YBa₂Cu₃ O_7−δ samples stored in different environments have been studied over a period of 30 days employing TGA, electrical resistivity and X-ray diffraction measurements. Oxygen content andT_cdo not change significantly in samples stored in the normal laboratory environment, in a sealed tube or in a vacuum desiccator. Superconductivity is lost only in samples stored in a very humid atmosphere around 320 K.

Several new Na, Y and Zr substituted derivatives of Ca_0·5Ti₂(PO₄)₃ (CTP) have been synthesized. These derivatives retain the hexagonal structure of the parent (CTP) compound with minor changes in lattice parameters. Linear thermal expansion coefficients(α) have been obtained using a high sensitivity dilatometer.

BiO$_{0.75}$F$_{0.25}$BiS$_2$ crystallizes in tetragonal CeOBiS$_2$ structure (S. G. P4/nmm). We have investigated the effect of pressure on magnetization measurements. Our studies suggest improved superconducting properties in polycrystalline samples of BiO$_{0.75}$F$_{0.25}$BiS$_2$. The Tc in our sample is 5.3 K, at ambient pressure, which is marginal but definite enhancementover $T_c$ reported earlier ($=$5.1 K). The upper critical field Hc2(0) is greater than 3 T, which is higher than earlier report onthis material. As determined from the M–H curve, both H$_{c2}$ and H$_{c1}$ decrease under external pressure $P$ ($0 \leq P \leq 1$ GPa). We observe a decrease in critical current density and transition temperature on applying pressure in BiO$_{0.75}$F$_{0.25}$BiS$_2$.