| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1992: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1991: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
Traveling Solvent Floating Zone method that is a kind of the infrared heating floating zone method with the use of the flux-growth technique can be utilized to obtain oxide single-crystals that crystallize incongruently from the solvent. Present authors had been working to grow 214-type superconducting copper oxide single-crystals and related oxide single-crystals by the TSFZ method and had studied the detailed crystal structures by means of x-ray and neutron diffraction measurements. It was difficult but possible, to obtain small and low quality 214-type oxide single crystals. Their simple crystal structures and relatively broad first crystalization field in the phase diagram might have made the single-crystal growth easier relative to the other complex superconducting oxides. But we could not grow high quality high-Tc single-crystals. Our computer simulation indicated that it was not only crucial to control temperature gradient in the feed rods appropriately, particularly near the mo
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lten zone, but also crucial to keep the chemical composition of the molten zone rigidly throughout the growth process. It was planed to equip a conventional infrared heating floating zone furnace with a computer controlled feed rod driving mechanism to traverse the molten floating zone across the sintered oxide feed rod at an optimized speed which changes non-linearly from the seeding regime to the ending regime. By the Grant-in-Aid for Scientific Research(c) from the ministry of education, science and culture, we could introduce a personal computer controlled feed rod driving mechanism for our infrared floating zone furnace, Nichiden-Machinary-SC4. After intensive efforts to grow good single-crystals, it was found that there were two essential factors for the successful growth. The first was the packing density of the feed rods. The higher the packing density, the better became the grown crystals. It was concluded that the feed rods must be made from finely pulvelized oxide powders in which each grain has a size less than 5mum in diameter. The powders must have the same chemical compositions as the grown single-crystals. When the packing density of the feed rods may be low, the chemical compositions of the molten zone may be changed during the growth and a part of the molten oxide and the solvent, e.g. molten CuO flux plus target oxides, would be penetrated into the loose feed rods. The second point was the temperature gradient in the feed rod in the vicinities of molten floating zone. The steeper the temperature gradient, the better became the quality of the grown crystals. To obtain steep temperature gradient, the physical design of the infrared bulbs set at the focus points of the oval reflectors was optimized. Shading of a part of the reflectors caused similar effect. At the end of the efforts, good single-crystals have been grown repeatedly. The yield of the good single-crystals has sharply increased as high as 90% in these days. High-T_cLa_<1.8>Sr_<0.2>CuO_4
At this stage, we can conclude that we succeeded to obtain a growth technique for the 214-type high-T_c oxide single-crystals as well as an appropriate growth equipment by the Grant-in-Aid for Scientific Research(c) from the ministry of education, science and culture during 1991 through 1993. Less
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