Neutron powder diffraction study of two sodium platinum oxides: Nasub(1.0)Pt3O4 and Nasub(0.73)Pt3O4

Neutron powder diffraction profile analysis has been used to confirm the structures of Nasub(1.0)Pt3O4 and Nasub(0.73)Pt3O4. Both compositions are cubic in space group Pm3n with Z = 2. The structure of Nasub(1.0)Pt3O4, with a = 5.6868(2) A as determined by X-ray powder diffraction, was refined to a final discrepancy factor for the weighted profile of Rsub(wP) = 0.120 for 30 peaks representing 39 reflections. The structure of Nasub(0.73)Pt3O4, a poorly crystallized compound with a = 5.675(1) A, was refined to Rsub(wP) = 0.212 for 31 peaks representing 40 reflections. Reliable thermal parameters were determined for lighter atoms in this platinum-dominated structure. The refined values of the sodium occupancy factor in both cases confirm the chemical analysis. Sodium occupancy values are also consistent with the linear relationship of unit-cell measurements vs sodium content for these compounds. The short Pt-Pt distance of 2.843 A in the structure of Nasub(1.0)Pt3O4 is consistent with its electrical properties. The metallic resistivity of Nasub(1.0)Pt3O4 (rho = 9 x 10-7 Ωm at 293 K) and the presence of a single Pt site with formal valence 7/3 places Nasub(x)Pt3O4 compositions in class III-B of the Robin and Day mixed-valence classification [Robin and Day (1967). Adv. Inorg. Chem. Radiochem. 10, 247-422]. (Auth.)