The composition, crystal structure and superconducting properties of HgBaCuO and HgBaCaCuO 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 were examined by X-ray powder diffraction and energy dispersive X-ray analysis (EDX). The HgBaCuO samples were found to be nearly single phases of HgBa2CuO4+δ (Hg-1201), but the HgBa CaCuO samples contained HgBa2Ca2Cu3O8+δ (Hg-1223), HgBa2CaCu2O6+δ (Hg-1212) and other phases. The fraction of the higher-Tc phase in the HgBaCaCuO sample varied in accordance with the nominal composition. High-resolution transmission electron microscopic (HRTEM) studies revealed the existence of Hg-1201 (tetragonal cell with a=3.85 and c=9.5 A ̊), Hg-1212 (c=12.6 A ̊). and Hg-1223 structures (c=15.7 A ̊). Most of the HgBaCuO samples exhibit 95 K-classs superconductivity, and the Hg BaCaCuO samples showed 130 K-class superconductivity. The highest Meissner onset temperature, Tcm determined from DC susceptibility was 134 K. The same sample showed superconductivity with a ≈ 16% diamagnetic volume fraction at 5 K.
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