Relations between isothermal and adiabatic third‐order material constants of piezoelectric and pyroelectric crystals

摘要

Depending on measurement conditions different choices of independent variables are used in the phenomenological description of piezo‐ and pyroelectricity. Eight different sets of material constants arise in this way on the basis of the commonly employed field variables resulting in a vast number of different but related third‐order constants. To cope with this fact a generalized notation is introduced for them. Starting from the proper rotationally invariant form of the electric Gibbs function and the electric enthalpy, the relations between isothermal and adiabatic third‐order material constants are derived. A numerical estimate for the nonlinear piezoelectric constants of agr;‐quartz is presented.