Phase transition of titanium dioxide under various pressures

Abstract

Prepressed TiO 2 specimens (anatase) were studied at pressures from 3.8 to 24 kbars at temperatures from 20° to 1000°C for the anatase-rutile phase transition, using a “belt”-type high pressure apparatus. Discontinuous changes in electrical resistance (a.c. and d.c.) of the TiO 2 at various temperatures under isobaric conditions were used to define the phase diagram at pressures > 1 bar. Isothermal phase-transition studies at 1 bar pressure were carried out at 880°–950°C. The phase equilibria at this pressure were determined from X-ray diffraction data at high temperatures, and after quenching to room temperature. The irreversible anatase-rutile phase transition was found to follow a slope dT dP = −0.02 degrees bar −1. The enthalpies of transformation, calculated from the slope, were found to decrease with increasing pressures and decreasing temperatures. The irreversibility of the anatase-rutile phase transition at high pressures was confirmed by electrical resistance and quenching methods carried out on rutile specimens.