Pressure-induced crossover between diffusive and displacive mechanisms of phase transitions in single-crystalline α-GeO2 -: art. no. 145503

We present the first example of the phase transition occurring via the different kinetic mechanisms, displacive or diffusive, competing with each other in quartzlike alpha-GeO2 single crystals. Upon room-pressure heating, alpha-GeO2 transforms to the rutile-type phase (the alpha --> r transition) via the diffusive mechanism. With increase of the treatment pressure the diffusive mode of the temperature-induced alpha --> r transition is substituted at approximate to 4 GPa by a displacivelike mode, and then at approximate to 6 GPa the transition type changes from the alpha --> r sequence to a displacive martensiticlike transition to a distorted rutilelike phase (alpha --> r'. A crossover between diffusive and displacive transition modes suggests a new way to control the meso- and nanometer-scale morphology of high-pressure phases.