Dynamical observation of the pressure-induced structure change

Since synchrotron radiation has been utilized, diffraction studies of structure changes under high pressure have become an extremely active field not only for solid state physics but also for earth sciences. Phase equilibrium in the pressure-temperature diagram has been elucidated by the extensive studies using diamond anvil or mutianvile high pressure apparatus. Recently kinetic studies become more significant subjects in order to comprehend the phase transformation mechanism under the condition of compression. Time-resolved and in situ diffraction study give a brilliant light to the dynamical observation of the pressure-induced structure change. Nonhydrostaticity of compression brings metastable states or intermediate states, which are different from the thermodynamically stable phases, because they are temporary states in the dynamical process. Kinetic study of the pressure-induced transition is discussed in accordance with the in situ observation of time-resolved diffraction measurement. Besides the stress-strain relation, the crystallite size is an effective parameter of phase transition under pressure. Molecular dynamical calculation simulates the high-pressure phase transition. (author)