Kinetics Studies of Pressure Induced B4 to B1 Phase Transformation in CdSe

John Copley, Princeton University

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Despite playing an important role in transformation processes and microstructural development, the kinetics of pressure induced phase transformations are often poorly understood due to historic defaulting in creating the square wave pressure profiles required to perform classical kinetic experiments in diamond anvil cell devices. We demonstrate that double sided membrane compression, i.e. paired membrane diamond anvil cell (mDAC) compression and decompression, allows for generation of near square pressure profiles, thereby allowing us to perform fixed overpressure kinetic studies when used in conjunction with time-resolved diffraction. We are able to use data from these experiments to constrain the mechanism of the B4 to B1 (wurtzite to rocksalt) as a martensitic, nucleation limited transformation and obtain values of the kinetic rate constant as a function of pressure. We additionally construct predictions of the transformation kinetics for various conditions of compression rate, on the orders of 10-3 to 10 GPa/s, rates achievable through the use of a piezo-electrically driven dynamic diamond anvil cell (dDAC). We compare these predictions to data collected using a dDAC and time-resolved synchrotron X-ray diffraction at Sector 16-ID-B of the Advanced Photon Source.

Abstract Author(s): John Copley, Guoyin Shen, Jesse Smith, Thomas Duffy