Platinum Bronzes. IV. Preparation, Crystal Chemistry, and Physical Properties

The syntheses of several ternary platinum oxides are reported. The Na and Cd bronzes Na_xPt₃O₄ and Cd_xPt₃O₄ as well as the bronze-like CaPt₂O₄ were prepared in powder form under atmospheric pressure. The existence of Pt₃O₄ is discussed. Syntheses for Cd_xPt₃O₆ and a poorly defined new simple oxide of platinum with stoichiometry Pt₅O₆ are given. The stability of these various oxides is discussed and their lattice parameters are given. The crystal chemistry of these oxides is systematized using stability fields for the platinum bronzes and for A₃BX₄ compounds. The close structural relationship between the bronzes and Ag₃PO₄ and Ag₃AsO₄ is discussed. Photoelectron spectroscopic, magnetic susceptibility, and electrical conductivity data for the bronzes and various other platinum oxides are reported. From these data it is concluded that most bronzes are metallic oxides and a qualitative one-electron energy-band scheme is given explaining this metallic character. The nonexistence of CaPt₃O₄ is discussed in terms of both this scheme and thermodynamics. The tendency of the bronzes to incorporate large quantities of foreign cations is explained in terms of the cage-like bronze structure.