The ferroelectric phase transition in ammonium sulphate

ESR Study of a Cr5+ Centre in Ferroelectric Ammonium Sulphate

“…The present work on chromate doped (NH4),S04 shows that the sulphate ion is distorted below Tc. Distortion of (SO4),-ion in (NH4),S04 has also been recognized by Jain et al However, t,he former two types of directed bonds appear to be of secondary importance because i) on deuteration, T, is not affected [2] or is negligibly affected by (0.6 & -0.1) K [28]; ii) the 3310 cm-l band associated with NH: ion exhibits comparatively slow change in its intensity near T, [16]; iii) the proton NMR linewidth is not affected by the transition [29]; iv) the transition results in more distorted (S04)2-ions and less distorted NH: ions [30] in the ferroelectric phase in comparison with the respective ones in the paraelectric phase.…”

“…The phase transition in (NH4),S04 has been shown to be of first order [2, 16 to 181. The structural basis for the phase transition is, however, not completely understood so far.…”

A Point Charge Model for the Ferroelectric Transition in Ammonium Sulphate

“…Recently, we have also studied the temperat,ure dependence of integrated intensity of a few extrathermosensitive IR bands of polycryst,alline (KH4)2S04 [22]. I n this paper, we report the computed values of permanent dipole moments (associated with NH:(I), NHi(II), and SO:ions in paraelectric phase at -298 O K and in ferroelectric phase a t -180 O K ) and the spontaneous polarization (in ferroelectric phase a t -180 OK).…”

Linewidth of Phonons in Order–disorder Phase Transitions With Random Telegraph Noise

“…12 So that the spontaneous polarization has been accounted for due to the permanent dipole moment of the distorted ammonium and sulfate ions. 13,14 Since the spontaneous polarization can be related to the damping constant, 15,16 as examplified for the KDP-type crystals, 17,18 the critical behavior of the spontaneous polarization below T c in (NH 4 ) 2 SO 4 directly determines an abrupt change in the linewidths. Regarding an abrupt change in the linewidths of the ν 1 symmetric stretching mode of SO 2− 4 ion, it has been observed from the Raman scattering in ammonium sulfare 19 that it shows rapid and nonlinear broadening above T c .…”