Title: NON-LINEAR MECHANICAL, ELECTRICAL AND THERMAL PHENOMENA IN PIEZOELECTRIC CRYSTALS
Author(s): F.Warkusz, A.Linek (Institute of Physics, Opole University, 45--052 Opole, Poland)

Mechanical, electrical and thermal phenomena occurring in piezoelectric crystals were examined by non-linear approximation. For this purpose, use was made of the thermodynamic function of state, which describes an anisotropic body. Considered was the Gibbs function. The calculations included strain tensor $\varepsilon_{ij} = f(\sigma_{kl},E_{n},T)$, induction vector $D_{m}=f(\sigma_{kl},E_{n},T)$ and entropy $S = f(\sigma_{kl},E_{n},T)$ as function of stress $\sigma_{kl}$, field strength $E_{n}$ and temperature difference $T$. The equations obtained apply to anisotropic piezoelectric bodies provided that the ``forces'' $\sigma_{kl}$, $E_{n}$, $T$ acting on the crystal are known.

Key words: piezoelectric crystals, thermodynamics, anisotropic bodies, tensors
PACS: 65.40.-b, 77.65.-j, 77.65.Bn, 77.65.Ly, 05.70.Ce