Dielectric study of the phase transition in NaNH4SeO4·2H2O crystals

The influence of external forces, bias electric field and mechanical shear stress σ6 on electric permittivity εc of NaNH4SeO4·2H2O crystals is reported. The shear stress σ6 influences strongly on electric permittivity εc of the crystal in the ferroelectric phase. The dielectric constant is also measured in the paraelectric phase as a function of electric field at constant temperature. The value of coefficient B (non-linear coefficient) on the basis of the classical state equation was calculated. The B sign and εc(E) dependence point out of the second-order phase transition in this crystal.