CHEMICAL VAPOR GROWTH OFβ-FeSi₂ SINGLE CRYSTAL AND IN SITU OBSERVATION OF ITS PHASE TRANSITION UNDER HIGH PRESSURE

Crystal growth technology and crystal structure of high quality β-FeSi₂ single crystals grown from vapor by employing chemical vapor transport technique and its phase transition under high pressure were studied. 1. Single crystals of β-FeSi₂, as new photoeletric and thermoelectric material have been grown from vapor by employing chemical vapor transport technique with iodine as transport agent in a closed ampoule. Needle-like single crystals were gained and Grain-like single crystals were obtained. By changing substrate temperature, tetrahedral high quality β-FeSi₂ single crystals were grown. 2. The effects of orientation of the direction of mass transport in gravity field on the single crystal growth of (β-FeSi₂ were studied. As the angle between gravity and mass transport direction was 900 or 1800, mass transport process was convection-dominated regime. And as the angle between gravity and mass transport direction was 00, it was diffusion-dominated. In convection-dominated cases, morphologies of β-FeSi₂ single crystals were similar and pyramid-like. In the diffusion dominated case, β-FeSi₂ single crystals were lamellate. This shows that the processes of mass transport are different for mass transport direction in gravity field. 3. Temperature dependence of electrical resistivity of β-FeSi₂ single crystals was measured by four-probe method. It was found that electrical resistivity increases with increasing lIT. 4. Phase transition of β-FeSi₂ single crystals at high pressure with Diamond Anvil Cell Apparatus were in situ studied by synchrotron radiation X-ray diffraction. Phase transition began at 4.3GPa and completed at 22GPa. The product of phase transition is tetragonal and its lattice constants are a40.4393nm, and c2.0507.