La1-xSrxCuO2.5 as a doped spin-ladder compound

The high-pressure synthesis, structural characterization, and physical properties of La1-xSrxCuO2.5 (0 less than or equal to x less than or equal to 0.20) are reported. The nondoped LaCuO2.5 prepared at high pressure of 6 GPa crystallizes in the CaMnO2.5 structure which is one of the prototypes of anion-deficient perovskites. The Rietveld analysis of the powder X-ray diffraction pattern remarkably shows a quasi-one-dimensional structure composed of Cu-O ladders. The magnetic susceptibility measurements suggest a spin liquid ground state with a large energy gap of 490 K as theoretically expected for a S = 1/2 Heisenberg antiferromagnetic ladder system. Systematic hole-doping is achieved by substituting Sr for La. A dramatic insulator-to-metal transition has been observed in the resistivity measurements on doping, but, with no signs of superconductivity as predicted theoretically for a lightly doped spin-ladder system. (C) 1996 Academic Press, Inc.