SYNTHESIS AND X-RAY-POWDER DIFFRACTION ANALYSIS OF THE HIGH-TC SUPERCONDUCTOR HGBA2CA2CU3O8Q-DELTA

The third member (Hg-1223) of the recently-discovered homologous serie s HgBa2Can-1CunO2n+2+delta, which having a T(c) of 118 K (assynthesize d sample) and 133 K (oxygen-annealed sample), was successfully prepare d by solid state reaction and short time annealing technique using the mixtures of metal oxides HgO, BaO, CaO and CuO with starting composit ion HgBa2Ca2Cu3Oy. We found that the combination of very short anneali ng time with optimum temperatures 715-725-degrees-C gives rise to a ve ry effective sintering of the constituents and avoids an excessive los s of Hg. This also means that the reaction should be followed by X-ray powder diffraction analysis of the material at each step. Sample so o btained displays a sharp superconducting transition determined both ma gnetically and resistively. The X-ray diffraction patterns of the 118 K phase and the 133 K phase both indicate a nearly single phase, corre sponding to the tetragonal structure of space group of P4/mmm and with lattice parameters a = 0.385 nm and c = 1.585 nm. Energy dispersive X -ray spectroscopic analysis (EDX) data of several flat grains of the H g-1223 sample shows that the cation stoichiometry is in agreement with the proposed chemical formulae.