| Budget Amount *help |
¥4,100,000 (Direct Cost: ¥4,100,000)
Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1988: ¥3,700,000 (Direct Cost: ¥3,700,000)
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| Research Abstract |
The purpose of this study is to prepare high purity single crystals of niobium triselenide, the typical quasi-one dimensional conductor. They are used for the study of the dynamical properties of charge density waves in media with low defect concentrations. Crystal growth were repeated under various conditions, after careful selection of startinal materials and quartz tubes for gas phase reaction growth. Niobium of 99.9997% purity was used. Sheets of 0.2-0.4 mm thickness were annealed in high vacuum to reduce the oxygen content. Selenium used was of 99.9999% purity. Quartz tubes, with low concentration of Fe and Cu were used. Before sealing the starting materials, quartz tubes were annealed at high temperature and in high vacuum. Clean evacuation system was constructed for sealing the tube, using a cryo-pump and a turbo-molecular pump, the latter being free from residual oil gas because magnetic bearings are used. Relatively large crystals, with the transverse dimensions several tens of micron, were grown at 650-700C with a suitable temperature gradient along the quartz tube. As long as the quantity of starting materials were kept to 0.01 mole, the residual resistance ratio was lower than 250, and its magnitude shows a variation along the sample length. It has been found that the residual resistance ratio has no relation to the concentration of alkaline/OH impurities of quartz tubes. To grow large crystals, suitable magnitude of temperature gradient is necessary; only tiny crystals have been grown when a furnace with high temperature homogeneity was used.
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