Relaxational behavior of the piezoelectric constant and the electrostriction constant in polymers

Abstract

Abstract Piezoelectricity in polymer films is classified by its mechanism into three groups: A-1, intrinsic piezoelectricity due to internal strain in nonpolar crystals; A-2, intrinsic piezoelectricity due to the strain-dependence of the spontaneous polarization in polar crystals; and B, piezoelectricity due to the heterogeneity of macroscopic strain. The relaxational behavior of piezoelectricity in Type A-1 is discussed for two cases: (a) the piezoelectric phase is relaxing, and (b) the piezoelectric phase is nonrelaxing but the nonpiezoelectric phase is relaxing. For Case a, a thermody-namic theory is developed, yielding relations among relaxation strengths of piezoelectric constant, dielectric constant, and elastic modulus. For Case b, on the other hand, the inequalities e″/e′ 0 are verified for a generalized composite model of two phases, where e′ — ie” and d′ — id″ are complex piezoelectric stress and strain constants, respectively. Relaxational behavior of the piezoelectric constant ...