X-RAY POWDER DIFFRACTION STUDY OF THE PHASE-TRANSITIONS IN TI4O7

A high precision temperature dependent X-ray powder diffraction study has been carried out on Ti4O7 in the temperature range between 180 and 90 K enclosing the metal-insulator and the so-called Ti4O7-Verwey tra nsition. Both transitions are characterized by negative Volume effects as can be deduced from the temperature dependent course of the lattic e parameters. Total strains induced by the formation of the intermedia te phase are about 0.007 and about twice that value in the low tempera ture phase. In successive heating and cooling runs it is observed that the low temperature transition occurs stepwise, possibly related to t he deterioration of the modulated structure.