauge that measures the amount of deformation caused by a mechanical load or a piezoelectric sensor that generates electric charges by applying a mechanical load to a piezoelectric element has been used for pressure measurement. In general, the former is suitable for static measurement in which the force changes slowly, and the latter is suitable for measurement in a state where the force changes rapidly.

Among these, the piezoelectric sensor has a characteristic that measurement conditions are restricted by a Curie point temperature (Curie temperature: Tc), which is a critical temperature at which the piezoelectric characteristics of the piezoelectric element itself disappear.
The Curie temperatures of commonly used piezoelectric elements are 320 ° C. for lead zirconate titanate (PZT), 490 ° C. for lead titanate (PT), and 550 ° C. for quartz.

On the other hand, lithium niobate (LiNbO ₃ ) and langasite (La ₃ Ga ₅ SiO ₁₄ ) have characteristics such as a Curie temperature of 1200 ° C. and no Curie point. For this reason, these crystals can be used at very high temperatures, but since these are single crystals, the growth and processing of the crystals are complicated, and the device price is expensive.

  As this type of technology, a piezoelectric element composed of a piezoelectric ceramic composition made of a bismuth layered structure compound is disclosed (see Patent Document 1). Also, a piezoelectric ceramic composition in which a lamellar structure oxide is contained in a niobium / alkaline tantalate perovskite oxide is disclosed (see Patent Document 2).

  In recent years, a piezoelectric element is incorporated in an automobile engine or the like, and the pressure applied to the piezoelectric element is sensed by using a positive piezoelectric effect to be used for engine combustion control, vehicle attitude control, or the like. .

  In particular, as an internal combustion engine sensor used for engine control, a pressure sensor for detecting the pressure (combustion pressure) in the engine cylinder or a knocking sensor for detecting engine knocking for the purpose of purifying exhaust gas and improving fuel consumption. Is known (see Patent Document 3).

WO2010 / 001542 Publication WO2011 / 093021 Publication JP 2009-84067 A

  However, since the piezoelectric element used in the above-described sensor for an internal combustion engine is mounted on the engine, it is desired that the piezoelectric element has a characteristic that functions sufficiently even at a high temperature, that is, has a high Curie temperature.

  In addition, in order to improve fuel efficiency, it is necessary to precisely measure the pressure in the engine cylinder that changes from low temperature to high temperature, and fine engine control is required. That is, it is desired that the pyroelectricity (characteristic of increasing or decreasing the charge on the surface in accordance with a change in temperature) is low and the temperature stability is high.

  The present invention has been made in order to solve the above-described problems, and its purpose is, for example, even when used in an environment where the temperature changes from low to high, high Curie temperature, low pyroelectricity, and high temperature stability. It is an object to provide a piezoelectric ceramic composition capable of realizing the characteristics, a piezoelectric element using the piezoelectric ceramic composition, a sensor for an internal combustion engine including the piezoelectric element, and a method for manufacturing the piezoelectric ceramic composition.

(1) The present invention is characterized by having a lamellar structure oxide containing Ti and a bismuth layered structure compound as a first aspect (piezoelectric ceramic composition).
Since the piezoelectric ceramic composition of the first aspect has a lamellar structure oxide containing Ti and a bismuth layered structure compound, the Curie temperature is high (for example, 500 ° C. or more) and the pyroelectricity is low (that is, temperature Even if the voltage increases, the electric charge is small, and the piezoelectric property is excellent (that is, the piezoelectric constant is high and sufficient electric charge corresponding to the pressure can be obtained). Therefore, even when the temperature changes (especially when the temperature rises), a characteristic that sufficiently and accurately responds to the change in pressure can be obtained. Property).

  That is, in the piezoelectric ceramic composition according to the first aspect, even when the temperature changes, the change in the piezoelectric constant is small. Therefore, when applied to a piezoelectric element, for example, a stable element output can be obtained. For example, the rate of change of the piezoelectric constant d33 can be 2% or less.

In addition, the piezoelectric ceramic composition of the first aspect is excellent in heat resistance and can ensure high piezoelectric performance even at high temperatures, so that it can be used at high temperatures such as in an engine cylinder.
Furthermore, since the piezoelectric ceramic composition of the first aspect is polycrystalline, there is an advantage that a single crystal is less expensive than a material.

In addition, since the lead-free piezoelectric ceramic composition which does not contain lead is realizable by the piezoelectric ceramic composition of this 1st aspect, there exists an effect that there is no possibility of polluting an environment with lead.
(2) In the present invention, as a second aspect, the lamellar structure oxide is A _1-x Ti _1-x B _{1 + x} O ₅ (the element A is an alkali metal, the element B is at least one of Nb and Ta, x is arbitrary).

  The second embodiment exemplifies preferred lamellar structure oxides (including Ti). A piezoelectric ceramic composition containing a lamellar structure oxide having this composition has an advantage of high Curie temperature, excellent piezoelectric characteristics, and high temperature stability as described above.

(3) As a third aspect, the present invention is characterized in that the x satisfies 0 ≦ x ≦ 0.15.
The third aspect exemplifies a preferable range of x. The lamellar structure oxide having this configuration has an advantage of high crystal stability.

(4) In the present invention, as a fourth aspect, when the bismuth layered structure compound is aNa ₂ O—bBi ₂ O ₃ —cTiO ₂ , 0.030 ≦ a ≦ 0.042, 0.330 ≦ b ≦ 0.370 and 0.580 ≦ c ≦ 0.640.

  The fourth embodiment exemplifies a preferable bismuth layered structure compound. The bismuth layered structure compound having this composition is excellent in piezoelectric characteristics and has a high Curie temperature (for example, 500 ° C. or higher), so that even when a piezoelectric ceramic composition is used at a high temperature, it is suitable for pressure. Characteristics are obtained.

(5) As a fifth aspect, the present invention is characterized in that a Na _0.5 Bi _4.5 Ti ₄ O ₁₅ type crystal is a main crystal.
The fifth aspect exemplifies a more preferred bismuth layered structure compound. Since this crystal is excellent in piezoelectric characteristics and has a high Curie temperature (for example, 500 ° C.), a piezoelectric ceramic composition having this crystal as a main crystal can obtain suitable piezoelectric characteristics corresponding to pressure.

Hereinafter, this Na _0.5 Bi _4.5 Ti ₄ O ₁₅ may be referred to as “NBT”.
(6) As a sixth aspect of the present invention, the bismuth layered structure compound is a main crystal, and the content of the lamellar structure oxide is 0.5 to 20 mol%.

  The sixth aspect exemplifies a more preferable piezoelectric ceramic composition. This piezoelectric ceramic composition has the advantages of high Curie temperature, low pyroelectricity, excellent piezoelectric characteristics, and high temperature stability.

  (7) The present invention provides, as a seventh aspect (piezoelectric element), a piezoelectric ceramic formed of the piezoelectric ceramic composition according to any one of claims 1 to 6, and an electrode attached to the piezoelectric ceramic. And.

  Since the piezoelectric element according to the seventh aspect includes the piezoelectric ceramic formed of the above-described piezoelectric ceramic composition, it is difficult to be influenced by temperature and can obtain a suitable element output corresponding to the pressure even at a high temperature. it can.

(8) The present invention is characterized in that the piezoelectric element according to claim 7 is provided as an eighth aspect (sensor for an internal combustion engine).
Since the internal combustion engine sensor according to the eighth aspect includes the above-described piezoelectric element, even when the internal combustion engine (for example, a vehicle engine) is used for a purpose such as a pressure sensor or a knocking sensor, the combustion pressure or knocking can be accurately performed. Can be detected.

  Furthermore, using the output of the sensor for the internal combustion engine, it is used for misfire detection, EGR control (exhaust gas recirculation control), optimum mixture ratio control, exhaust gas countermeasure, MBT control (optimum ignition timing control for maximum torque), etc. Can do.

  (9) This invention is a manufacturing method of the piezoelectric ceramic composition of any one of the said Claims 1-6 as a 9th aspect (manufacturing method of a piezoelectric ceramic composition), Comprising: Said Ti is included. Mixing a raw material of lamellar structure oxide and calcining to produce a first powder; mixing a raw material of the bismuth layered structure compound and calcining to produce a second powder; and And a step of producing the piezoelectric ceramic composition by mixing, molding and firing the first powder and the second powder.

  According to this manufacturing method, since the first powder and the second powder are separately produced, each composition can be managed more strictly. As a result, the yield of the piezoelectric ceramic composition can be improved.

It is a perspective view which shows the piezoelectric element as one Embodiment of this invention. It is sectional drawing which fractures | ruptures and shows the pressure sensor for internal combustion engines as one Embodiment of this invention along an axial direction. It is a flowchart which shows the manufacturing method of the piezoelectric element in one Embodiment of this invention. It is a graph which shows the relationship between temperature and the change rate of a piezoelectric constant (d33).

Hereinafter, modes for carrying out the present invention will be described.
[Piezoelectric ceramic composition]
The piezoelectric ceramic composition as one embodiment of the present invention is a piezoelectric ceramic composition having a lamellar structure oxide containing Ti and a bismuth layered structure compound.

  Here, the lamellar structure oxide is an aggregate of fine scale-like, plate-like, and plate-like oxides (showing a layered structure when a certain amount is arranged in a certain direction). It exists as crystals.

As the lamellar structure _{oxide, A 1-x Ti 1-} x B 1 + x O 5 ( element A at least one kind of alkali metal, element B Nb and Ta, x is arbitrary) can be adopted.
Here, as an alkali metal of the element A, K (potassium), R (rubidium), Cs (cesium), etc. are mentioned. The element B includes at least one of Nb (niobium) and Ta (tantalum).

Further, the range of x is arbitrary, but when 0 ≦ x ≦ 0.15, the structure of the lamellar structure oxide is stabilized, and a uniform crystal phase can be obtained.
As the crystalline phase of the lamellar structure oxide described above, KTiNbO ₅ , K _0.90 Ti _0.90 Nb _1.10 O ₅ , K _0.85 Ti _0.85 Nb _1.15 O ₅ , RbTiNbO ₅ , Rb _{0 .90} Ti _0.90 Nb _1.10 O ₅ , Rb _0.85 Ti _0.85 Nb _1.15 O ₅ , CsTiNbO ₅ , Cs _0.90 Ti _0.90 Nb _1.10 O ₅ , KTiTaO ₅ , CsTiTaO ₅ etc. are mentioned.

  From the viewpoint of the structural stability of the crystalline phase of the lamellar structure oxide, the coefficient x satisfies 0 ≦ x <0.15 when the element A is K (potassium) or Rb (rubidium). When element A is Cs (cesium), it is preferable to satisfy 0 ≦ x ≦ 0.10. If K (potassium) is selected as the element A and Nb (niobium) is selected as the element B, a piezoelectric ceramic composition that is inexpensive and excellent in piezoelectric characteristics can be obtained.

The typical composition of this lamellar structure oxide is K _0.85 Ti _0.85 Nb _1.15 O ₅ . Since this crystal phase contains Nb, Ti, and K as main metal components, the crystal phase made of this material may be referred to as “NTK”.

The bismuth layered structure compound is a compound having a crystal structure in which [(Bi ₂ O ₂ ) ²⁺ ] and [(X _m-1 Ti _m O _{3m + 1} ) ²⁻ ] are alternately layered, Present as crystals in the piezoelectric ceramic composition.

  X in the formula is Na (sodium), K (potassium), Ca (calcium), Sr (strontium), Ba (barium), Bi (bismuth), and m is an integer of 1 to 8.

As the bismuth layer structure _compound, when the _{aNa 2 O-bBi 2 O 3} -cTiO 2, 0.030 ≦ a ≦ 0.042,0.330 ≦ b ≦ 0.370,0.580 ≦ c ≦ 0 .640 composition can be employed.

Here, a, b, and c are molar ratios of the respective oxides to the total content of oxides (Na ₂ O, Bi ₂ O ₃ , TiO ₂ ). This is suitable because of its high piezoelectric constant.

As the bismuth layered structure compound, Na _0.5 Bi _4.5 Ti ₄ O ₁₅ type crystal (NBT) is preferably used as the main crystal. Thereby, excellent heat resistance and piezoelectric constant can be obtained.
Here, the main crystal means that a bismuth layered structure compound is substantially a main component in an X-ray diffraction chart obtained by X-ray diffraction measurement (XDR) of the piezoelectric ceramic composition.

Examples of the bismuth layered structural compound include those other than those described above, for example, SrBi ₂ Nb ₂ O ₉ , SrBi ₂ TaO ₉ , BaBi ₂ Nb ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Bi ₄ Ti ₃ O ₁₂ , CaBi. ₄ Ti ₄ O ₁₅ , SrBi ₄ Ti ₄ O ₁₅ , BaBi ₄ Ti ₄ O ₁₅ , K _0.5 Bi _4.5 Ti ₄ O ₁₅ , Sr ₂ Bi ₄ Ti ₅ O ₁₈ , Ba ₂ Bi ₄ Ti ₅ O ₁₈ Is mentioned.

Moreover, as a piezoelectric ceramic composition, a bismuth layered structure compound is used as a main crystal, and the content of lamellar structure oxide can be in the range of 0.5 to 20 mol%.
Within this range, high Curie temperature, low pyroelectricity, high piezoelectric characteristics (piezoelectric constant), and high temperature stability can be realized in a well-balanced manner.

  The piezoelectric ceramic composition as an embodiment of the present invention includes Cu (copper), Ni (nickel), Co (cobalt), Fe (iron), Mn (manganese), Cr (chromium), and Zr (zirconium). , Ag (silver), Zn (zinc), Sc (scandium), Bi (bismuth) may be included.

Even when these metal elements are added, it is possible to obtain a piezoelectric ceramic composition having excellent piezoelectric characteristics (particularly the piezoelectric constant d33).
The total content of these additive metals is preferably 5 mol% or less, and more preferably 1 mol% or less. If the total content of the additive metals exceeds 5 mol%, the piezoelectric characteristics may be deteriorated.

[Piezoelectric element]
A piezoelectric element according to an embodiment of the present invention includes a piezoelectric ceramic formed of the above-described piezoelectric ceramic composition and an electrode attached to the piezoelectric ceramic.

  The piezoelectric ceramic (piezoelectric body) is a portion that exhibits piezoelectric characteristics in the piezoelectric element. The shape and size of the piezoelectric ceramic are not particularly limited, and it is preferable that the piezoelectric ceramic is appropriately selected according to the pressure-sensitive use and the oscillation use. In particular, for pressure-sensitive applications, the planar shape may be various shapes such as a flat plate shape such as a square shape or a circular shape, a flat plate shape with a through hole provided in the central portion in the thickness direction, a prismatic shape, or a cylindrical shape. Moreover, the piezoelectric element of the present invention may be configured by laminating a plurality of piezoelectric ceramics having these shapes.

  The electrode is a conductor layer formed in contact with the surface of the piezoelectric ceramic. When the piezoelectric ceramic is plate-shaped, each of these electrodes may be formed on one surface and the other surface thereof, and each electrode may be formed on the same surface of the piezoelectric ceramic. Further, the shape, size, material, and the like of the electrode are not particularly limited, and it is preferable that the electrode be appropriately selected depending on the size, application, and the like of the piezoelectric ceramic. The shape of the electrodes may be planar, and in particular, when each of the pair of electrodes is formed on the same surface of the piezoelectric body, it may be comb-shaped or half-moon shaped. The method for forming this electrode is not particularly limited, but it is usually obtained by applying a conductive paste to a desired surface of a piezoelectric body and then baking it.

  Here, an example of the piezoelectric element 1 is shown in FIG. As shown in the figure, the piezoelectric element 1 is formed in a disk shape, and a disk-shaped piezoelectric ceramic 3 made of the piezoelectric ceramic composition of the present invention at the center and the thickness direction of the piezoelectric ceramic 3 A thin disc-shaped conductor layer (a pair of electrodes) 5 and 7 is provided on each of the front and back surfaces.

  For example, the electrodes 5 and 7 are obtained by applying a conductive paste to a polished surface obtained by parallel polishing the surface of a sintered body made of the piezoelectric ceramic composition of the present invention, and baking this (for example, 600- (800 ° C. for 10 minutes). The conductive paste can be prepared using glass frit, a conductive component, and an organic medium. By including the glass frit, the bonding strength between the piezoelectric body and the electrode can be improved.

  As the conductive component, a powder made of noble metal such as silver, gold, palladium, platinum, a mixed powder containing two or more of these powders, a powder made of an alloy of two or more noble metals, or the like can be used. In addition, powders made of copper, nickel, etc., or mixed powders thereof, and powders made of alloys of these metals can also be used.

In addition, the piezoelectric ceramic composition in one embodiment of the present invention can be used as an ultrasonic vibrator and a cutting tool in addition to the piezoelectric element.
Moreover, the piezoelectric ceramic composition and the piezoelectric element according to an embodiment of the present invention can be widely used for vibration detection applications, pressure detection applications, oscillation applications, piezoelectric device applications, and the like. For example, sensors for detecting various vibrations (knock sensors, combustion pressure sensors, etc.), piezoelectric devices such as vibrators, actuators, filters, etc., high voltage generators, micro power supplies, various driving devices, position control devices, vibration suppression devices, It can be used for fluid discharge devices (such as paint discharge and fuel discharge). In addition, the piezoelectric ceramic composition and the piezoelectric element according to the embodiment of the present invention are particularly suitable for applications requiring excellent thermal durability (for example, a knock sensor and a combustion pressure sensor).

[Internal combustion engine sensor]
One embodiment of the present invention is a sensor for an internal combustion engine including the piezoelectric element.
An example of the internal combustion engine sensor is a pressure sensor (see FIG. 2) for detecting the fuel pressure in the engine cylinder described in JP-A-5-172680.

  For example, as shown in FIG. 2, the internal combustion engine sensor (that is, the internal combustion engine pressure sensor) 11 has a male screw portion 13 on the outer periphery of the lower end portion, a hexagonal portion 15 on the outer periphery of the upper end portion, and a shaft hole 17 at the center of the shaft. A cylindrical metal shell 19 having the above is provided.

  In the shaft hole 17, a metal plate 21, a first terminal member 23, a (disk-shaped) piezoelectric element 25, a second terminal member 27, and an electrical insulating ring 29 are sequentially arranged in layers from the tip side. The metal shell 19 is electrically insulated by an insulating material 31 arranged around these laminates. An annular member 33 is disposed on the upper end side of the electrical insulating ring 29, and a metal sleeve 35 is fitted to the rear end of the metal shell 19.

  Further, the upper surface of the second terminal member 27 is connected to the core wire 39a of the signal carrying cable 39 (through the annular member 33 and the metal sleeve 35) via the connecting hand 27a and the insulation conducting relay wire 37. Has been.

On the other hand, a pressure transmission rod 41 is inserted at the distal end side of the shaft hole 17, and the upper end side thereof is pressed against the metal plate 21, and the lower end side is fixed to the metal diaphragm 43.
Accordingly, the electrode on the upper surface side of the piezoelectric element 25 is connected to the core wire 39a of the signal carrying cable 39 via the second terminal member 27 and the relay conducting wire 37, and the electrode on the lower surface side is connected to the first terminal member. 23, the metal plate 21, and the pressure transmission rod 41 are connected to the metal shell 19.

  The pressure sensor 11 for an internal combustion engine is configured using the piezoelectric element 25 that has excellent piezoelectric characteristics and does not have a sudden characteristic change between −50 ° C. and + 350 ° C., for example. And high heat durability.

[Method for producing piezoelectric ceramic composition]
In the present invention, as a method for producing a piezoelectric ceramic composition, for example, a step of mixing a raw material of a lamellar structure oxide containing Ti and calcining to produce a first powder; and the bismuth layered structure compound The above-mentioned piezoelectric ceramic composition is prepared by mixing the raw materials and calcining to produce the second powder, and mixing, molding and firing the first powder and the second powder. The manufacturing method which has the process to do is employable.

For example, a predetermined metal is used so that the composition ranges of the target NBT (Na _0.5 Bi _4.5 Ti ₄ O ₁₅ ) and NTK (K _0.85 Ti _0.85 Nb _1.15 O ₅ ) are obtained. After preparing mixed powders (oxides, carbonates, hydrogen carbonates, nitrates, etc.) containing elements, calcining is performed at a temperature lower than the firing temperature to obtain calcined powders of NBT and NTK. Thereafter, NBT and NTK are mixed in a predetermined amount and then fired at a predetermined firing temperature.

Below, suitable embodiment of the manufacturing method of this piezoelectric ceramic composition is described in detail.
As shown in FIG. 3, in step T110, as raw materials for the mother phase (NBT phase), Na ₂ CO ₃ powder as a Na source, Bi ₂ O ₃ powder as a Bi source, and TiO ₂ powder as a Ti source are prepared. To do.

  Thereafter, each raw material powder is weighed so as to be within the above composition range, and wet mixed by a mixer (such as a ball mill) together with a dispersion medium (such as ethanol) to obtain a slurry (slurry). Next, the obtained slurry is dried to obtain the raw material mixed powder.

Then, in process T120, the said raw material mixed powder is calcined and it is set as a mother phase calcined product (2nd powder).
On the other hand, in Step T130, as a _secondary phase (NTK phase) raw material, K ₂ CO ₃ powder, Rb ₂ CO ₃ powder, Cs ₂ CO ₃ powder, TiO ₂ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, etc. Necessary ones are selected from the raw materials, and weighed according to the value of the coefficient x in the subphase composition formula.

Then, ethanol is added to these raw material powders, and wet mixing is preferably performed for 15 hours or more in a ball mill to obtain a slurry.
In Step T140, the mixed powder obtained by drying the slurry is calcined at 600 to 1000 ° C. for 1 to 10 hours, for example, in an air atmosphere to generate a subphase calcined product (first powder).

In Step T150, the mother phase calcined product and the subphase calcined product are weighed so that a piezoelectric ceramic composition having the desired composition can be obtained, and then pulverized and mixed by adding a dispersant, a binder and ethanol in a ball mill. To make a slurry. In addition, when adding an additive metal, a necessary one is selected from CuO powder, Fe ₂ O ₃ powder, NiO powder, ZrO powder, Cr ₂ O ₃ powder, MgO ₂ powder, CoO powder, and weighed. And mix with the slurry. Note that this slurry may be calcined once again and pulverized and mixed.

  Thereafter, the slurry is dried, granulated, and uniaxially pressed at a pressure of 20 MPa, for example, and formed into a desired shape. Thereafter, for example, CIP processing (cold isostatic pressing) is performed at a pressure of 150 MPa to obtain a CIP press body.

  In step T160, the obtained CIP press body is fired by holding, for example, at 900 to 1300 ° C. for 1 to 10 hours in an air atmosphere to obtain a piezoelectric ceramic formed of a lead-free piezoelectric electromagnetic composition. This firing may be performed in a reducing atmosphere or an air atmosphere.

In step T170, the piezoelectric ceramic is processed according to the dimensional accuracy required for the piezoelectric element. For example, the surface is polished in parallel.
In step T180, a conductive paste is applied to the polished surface of the piezoelectric ceramic thus obtained and baked (for example, baked at 600 to 800 ° C. for 10 minutes) to form an electrode.

The conductive paste can be prepared using glass frit, a conductive component, and an organic medium. By including the glass frit, the bonding strength between the piezoelectric ceramic and the electrode can be improved.
As the conductive component, a powder made of noble metal such as silver, gold, palladium, platinum, a mixed powder containing two or more of these powders, a powder made of an alloy of two or more noble metals, or the like can be used. In addition, powders made of copper, nickel, etc., or mixed powders thereof, and powders made of alloys of these metals can also be used.

  In step T190, a polarization process is performed. The polarization treatment is usually placed in an insulating environment maintained at a predetermined temperature {for example, in a highly insulating liquid (such as silicone oil or fluorinate liquid kept at 25 to 250 ° C.)}, and 1 to This can be done by applying an electric field of 10 kV / mm for 1 to 60 minutes.

Next, examples of the present invention will be described.
a) As an example of the present invention (product of the present invention), a sample having a composition of 0.95NBT-0.05NTK + 0.5M was prepared by the method for manufacturing a piezoelectric ceramic composition described above (note that the numbers are molar ratios). , M is an external formulation).

Here, M is a metal element of Co, for example. In addition, the shape of a sample is a disk shape of diameter 3mm x thickness 1mm.
And the characteristic (piezoelectric constant d33, Curie temperature, pyroelectric amount, temperature stability) of the piezoelectric ceramic composition of this sample was measured.

  Specifically, the piezoelectric constant d33 was measured in accordance with EMAS6100 using a d33 meter, the Curie temperature was determined by the change in capacitance with respect to the temperature, and the pyroelectric amount was measured in accordance with JIS1651. The temperature stability is the rate of change of the piezoelectric constant d33 at -50 to + 350 ° C, and was determined by the rate of change based on the d33 value at 20 ° C.

In addition, as a conventional product, a piezoelectric body made of ZnO (Comparative Example 1), quartz crystal (Comparative Example 2), and PbTiO ₃ (Comparative Example) was prepared, and the characteristics were examined.
The results are shown in Table 1 below.

  As is clear from Table 1, the sample of the present invention (product of the present invention) has a large piezoelectric constant (compared to Comparative Examples 1 and 2) and a high Curie temperature (compared to Comparative Examples 2 and 3). Features of low pyroelectricity (compared to comparative example 3), high temperature stability (compared to comparative examples 1 and 3), lead-free, and low price (compared to comparative examples 1 and 2) You can see that

That is, it can be seen that the product of the present invention is a piezoelectric material having a good balance of properties and excellent overall properties as a piezoelectric material.
On the other hand, in Comparative Examples 1 to 3, it can be seen that any of the characteristics is bad and the balance of the characteristics as a piezoelectric material is poor.

  b) Moreover, the piezoelectric ceramic composition of each sample (No. 1-26) of the range of this invention was produced with the manufacturing method of the piezoelectric ceramic composition mentioned above using the material of the following Table 2. That is, each piezoelectric ceramic composition was manufactured by the method for manufacturing a piezoelectric ceramic composition described in the above-described embodiment, using a material adjusted to be the piezoelectric ceramic composition of each sample.

In addition, the shape of a sample is a disk shape of diameter 3mm x thickness 1mm.
For each sample, the crystal phase constituting the piezoelectric ceramic composition is specified by X-ray diffraction (XRD), the main crystal (parent phase) is a bismuth layered structure compound such as NBT, It was confirmed that the (subphase) is a lamellar structure oxide such as NTK. Moreover, the element contained in the piezoelectric ceramic composition and the concentration of the element were confirmed by X-ray fluorescence analysis (XRF).

Further, the piezoelectric constant (d33) and pyroelectric amount of each sample were measured in the same manner as described above, and the pyroelectric amount / piezoelectric constant was calculated. In addition, the addition amount of an additional metal is external mixing.
The results are shown in Table 2 below. In Table 2, the composition of the mother phase, the ratio of the mother phase, the composition of the subphase, and the ratio of the subphase are also described.

  The piezoelectric constant (d33) in Table 2 is preferably 10 [pC / N] or more as a piezoelectric material. Moreover, the value of pyroelectric amount / piezoelectric constant (d33) indicates that it is less susceptible to temperature change, and the smaller this value is, the more preferable it is as a piezoelectric material.

  From Table 2, each sample of the present invention has a large piezoelectric constant of 11 [pC / N] or more, a small pyroelectric amount of 523 [pC / ° C.] or less, and a pyroelectric amount / piezoelectric constant (d33) value of 25. Therefore, it can be seen that it has preferable characteristics as a piezoelectric material.

  As can be understood from Table 2, the additive metals include Cu (copper), Ni (nickel), Co (cobalt), Fe (iron), Mn (manganese), Zn (zinc), Cr (chromium), Even if it contains at least one metal element of Sc (scandium) and Ag (silver), a piezoelectric ceramic composition having sufficiently good characteristics can be obtained.

  c) Furthermore, using the sample No. 1 in Table 2 above, place the sample in a temperature-variable environmental tester, and determine the rate of change of the piezoelectric constant (d33) at each temperature by the resonance anti-resonance method according to EMAS6100. Examined. The rate of change of the piezoelectric constant is a ratio (ratio) with the d33 value at each temperature when the piezoelectric constant (d33) at 20 ° C. is used as a reference.

The result is shown in FIG.
As is apparent from FIG. 4, even when the temperature is changed from −50 to + 350 ° C., for example, the piezoelectric constant change rate is as small as 2% or less.

  Furthermore, as described above, in the piezoelectric ceramic composition of the present invention, since the Curie point is 500 ° C. or higher, the piezoelectric characteristics can be maintained even when exposed to a temperature range higher than 350 ° C. . Therefore, the piezoelectric ceramic composition (piezoelectric element) of the present invention is not easily affected by the external temperature and can be suitably used for a sensor for an internal combustion engine.

In addition, this invention is not limited to the said embodiment and an Example at all, and it cannot be overemphasized that it can implement with a various aspect in the range which does not deviate from this invention.
For example, in the above-described embodiment, the pressure sensor is shown as an application of a sensor for an internal combustion engine using a piezoelectric element. However, the piezoelectric element can be used for an application such as a knocking sensor or an acceleration sensor.

DESCRIPTION OF SYMBOLS 1,25 ... Piezoelectric element 3 ... Piezoelectric ceramic 5,7 ... Electrode 11 ... Pressure sensor for internal combustion engines

Claims (9)

  A piezoelectric ceramic composition comprising a lamellar structure oxide containing Ti and a bismuth layered structure compound. The lamellar structure oxide is A _1-x Ti _1-x B _{1 + x} O ₅ (the element A is an alkali metal, the element B is at least one of Nb and Ta, and x is arbitrary). Item 2. The piezoelectric ceramic composition according to Item 1.   The piezoelectric ceramic composition according to claim 2, wherein x satisfies 0 ≦ x ≦ 0.15. When the bismuth layer structure compound is aNa ₂ O—bBi ₂ O ₃ —cTiO ₂ , 0.030 ≦ a ≦ 0.042, 0.330 ≦ b ≦ 0.370, 0.580 ≦ c ≦ 0. It is 640, The piezoelectric ceramic composition of any one of Claims 1-3 characterized by the above-mentioned. The piezoelectric ceramic composition according to any one of claims 1 to 4, wherein the Na _0.5 Bi _4.5 Ti ₄ O ₁₅ type crystal is a main crystal.   The piezoelectric ceramic composition according to any one of claims 1 to 5, wherein the bismuth layered structure compound is a main crystal, and the content of the lamellar structure oxide is 0.5 to 20 mol%.   A piezoelectric element comprising: a piezoelectric ceramic formed of the piezoelectric ceramic composition according to any one of claims 1 to 6; and an electrode attached to the piezoelectric ceramic.   An internal combustion engine sensor comprising the piezoelectric element according to claim 7. A method for producing a piezoelectric ceramic composition according to any one of claims 1 to 6,
Mixing the raw material of the lamellar structure oxide containing Ti and calcining to produce a first powder;
Mixing the raw materials of the bismuth layered structure compound and calcining to produce a second powder;
Mixing the first powder and the second powder, forming and firing to produce the piezoelectric ceramic composition;
A method for producing a piezoelectric ceramic composition, comprising:

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