High pressure phase transition in FeTe2O5Cl

Raman and optical absorption spectra of FeTe2O5Cl 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 FeTe2O5Cl to those of FeTe2O5Br. 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 FeTe2O5Cl was about -0.118 eV . GPa(-1) at pressures below 1.5 GPa, while the band gap decreases quadratically with pressure (when E-g = A + B.P + C.P-2, A = 2.391 eV, B = 0.015 eV.GPa(-1), and C = -0.003 eV . GPa(-2)) after the phase transition. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim