COMPOSITION, CRYSTAL-STRUCTURE AND SUPERCONDUCTING PROPERTIES OF HG-BA-CU-O AND HG-BA-CA-CU-O SUPERCONDUCTORS

The composition, crystal structure and superconducting properties of H g-Ba-Cu-O and Hg-Ba-Ca-Cu-O superconductors were investigated. Samples with various nominal compositions were prepared from the mono-oxides of Hg, Ba, Ca and Cu using various sintering processes. The samples we re examined by X-ray powder diffraction and energy dispersive X-ray an alysis (EDX). The Hg-Ba-Cu-O samples were found to be nearly single ph ases of HgBa2CuO4+delta (Hg.1201), but the Hg-Ba-Ca-Cu-O samples conta ined HgBa2Ca2Cu3O8+delta, (Hg-1223), HgBa2CaCu2O6+delta (Hg-1212) and other phases. The fraction of the higher-T(c) phase in the Hg-Ba-Ca-Cu -O sample varied in accordance with the nominal composition. High-reso lution transmission electron microscopic (HRTEM) studies revealed the existence of Hg-1201 (tetragonal cell with a=3.85 and c=9.5 angstrom), Hg-1212 (c=12.6 angstrom), and Hg-1223 structures (c= 15.7 angstrom). Most of the Hg-Ba-Cu-O samples exhibited 95 K-class superconductivity , and the Hg-Ba-Ca-Cu-O samples showed 130 K-class superconductivity. The highest Meissner onset temperature, T(cm) determined from DC susce ptibility was 134 K. The same sample showed superconductivity with a a pproximately 16% diamagnetic volume fraction at 5 K.