Fundamentals of Mutual Conversion of Electrical Energy and Mechanical Energy by Simultaneously Ferroelectric and Ferroelastic Crystals

The concept “ferroelasticity” is analogous to “ferroelectricity,” mechanical strain and stress in the former corresponding to electric polarization and field in the latter. Crystals which are both ferroelectric and ferroelastic can (in principle) be applied to mutual conversion of electrical energy and mechanical energy. A thermodynamic investigation is made into basic problems in this application–domain structure of the crystal element, optimum conditions for conversion, rate of conversion, and others; here the crystal concerned is assumed to be such that the ferroelasticity may phenomenologically be regarded as induced by the ferroelectricity through piezoelectric coupling or, oppositely, such that the ferroelectricity may phenomenologically be regarded as induced by the ferroelasticity through piezoelectric coupling. For the sake of comparison, the case is also considered where a typical, simple piezoelectric crystal is used instead.