STRUCTURAL STUDY OF A HOLLANDITE-TYPE KXIRO2

The new ternary oxide KxIrO2(x approximate to 0.25) was prepared by heating stoichiometric proportions of K2CO3 and pure, chlorine-free IrO2 at 1000 degrees C for 1 hr. The monoclinic cell of the phase corresponds to the following parameters: a = 10.0206(4) Angstrom, b = 3.15268(9) Angstrom, c = 10.0535(4) Angstrom, and beta = 90.113(3)degrees. The Rietveld atomic structure refinement made in the I2/m space group yielded a reliability factor of R(wp) = 17.0 and chi(2) = 1.19. The structure corresponds to a slight distortion of the well-known hollandite-type structure, with a mean Ir-O distance of 2.03 Angstrom, a value intermediary between that found for Ir(III) and Ir(IV), in agreement with partially reduced iridium in KxIrO2. (C) 1995 Academic Press, Inc.