SUPERCONDUCTING TRANSITION-TEMPERATURE IN MERCURY HTSC-CUPRATES UNDERHYDROSTATIC-PRESSURE

A study is made of the properties of the homologous series of mercury HTSC-cuprates HgBa2Can-1CunO2n+2+delta with n=1-8. Experiments are con ducted under pressure for samples with n=1-5. The Hg-1223 and Hg-1234 phases were synthesized using a controlled high pressure chamber. The oxygen content of an initial mixture corresponding to the Hg-1234 phas e was varied by changing the composition of the initial BaO/BaO2 oxide s. The dependence of the superconducting transition temperature T-c on the lattice constant a (and, therefore, on the oxygen content) and of T-c(max) and dT(c)(max)/dp on n are convex upward up to n=4, 5. The m aximum values always correspond to the Hg-1223 phase. Experimental T-c (max)(n) curves for the phases with n=1-6 and dT(c)(max)/dp curves for n=1-5 are compared with Anderson's theory (the so-called RVB model). A general analysis of these results indicates that the mercury cuprate s have an ideal structure for HTSC. The Hg-1223 phase is the ''champio n'' in this ideal structure and the critical temperature corresponding to this phase (T-c= 135 K) is the highest at atmospheric pressure. (C ) 1998 American Institute of Physics.