Kinetic control of high pressure phase transitions in anatase TiO2

Understanding the interplay between the thermodynamics and kinetics of phase transition under high pressure is a current challenge in material and physical sciences. Here, we present the structural response of anatase TiO2 up to 20 GPa and over compression rates ranging from 0.03 to 3.61 GPa/s, using a piezo-driven dynamic diamond anvil cell coupled with time-resolved Raman spectroscopy. It is found that the phase evolution of anatase TiO2 follows the expected thermodynamics path (i.e., anatase-* alpha-PbO2-* baddeleyite) regardless of the applied compression rate, however, the formation conditions of high pressure phases are kinetically controlled. Both phase boundaries increase approximately linearly with the logarithm of compression rate, that seems to resolve apparent contradictions between previous high pressure results. We ascribe these to the sluggish transition kinetics of a typical reconstructive transition mechanism, and highlight that the compression rate behaves as the third dimension within a high pressure phase diagram.