Effect of Pressure on Atomic Transport in Covalent Network Materials

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The objective of this investigation is to understand the effects of high pressure on diffusion and crystal growth. The rates of atomic transport in condensed matter are typically reduced by the application of pressure, due to a reduction in the concentration of point defects or free volume. The present research is on a class of materials known as covalent network materials which exhibits enhanced atomic mobility under pressure. The emphasis of the research is to investigate the mechanisms responsible for this behavior. Materials studied include amorphous semiconductors, chalcogenides, and silicate melts and glasses. Measurement of the pressure-dependence of atomic transport provides direct information that cannot be determined by measurement of temperature-dependent transport. Experimental techniques include high pressure melting and phase transformation, x-ray diffraction, ion beam sputtering, Rutherford backscattering, secondary ion mass spectroscopy, and electron microscopy.