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Magnetization is measured on several 315 V3Si single crystals. The magnetization curve of the purest sample, which is a high-a superconductor in the pure limit, is fairly reversible, accompanied by an upward curvature near H, 2 probably caused by the Pauli paramagnetic effect. Those of the other samples show the peak effect near H, 2, and a scaling law between the pinning force density Fp and the magnetic field holds. The magnetic induction B changes nonlinearly across the sample, and the sign of d B/dr changes at the field where Fp attains a maximum. The strain also shows the peak effect near H, z, corresponding closely to that of the pinning force.

Superconducting oxides of Tl2Ba2Ca n-1Cu n O2n+4 with n=1, 2 and 3 were synthesized, and their structure and chemical composition were examined by X-ray powder diffraction, EPMA, Rietveld analysis and electron microscopy. Partial substitution of Tl with Ca was confirmed, but the production of holes in Cu layers expected from this substitution was rather small for a 120 K superconductor. Charge transfer of Tl3-δ-Cu2+δ would provide both the hole in the Cu-O bond required for high T c and s-like electron of Tl atoms for stabilization of layered structures.

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