Oxygen-deficient perovskites

The oxygen deficiency of several ternary oxide systems with perovskite and perovskite-related structures has been investigated. Low temperature synthetic methods for the preparation of oxygen deficient perovskites were examined. Zirconium metal was used as a scavenger in closed systems to abstract stoichiometric amounts of oxygen from mixed metal oxides. The end members (x = 0.5) in the CaMnO{dollar}sb{lcub}rm 3-x{rcub}{dollar} and Ca{dollar}sb2{dollar}MnO{dollar}sb{lcub}rm 4-x{rcub}{dollar} systems can be prepared by this technique, though the thermally sensitive Ca{dollar}sb2{dollar}MnO{dollar}sb{lcub}3.5{rcub}{dollar} requires the use of temperature gradients. The synthesis of intermediates (0 {dollar}<{dollar} x {dollar}<{dollar} 0.5) in the CaMnO{dollar}sb{lcub}rm 3-x{rcub}{dollar} and Ca{dollar}sb2{dollar}MnO{dollar}sb{lcub}rm 4-x{rcub}{dollar} systems has also been studied, as well as the reduction of single crystals. An alternate approach to the synthesis of intermediate compositions through the reoxidation of reduced compounds was also explored.; A new oxygen deficient perovskite, LaSrCuAlO{dollar}sb5{dollar}, has been prepared. Single crystals, grown from a copper oxide flux, crystallize in an orthorhombic crystal system with the space group Pbcm. The unit cell dimensions (Z = 4) are a = 7.9219(6), b = 11.020(1), and c = 5.4235(4) A. The compound is a layered copper oxide with a structure related to that of the mineral brown millerite. Important structural features include buckled copper oxygen planes and aluminum-oxygen chains. Resistivity measurements show that LaSrCuAlO{dollar}sb5{dollar} is a semiconductor ({dollar}psb{lcub}rm 300K{rcub}{dollar} = 0.065 {dollar}Omega{dollar}-cm.) and magnetic susceptibility measurements demonstrate that the compound is paramagnetic down to 4K.; The reduction chemistry of CaRuO{dollar}sb3{dollar}, SrRuO{dollar}sb3{dollar}, BaRuO{dollar}sb3{dollar}, SrIrO{dollar}sb3{dollar}, and BaIrO{dollar}sb3{dollar} was examined. Samples were reduced at low temperatures ({dollar}leq{dollar}600{dollar}spcirc{dollar}C) by the oxygen getter method and by direct reduction with hydrogen gas. No evidence for oxygen deficient perovskites was observed. In almost all cases, the mixed metal oxide was reduced to form the zero valent platinum group metal and the binary oxide or hydroxide (AO or A(OH){dollar}sb2{dollar}). One exception was seen in the reduction of SrIrO{dollar}sb3{dollar} via the getter method where the intermediate Sr{dollar}sb4{dollar}IrO{dollar}sb6{dollar} was found.