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The reactivities of several oxide materials (OM) in direct contact with BSCCO powder has been tested at a temperature of approximately 845 • C in air. The OM such as BaZrO 3 , SrCO 3 , MgO and ZrO 2 showing little or no reactivity with BSCCO were mixed (10 wt%) with a BSCCO precursor powder and used for monocore tapes made by a standard powder-in-tube technique. The microstructure of the BSCCO+OM cores was analysed by SEM and XRD and the transport current properties-critical current, pinning force and resistance up to 16 T-were measured as a function of the magnetic field for various orientations with respect to the ab plane. The OM used influenced the electrical properties of the Bi-2223 phase in different ways. This is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212 → 2223 phase transformation as well as the Bi-2223 grain growth and grain connectivity. Submicrometre commercial SrCO 3 powder was evaluated as the best material from all those tested, for resistive barriers in Bi-2223/Ag tapes.

The magnetic-field dependence of the metal-to-insulator transition temperature, T c (B), in the quasi-onedimensional systems ͑Per͒ 2 M ͑mnt͒ 2 , with M ϭAu and Pt, was studied by magnetoresistance measurements under fields up to 18 T. In the Pt compound, our results show that T c (B) is anisotropic: T c (B) decreases as B 2 up to 18 T with a slope similar to that found in the Au compound when the magnetic field is applied parallel to the chain axis, while T c (B) decreases faster and does not follow a pure B 2 dependence when the magnetic field is applied perpendicular to the chain axis. This anisotropy of the field dependence denotes the coupling of the Peierls transition in the perylene chains to a spin-Peierls-like transition in the Pt͑mnt͒ 2 Ϫ chains, correlated with an anisotropic magnetic susceptibility, while in the Au compound a pure Peierls transition takes place. ͓S0163-1829͑96͒08445-7͔

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