Phase Transition Of Amorphous Selenium And Liquid Gallium Under High Pressure

Selenium and gallium, as important semiconductor materials, have richstructural phase transitions under high pressure, which are of fundamental interest.They could stay at non-crystalline state under ambient conditions, where seleniumwill be amorphous solid and gallium as melt at above303K.There have been many studies on the crystallization process of amorphousselenium and liquid gallium, but most of them focused on crystals. We focused onthe experimental study of these two elements in the amorphous state of thepressing process. In a previous study of amorphous selenium, there was anintermediate state which had no detailed conclusions before the pressure come to10.4GPa. When pressurized gallium to2.0GPa, there have been two researchgroups who got quite different conclusions when they tried to get the changes ofcoordination number, volume and density to find the structural changes of galliumusing high energy X-ray diffraction and pair distribution function.In our topic, we used high-pressure X-ray diffraction and microtomographytechniques to get the volume and density changes of gallium directly. Thencompared the conclusion to the previous studies, which pressurize gallium to2.0GPa to get the structural changes using high energy X-ray diffraction and pairdistribution function, to get the correct conclusions about the structure of liquidgallium under high pressure. Our experimental data was close to the resultreported by O.F. Yagafarov et al, which gave a reliable analysis on structurechange of gallium melt under compression.At the same time, we used high energy X-ray diffraction and pair distributionfunction to get the crystallization process of amorphous selenium under highpressure. comparing with the results of X-ray diffraction and microtomography onamorphous selenium, we got reasonable explanation intermediate states ofamorphous selenium before the crystallization. We found the coordination numberand density change of the intermediate states of amorphous selenium were close tomonoclinic structure. The structural phase transitions before crystallization werebetween amorphous to amorphous phase.The combination of high-pressure X-ray diffraction and microtomographytechniques with high-energy X-ray PDF methods, which we used to discover thestructural changes of amorphous materials, provide an effective experimentalmethods in future studies.