Absence of phase transitions in an oxygen stoichiometric cobaltite, YBaCo4O7

Abstract

Polycrystalline YBaCo4O7 compounds are synthesized by solid state reaction in air atmosphere. X-ray powder diffraction at room temperature indicates its single phase nature. Rietveld refinement of X-ray diffraction data shows distortions in bond lengths in the cobalt-oxygen tetrahedra. Electrical resistivity of YBaCo4O7 suggests a variable range hopping type of conductivity from 80 K up to room temperature. Raman scattering spectra exhibit several broad phonon modes at ambient temperature. Raman spectroscopic measurements are carried out as a function of temperature to look for any structural phase transitions from 80 to 823 K. Raman scattering results show no phase transitions, supporting low temperature conductivity measurements. From temperature variation of Raman spectra, it is found that the structure is stable in the temperature range of present study.