Additional elements of Ca, Sr, and Ir are added to a single layer lead lanthanum zirconate titanate (PLZT), thereby decreasing a c/a ratio to within a range from 1.00 to 1.008 smaller than a general c/a of a range from about 1.01 to 1.03 generally used in a lead lanthanum zirconate titanate (PLZT) crystal having a crystal structure of a tetragonal system. With this arrangement, a large switching charge Qsw can be obtained without thinning the PLZT layer even when the operation voltage is 3.0 V or less.