Synchrotron X-Ray Tomography and PDF Studies for Non-Crystalline Materials Under High-Pressure Conditions

Abstract:

The accurate measurement for equation of state (EoS) of non-crystalline materials under pressure conditions is a long-standing problem. Selected 2 element systems were studied under high pressure via synchrotron microtomographic, x-ray diffraction (XRD) as well as pair distribution function (PDF) techniques using diamond anvil cell and large volume press. Amorphous selenium (a-Se) is a model system for examining pressure effects in amorphous materials because of the wide range of structure and bonding properties. An unexpected pressure-induced dynamic crystallization process associated with a volume expansion in this material at bout 10 GPa was discovered, and one amorphous to amorphous state transitions at about 3.7 - 5 GPa was proposed based on the PDF result. For Ga melt case, which the recent PDF researches showed controversial feature, the origin of this unusual phenomenon is examined using synchrotron microtomographic technique combined with XRD using large volume press, which allowed direct measurement of the EoS of the melting state and detecting solidification. Besides obtaining measured EoS of Ga melt, a possible liquid-to-liquid transition in Ga is founded from the abnormal compressibility of the melt. These examples demonstrated that the combination of synchrotron x-ray tomography and PDF methods offer the powerful tools to investigate the structure and EoS on non-crystalline materials under high-pressure extreme conditions.