Piezoelectric actuator

A piezoelectric actuator which comprises as a drive source a piezoelectric element in which a pair of electrodes have been formed on a surface of a piezoelectric ceramic member wherein when a voltage is applied to the piezoelectric actuator to drive the piezoelectric actuator under such a condition that the driving voltage have a constant amplitude at an electric field strength of 100 V/mm or more, the piezoelectric actuator satisfies at least one of the following requirements (a) to (c):

• (a) the variation width Wc [%] in an apparent dynamic capacity C [F] due to a change in temperature, which is represented by the following equation (1), should fall within ±11% over a specific temperature range from −30° C. to 80° C. (wherein C [F] denotes the apparent dynamic capacity of the piezoelectric actuator which is calculated by dividing an amount of charge Q [C], which is accumulated in a capacitor, by the voltage V [V] applied to the piezoelectric actuator, when the piezoelectric actuator and the capacitor are connected in series with each other and a voltage is applied to each of the piezoelectric actuator and the capacitor):
• Wc(%)=[{2×Cmax/(Cmax+Cmin)}−1]×100 (1)
• wherein Cmax denotes the maximum value of the apparent dynamic capacity observed at the temperatures ranging from −30° C. to 80° C., and Cmin denotes the minimum value of the apparent dynamic capacity observed at the temperatures ranging from −30° C. to 80° C.;
• (b) the variation width WL [%] in a displacement L [μm] due to a change in temperature, which is represented by the following equation (2), should fall within ±14% over the specific temperature range from −30° C. to 80° C. (wherein L[μm] denotes the displacement of the piezoelectric actuator):
• WL(%)=[{2×Lmax/(Lmax+Lmin)}−1]×100 (2)
• wherein Lmax denotes the maximum value of the displacement observed at the temperatures ranging from −30° C. to 80° C., and Lmin denotes the minimum value of the displacement observed at the temperatures ranging from −30° C. to 80° C.;
• and
• (c) the variation width WL/C[%] in a quotient L/C due to a change in temperature, which is represented by the following equation (3), should fall within ±12% over the specific temperature range from −30° C. to 80° C. (wherein C [F] denotes the apparent dynamic capacity of the piezoelectric actuator, L [μm] denotes the displacement of the piezoelectric actuator, and C [F] is calculated by dividing an amount of charge Q [C], which is accumulated in a capacitor, by the voltage V [V] applied to the piezoelectric actuator, when the piezoelectric actuator and the capacitor are connected in series with each other and a voltage is applied to each of the piezoelectric actuator and the capacitor):
• WL/C(%)=[{2×(L/C)max/((L/C)max+(L/C)min)}−1]×100 (3)
• wherein (L/C)max denotes the maximum value of the quotient L/C observed at the temperatures ranging from −30° C. to 80° C., and (L/C)min denotes the minimum value of the quotient L/C observed at the temperatures ranging from −30° C. to 80° C.;
• and
• wherein the piezoelectric ceramic member is formed with a polycrystalline body whose main phase is an isotropic perovskite compound represented by a general formula {Li2(K1-yNay)1-x}{Nb1-z-wTazSbw}O3 (wherein 0≦x≦0.2, 0≦y≦1, 0≦z≦0.4, 0≦w≦0.2 and x+z+w>0 are established), and is a crystal-oriented piezoelectric ceramic wherein specific crystal faces of each crystal grain constituting the polycrystalline body are oriented.