High pressure phase transition in FeTe₂O₅Cl

Abstract

Raman and optical absorption spectra of FeTe 2 O 5 Cl at pressures (P) up to 5.9 GPa were measured in order to identify the point of pressure-induced structural phase transition and to compare the vibrational and optical properties of FeTe 2 O 5 Cl to those of FeTe 2 O 5 Br. The structural phase transition was recognized by noticeable changes in the Raman intensities and peak positions at pressure between 1.1 and 1.6 GPa. During the absorbance measurements, a sudden decrease of the band gap value, which is also an indicative of the pressure-induced phase transition, was observed at pressure between 1.5 and 1.9 GPa. The pressure coefficient of the band gap of FeTe 2 O 5 Cl was about À0.118 eV Á GPa À1 at pressures below 1.5 GPa, while the band gap decreases quadratically with pressure (whenand C ¼ À0.003 eV Á GPa À2 ) after the phase transition.