Title: External field effect on the anisotropy of dielectric permeability of KH₂PO₄ and NaKC₄H₄O₆· 4H₂O crystals under high pressure
Author(s):

	A.G.Slivka (Uzhhorod National University, Department of Optics, 54 Voloshyn Str., 88000, Uzhhorod, Ukraine) ,
	V.M.Kedyulich (Uzhhorod National University, Department of Optics, 54 Voloshyn Str., 88000, Uzhhorod, Ukraine) ,
	H.M.Guyvan (Uzhhorod National University, Department of Optics, 54 Voloshyn Str., 88000, Uzhhorod, Ukraine)

Experimental studies of the effect of temperature, external pressure and electric field on the anisotropy of dielectric permeability of KH₂PO₄ and NaKC₄H₄O₆· 4H₂O 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.

Key words: ferroelectrics, phase transition, dielectric permeability, pressure, electric field
PACS: 77.80.Bh, 77.22.Ch, 77.84.Fa

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