X-ray structural studies of the superconducting La system

We have investigated the influence of the incorporation of Ca and Nd ions on the structural and superconducting properties of the system by Rietveld refinement of x-ray diffraction patterns of seven samples, i.e. , 0.10, 0.20, 0.30, 0.40, 0.50 and 0.60 together with a.c. susceptibility and oxygen content measurements. X-ray data confirm the occurrence of a single-phase tetragonal structure with a space group of for all the seven samples and all Nd ions exclusively occupy La sites. Ca substitutes onto the La sites with a concomitant displacement of La onto the Ba sites for and for ; most of the Ca, %, enters La sites with some fraction occupying Ba sites. Samples with are superconducting and is between 42 and 80 K. With increasing x = y, both the hole concentration in the -O layers and increase to a maximum value of 0.309 and 80 K respectively at . An approximate correlation between and the hole concentration is suggested.