HIGH OXYGEN PRESSURES AND THE STABILIZATION OF THE HIGHEST OXIDATION-STATES OF TRANSITION-ELEMENTS

The stabilization of the highest oxidation states n+ of transition ele ments Mn+ is an important way of evaluating the role of the covalency of the (Mn+-O) bond in the physico-chemical properties of correspondin g oxygen lattices. Recently, using high oxygen pressures, Ir(VI) has b een stabilized in A(2)BIr(VI)O-6 oxides with the perovskite-type struc ture (A = La,Ba,Sr; B = Ca,Sr,Mg,Zn,Li). Through XRD and XANES analyse s, 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 d iscussed as a function of the covalency of the Irn+-O bond and the Irn +-O distance. (C) 1997 Elsevier Science S.A.