High oxygen pressures and the stabilization of the highest oxidation states of transition elements

The stabilization of the highest oxidation states n+ of transition elements Mn+ is an important way of evaluating the role of the covalency of the (Mn+-O) bond in the physico-chemical properties of corresponding oxygen lattices. Recently, using high oxygen pressures, Ir(VI) has been stabilized in A(2)BIr(VI)O-6 oxides with the perovskite-type structure (A = La,Ba,Sr; B = Ca,Sr,Mg,Zn,Li). Through XRD and XANES analyses, the Mn+-O distance and the splitting energy between t(2g) and e(g) levels at the Ir(VI) site have been evaluated. The magnetic properties of such ordered A(2)BIr(n+)O(6) perovskites (n = IV,V,VI) have been discussed as a function of the covalency of the Irn+-O bond and the Irn+-O distance. (C) 1997 Elsevier Science S.A.