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Heat treatment in a vacuum-sealed system on BiSrCaCu2O x was studied in comparison with that in air. The melting temperature was lowered from 880°C in air to 850°C in the vacuum-sealed system. The formation of the phase with 37 Å c spacing was enhanced in the vacuum-sealed system by heating above the melting temperature and the subsequent annealing in air improved the sharpness of the superconducting transition at 110 K. The heat treatment in the reduced pressure also caused the reduction of the Cu ion and it was suggested that the oxidation state of the Cu ion played an important role in the formation of the phase with 37 Å c spacing.

Partially melted states of Bi-Sr-Ca-Cu-O were investigated by SEM-EDX analysis and X-ray measurements on rapidly quenched samples in which the partially melted states were preserved. The 30 Å phase was found to decompose into a Bi-rich liquid phase and crystalline phases of Sr-Ca-Cu-O in the partial melt. The crystalline phases were assigned to Sr1-x Ca x CuO2 (x\fallingdotseq0.5) or (Ca1-x Sr x )2CuO3 (x

Melting and crystallization behavior of a high-T c compound Ba2YCu3O x was investigated by microstructural observation, and compositional, thermal and X-ray analyses. Because of an incongruent melting, Ba2YCu3O x decomposes into a solid phase, Ba2YCuO5, and a liquid at 1266 K in air. Ba2YCu3O x crystals are formed around the primary crystals, BaY2CuO5, by a peritectic reaction on cooling from 1473 K in air.

High-temperature X-ray measurements were carried out on Bi-Sr-Ca-Cu-O. It was found that the 30 Å phase showed incongruent melting forming new crystalline phases which differed depending on the compositions. Crystallization from the melt by cooling first produced the 30 Å phase on solidification and then the 24 Å phase crystallized around 730°C. Crystallization from the glassy phase by heating started at 430°C and led to the 24 Å phase, which changed to the 30 Å phase above 800°C. As a rule, low-temperature crystallization from the amorphous phase takes place below 730°C to form the 24 Å phase in Bi-Sr-Ca-Cu-O.

We have developed a high-pressure cell for neutron scattering. The cell uses a barrel-shaped support cylinder made of sintered ceramics. Samples 6 mm in diameter and 10 mm long can be accommodated. The cell is suitable for use at low and high temperatures, after a pressure generated at room temperature is locked. The change of pressure on cooling to cryogenic temperatures is estimated by measuring the lattice parameter of NaCl. Besides the pressure locking technique, continuous pressurization can be achieved at room temperature by using a built-in mini-press while the cell is mounted on a goniometer of neutron spectrometer.