Analysis of structural distortions in non-stoichiometric ternary platinum oxides: Li0.64Pt3O4 and Co0.37Na0.14Pt3O4

Abstract

The structures of Li0.64Pt30 4 and Co0.37Na0.14Pt30 4 have been determined from neutron powder diffraction experiments and found to exhibit two kinds of internal structural distortions distinguishing them from the prototype NaPt304 structure in which the Na counterion occupies eight-coordinated cubic sites in the PtO 4 framework. Both the Li0.64Pt30 4 and Co0.37Na0.14Pt30 4 structures were characterized by modifications to the geometry of the eight-coordinated counterion site. In Li0.64Pt30 4 the Li ions were randomly distributed on these sites, and the oxygen coordination was no longer cubic, with four short Li-O distances of 2.22/k and four long ones of 2.65 A in the configuration of two interpenetrating tetrahedra. In Co0.37Na0.14Pt304 there was ordering of Co, Na, and vacancies in the eight-coordinated sites, which imposed a structural limit on substitution of eight-coordinated atoms to 0.5 per formula unit. In this case, cationoxygen coordination was cubic, with eight O atoms at a distance of 2.36 (1)A from the occupied counterion site. The Li0.64Pt30 4 structure, with a = 5.6242 (2)A and Z = 2, was refined in space group P43n by the Rietveld profile technique with a final weighted profile discrepancy factor Rwe = 0.160 for 35 reflections collected at 2 = 1.343/1,. The Co0.37Na0.14Pt30 4 structure, with a = 5.6321 (4)/i, and Z = 2, was refined in space group Pm3 using integrated intensities with a final weighted R w = 0.036 for 15 observations representing 22 reflections collected at 2 = 2.460/~.