# perovskite

## Raman Spectroscopy of the Ammonium Ion in NH$_4$ZnF$_3$ and NH$_4$MnF$_3$ Perovskites: Temperature Dependence

The Raman spectra corresponding to the internal vibrations of the ammonium ion in NH$_4$MnF$_3$ and NH$_4$ZnF$_3$ single crystals have been measured from 10 to 300 K. The spectra clearly show the existence of a structural phase transition from cubic …

## Raman Spectroscopy of NH$_4$MnCl$_3$ Crystal

The Raman spectra of the NH$_4$MnCl$_3$ crystal above and below the crystallographic phase transition are given for both the lattice and the ammonium modes. The results are discussed in terms of the structure of the crystal lattice and its influence …

## 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 …

## Absorption Spectra of NH$_4$MnCl$_3$ and NH$_4$MnF$_3$

The absorption spectra of NH$_4$MnCl$_3$ and NH$_4$MnF$_3$ crystals have been measured down to 10 K in the 250 to 600 nm region. The observed bands are assigned to electronic transitions from the $^6A_{1g}$(S) ground state to various excited levels …

## Dynamics of the NH$_4^+$ Ion in ABX$_3$ Perovskites

The Raman and IR spectra of NH$_4$MnF$_3$, NH$_4$ZnF$_3$ and NH$_4$MnCl$_3$ have been measured in order to study the internal vibration modes of NH$_4^+$ in different surrounding conditions. The internal force constants have been determined and …

## Espectroscopía Raman de cristales con grupos moleculares: NH$_4$MX$_3$ y MX$_2$$·6H_2O [Raman Spectroscopy of Crystals with Molecular Groups: NH_4MX_3 and MX_2$$·$6H$_2$O]

This thesis is an exhaustive work on the structural properties and vibrations of the ammonium ion in cubic perovskites and the water molecule in transition metal hydrates. Symmetry and frequencies of vibrational modes have been determined at …