Powder neutron diffraction study of the structural phase diagram of the Ba(sub 1-x)K(sub x)BiO3 system

In this article we present a brief report of recent work carried out to elucidate the phase diagram of the Ba(sub 1-x)K(sub x)BiO(sub 3) system. A full account of this investigation will be published shortly. The recently discovered high-T(sub c) superconductor Ba(sub 1-x)K(sub x)BiO(sub 3) is unique in the sense that unlike the other high-T(sub c) superconductors, it does not contain CuO(sub 2) planes and is cubic rather than layered in structure. It does, however, exhibit a series of structural phase transitions as a function of both K concentration x and temperature. Superconductivity occurs only in a cubic phase and disappears abruptly at x (le) 0.4 where the behavior apparently becomes non-metallic. Few details have been available hitherto of the structural phases found as x is decreased, and some of the reported results are not consistent with each other. The present measurements were carried out on the H4S triple axis spectrometer at Brookhaven's High Flux Reactor and on the Special Environment Powder Diffractometer (SEPD) at Argonne's Intense Pulsed Neutron Source.