PIEZOELECTRIC CERAMIC AND METHOD OF MANUFACTURING THE SAME

Abstract

There is disclosed a piezoelectric/electrostrictive device which exhibits an excellent piezoelectric characteristic and which has an only small dependence on a temperature so that the piezoelectric characteristic does not easily change with the temperature. A piezoelectric/electrostrictive device includes a piezoelectric/electrostrictive portion made of a piezoelectric ceramic, and electrodes electrically connected to the piezoelectric/electrostrictive portion. The piezoelectric ceramic can reversibly transit to a tetragonal phase and an orthorhombic phase at a phase transition point as a boundary, and the piezoelectric/electrostrictive portion is formed by a polarization treatment performed on conditions that a treatment temperature ranges from a temperature which exceeds the phase transition point of the piezoelectric ceramic to a temperature which is 50° C. higher than the temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph in which strains (ppm) of piezoelectric/electrostrictive device of Example 1 and Comparative Example 1 are plotted with respect to temperatures (° C.);

FIG. 2 is a graph in which strain ratios of the piezoelectric/electrostrictive device of Example 1 and Comparative Example 1 are plotted with respect to the temperatures (° C.);

FIG. 3 is a graph in which dielectric constants of a piezoelectric/electrostrictive device of Comparative Example 2 are plotted with respect to the temperatures (° C.);

FIG. 4 is a graph in which dielectric constants of a piezoelectric/electrostrictive device of Example 2 are plotted with respect to the temperatures (° C.);

FIG. 5 is an XRD chart of a piezoelectric/electrostrictive portion of a piezoelectric/electrostrictive device of Example 3;

FIG. 6 is a sectional view schematically showing one embodiment of a piezoelectric/electrostrictive device of the present invention;

FIG. 7 is a sectional view schematically showing another embodiment of the piezoelectric/electrostrictive device of the present invention;

FIG. 8 is a sectional view schematically showing still another embodiment of the piezoelectric/electrostrictive device of the present invention;

FIG. 9 is a sectional view schematically showing a further embodiment of the piezoelectric/electrostrictive device of the present invention;

FIG. 10 is a graph in which strains (ppm) of piezoelectric/electrostrictive device of Examples 1, 5 and Comparative Example 1 are plotted with respect to the temperatures (° C.); and

FIG. 11 is a graph in which strain ratios of the piezoelectric/electrostrictive device of Examples 1, 5 and Comparative Example 1 are plotted with respect to the temperatures (° C.)

Claims

1. A piezoelectric/electrostrictive device comprising: a piezoelectric/electrostrictive portion made of a piezoelectric ceramic; and electrodes electrically connected to the piezoelectric/electrostrictive portion, the piezoelectric ceramic being configured to reversibly transit to a tetragonal phase and an orthorhombic phase at a phase transition point as a boundary,the piezoelectric/electrostrictive portion being formed by a polarization treatment performed on conditions that a treatment temperature ranges from a temperature which exceeds the phase transition point of the piezoelectric ceramic to a temperature which is 50° C. higher than the temperature.

2. A piezoelectric/electrostrictive device comprising: a piezoelectric/electrostrictive portion made of a piezoelectric ceramic; and electrodes electrically connected to the piezoelectric/electrostrictive portion, the piezoelectric/electrostrictive device being drivable by a driving electric field applied to the piezoelectric/electrostrictive portion in a predetermined direction, the piezoelectric/electrostrictive portion being formed by a polarization treatment performed on conditions that a polarization electric field is applied to the piezoelectric ceramic in a direction reverse to the predetermined direction in which the driving electric field is applied.

3. The piezoelectric/electrostrictive device according to claim 2, wherein the piezoelectric ceramic is configured to reversibly transit to a tetragonal phase and an orthorhombic phase at a phase transition point as a boundary; and the piezoelectric/electrostrictive portion is subjected to the polarization treatment on conditions that a treatment temperature ranges from a temperature which exceeds the phase transition point of the piezoelectric ceramic to a temperature which is 50° C. higher than the temperature.

4. The piezoelectric/electrostrictive device according to claim 1, wherein a composition of the piezoelectric ceramic is represented by the following general formula (1): {Liy(Na1-xKx)1-y}a(Nb1-zTaz)O3  (1),

5. The piezoelectric/electrostrictive device according to claim 1, wherein a difference between a maximum value and a minimum value of a strain ratio in a range of 25 to 70° C. is 0.2 or less, the ratio being represented by a ratio of a minimum value of a strain with respect to a maximum value of the strain.

6. The piezoelectric/electrostrictive device according to claim 1, wherein in the piezoelectric/electrostrictive portion, an absolute value of a difference between a temperature at which a maximum value (ε1) of a dielectric constant measured in a process of raising the temperature is measured and a temperature at which a maximum value (ε2) of a dielectric constant measured in a process of lowering temperature is measured is 15° C. or less.

7. The piezoelectric/electrostrictive device according to claim 1, wherein in a chart of the piezoelectric/electrostrictive portion obtained by measurement performed at 25° C. by an X-ray diffraction process, a ratio between an intensity (S1) of a peak which appears at 2θ=45±1 and an intensity (S2) of a peak which appears at 2θ=46°±1 is in a range of S1:S2=1:5 to 5:1.

8. The piezoelectric/electrostrictive device according to claim 1, wherein in the piezoelectric/electrostrictive portion, a mass ratio between a content (T) of tetragonal crystals and a content (R) of orthorhombic crystals at 25° C. is in a range of T:R=2:8 to 10:0.

9. The piezoelectric/electrostrictive device according to claim 1, wherein the piezoelectric/electrostrictive portion and the electrodes have film-like shapes, respectively, the piezoelectric/electrostrictive device further comprising: a substrate made of a ceramic,the piezoelectric/electrostrictive portion being secured to the substrate directly or via the electrodes.

10. The piezoelectric/electrostrictive device according to claim 1, which is used as an actuator or a sensor.

11. A method of manufacturing a piezoelectric/electrostrictive device t comprising: a piezoelectric/electrostrictive portion; and electrodes electrically connected to the piezoelectric/electrostrictive portion, the method comprising: subjecting, to a polarization treatment, a piezoelectric ceramic configured to reversibly transit to a tetragonal phase and an orthorhombic phase at a phase transition point as a boundary on conditions that a treatment temperature ranges from a temperature which exceeds the phase transition point to a temperature which is 50° C. higher than the temperature to form the piezoelectric/electrostrictive portion.

12. A method of manufacturing a piezoelectric/electrostrictive device comprising: a piezoelectric/electrostrictive portion; and electrodes electrically connected to the piezoelectric/electrostrictive portion, the piezoelectric/electrostrictive device being drivable when a driving electric field is applied to the piezoelectric/electrostrictive portion in a predetermined direction, the method comprising: subjecting, to a polarization treatment, a piezoelectric ceramic configured to reversibly transit to a tetragonal phase and an orthorhombic phase at a phase transition point as a boundary on conditions that a polarization electric field is applied to the piezoelectric ceramic in a direction reverse to the predetermined direction in which the driving electric field is applied.

13. The method of manufacturing the piezoelectric/electrostrictive device according to claim 12, wherein the piezoelectric ceramic is subjected to the polarization treatment on conditions that a treatment temperature ranges from a temperature which exceeds the phase transition point to a temperature which is 50° C. higher than the temperature.