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/~.

Synthesis and crystal structure of the palladium oxides NaPd3O4, Na2PdO3 and K3Pd2O4

“…The refinement of the Na site occupation factor provided a value of 1.03(1) and confirmed thereby full occupation of this position. No improvement was achieved by symmetry lowering from Pm3n to P43n, that resulted in a shift of the O-position from (1/4,1/4,1/4) to (x,x,x) (as in Li 0.64 Pt 3 O 4 [16]). The deviation from x ¼ 1/4 was negligible.…”

X-ray absorption studies of some platinum oxides

“…The structure of Li0.6Pt3O4 has recently been determined. 8 The Pt2+ atoms are surrounded in a square-planar configuration by four oxygen atoms at 2.00 A. Cahen and Ibers9 have found Adams' catalyst to be a combination of Pt, a-Pt02, and NaxPt304.…”

Investigation of (Sr4−δCaδ)PtO6 using X-ray Rietveld refinement

“…The structure and crystal chemistry of a large number of Pt-containing phases have been reviewed by Schwartz and co-workers (Schwartz et al, 1982(Schwartz et al, , 1983Schwartz and Prewitt, 1984). In general the Pt-containing oxide compounds contain either Pt in fourfold planar coordination or Pt in sixfold octahedral coordination, such as in the compounds of M 2 Pt0 3 or M 4 Pt0 6 .…”