Structural Changes in Molten Vb and VIb Metals and Ultra-Sound Propagation.

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We have renewed a gated RF amplifier with the grant and set up a stable ultra-sonic measurement gear, with which we have measured systematically the velocity of sound in various molten alloys at high temperatures. To compliment the ultra-sound measurements, we have measured the density with the gamma-ray attenuation method. Further we have derived the new thermodynamic relations which enable to elucidate the concentration fluctuations induced by local structural changes. During the period of the grand, we have published ten papers in well-established international journals. To proceed the research project, I was reviewed by Dr. C. Bergman at CNRS, Marseille and Dr. F. Sommer at MPI, Stuttgart in 1998.Main results are1. Structural changes in the As-Te system : the phase diagram has been investigated by detecting a minimum in the sound velocity and/or the thermal expansion coefficient as a function of temperature. The minimum has been confirmed up to 60 at.% of As. The transition point i … More n the structural change in the super-cooled molten As has been determined to be 734 ± 6℃ by an extrapolation.2. Structural changes in the molten II b-VI b system : by measuring the sound velocity, it has been shown that the molten CdTe has very stable structure whereas the molten HgTe undergoes continuous structural changes around the melting point. The transition point in the molten HgTe has been determined.3. The thermodynamic relations connecting structural changes and concentration fluctuations in a binary mixture : the new thermodynamic relations which enable to elucidate the concentration fluctuations induced by local structural changes have been derived. Application has been made to show the origin of the looped two-melt phase in the molted S-Te system.The concentration fluctuations induced by structural changes are one of the key points to be clarified to grow high quality crystals of the compound semiconductors. We are planning to investigate systematically the phenomenon by measuring the specific heat as well as the sound velocity and density of molten compound semiconductors at high temperatures. Less