Low temperature Raman study of Ca3Co2O6

TL;DR

This study investigates the low temperature vibrational properties of Ca3Co2O6 using Raman spectroscopy and lattice dynamics calculations, revealing a possible structural distortion below 52K that affects phonon modes.

Contribution

It provides the first detailed Raman analysis of Ca3Co2O6 at low temperatures and suggests a structural transition involving octahedral distortion around 52K.

Findings

Mode frequencies increase as temperature decreases.

Abrupt changes in peak position and FWHM at 52K.

Possible lifting of degeneracy due to octahedral distortion.

Abstract

We present low temperature Raman measurements on Ca3Co2O6. Shell model lattice dynamics calculations were done to determine the vibrational pattern of the expected Raman modes. In the temperature window 300K to 52K the mode frequencies and the full width at half maxima (FWHM) of the modes vary in an expected fashion, i.e., the mode frequencies shift to higher values and the FWHM decreases with lowering of temperature. At about 52K (T *) there happens an abrupt change in both the peak position and FWHM. The peak positions show a sudden softening while FWHM increases abruptly. To explain these spectral features we postulate that below T * the degeneracy of the high symmetry Eg is lifted due to the possible distortion of the CoOO6 octahedra.