12-04U

Recently proposed four-sublattice model for Rochelle salt is enhanced by taking into account piezoelectric coupling with shear strains $\varepsilon_4$, $\varepsilon_5$ and $\varepsilon_6$. Components of polarization vector and of static dielectric permittivity tensor for both mechanically clamped and free crystals, their piezoelectric characteristics and elastic moduli are derived in the mean field approximation. A proper choice of model parameters provides a good quantitative description of the available experimental data for ordinary and deuterated Rochelle salt for these characteristics.