Thermal Properties of Ferroelectric NaNH4SO4·2H2O

Specific heat and lattice constants of ferroelectric NaNH 4 SO 4 ·2H 2 O were measured in a wide temperature range covering the transition temperature. The transition entropy was estimated to be Δ S =0.79 cal·mole -1 ·deg -1 . The spontaneous tensile strains were obtained to be x x =5.0×10 -3 , y y =2.1×10 -3 and z z =3.2×10 -3 at -185^° C . The results were discussed thermodynamically with the help of additional results of dielectric measurements made near the transition temperature.