Spectroscopic Raman study of trifluoroperovskites of ammonium under high pressure

Resumen

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$_3$.