Spectroscopic Raman study of trifluoroperovskites of ammonium under high pressure


The compounds NH$_4M$F$_3$ ($M$ = Mg, Zn, Co, Mn, Cd) have the cubic perovskite structure at high temperature, distorting to quasi-tetragonal symmetry at lower temperatures (fig. 1). In a previous communication /1/, some discrepancies between the electrostatic model and experimental data were discussed, mainly the high barrier (2000 K) to rotation of NH$_4$ groups in NH$_4$CdF$_3$.

Heidemann A., Magerl A., Richter D., Prager M., Springer T. (eds), Quantum Aspects of Molecular Motions in Solids (Springer Proceedings in Physics, Springer, Berlin, Heidelberg), vol 17