Raman study of order‐disorder transition of bipolarons in Ti₄O₇

Abstract

Abstract We have studied the phase transition of bipolarons in Ti 4 O 7 by means of Raman spectroscopy. It is found that on warming across the phase transition, the Raman spectrum shows distinct changes, i.e., broadening of the linewidths, decrease in the phonon frequencies, and appearance of the fine structure. These features indicate the existence of structural disorder above the transition temperature, and hence are consisitent with a model that the phase transition is an order‐disorder transition of bipolarons. The mechanism of the line broadening is discussed in relation to the bipolaron motion in the disordered phase. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)