External field effect on the anisotropy of dielectric permeability of KH_{2}PO_{4} and NaKC_{4}H_{4}O_{6}· 4H_{2}O crystals under high pressure

Abstract

Experimental studies of the effect of temperature, external pressure and electric field on the anisotropy of dielectric permeability of KH 2 PO 4 and NaKC 4 H 4 O 6 · 4H 2 O crystals are performed. The experimental data on the effect of electric field and pressure on the dielectric permeability of Rochelle salt are analyzed in the framework of phenomenological theory with the account of the vicinity of the phase transitions to the double critical point. Coefficients of thermodynamic potential expansion over the order parameter are determined as well as its pressure behaviour is described. The hydrostatic pressure increase is shown to shift the phase transitions in Rochelle salt away from the double critical point.