THE CHEMICAL CONTROL OF HIGH-T(C) SUPERCONDUCTIVITY - METAL-SUPERCONDUCTOR-INSULATOR TRANSITION IN (TL1-YPBY)SR2(CA1-XYX)CU2O7

We have carried out a detailed study of the relationship between the semiconducting, the superconducting, and the metallic region in the system (Tl0.5Pb0.5)Sr2(Ca1-xYx)Cu2O7. The critical density (or concentration), nc, derived from Hall measurement of the titled series compounds at which the transition from insulator to metal place can be given by the well-known Mott formula: nc1/3aH*=0.26 where aH* is the effective Bohr orbit radius of the isolated donor or acceptor state wavefunction. We propose that the insulator-metal transition in the cuprates generally occurs at a very high hole density (nc∼1020-1021cm-3) as compared to conventional doped semiconductors (nc∼1017-1018cm-3) but rather lower than the critical densities for elemental metals (nc>1021cm-3). © 1993 The Minerals, Metals and Materials Society