Dielectric and Thermal Study of ${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$S${\mathrm{O}}_4$ and ${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$Be${\mathrm{F}}_4$ Transitions

The behavior of the various dielectric properties, specific heat, and thermal expansion of ${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$S${\mathrm{O}}_4$ and ${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2$Be${\mathrm{F}}_4$ has been studied in detail under various experimental conditions, with particular reference to the ferroelectric transitions in these crystals. The curves of dielectric constant vs temperature do not obey the Curie-Weiss law. The shift of the transition temperature as reported in the literature could not be detected even under extreme experimental conditions. The transition energy and entropy change have been evaluated from a $C_p$ vs $T$ curve. The variation of the lattice parameters and the unit cell volumes with temperature has been measured by the x-ray method.