Structural and compositional investigations of Zr4Pt2O: A filled-cubic Ti2Ni-type phase

Syntheses, structural and compositional analyses of the filled cubic Ti₂Ni-type phase in Zr-Pt-O system have been studied, largely for the platinum-richer compositions. Diffraction quality crystals were grown by annealing an arc-melted composition Zr₄Pt₂O_0.66 at 1600 °C under Ar. The refined composition Zr_4.0Pt_1.95(1)O_0.93(6) (a=12.5063(6) Å, , Z=16) is close to the idealized composition Zr₄Pt₂O known in several other Zr-T-O systems (T=late 4d or 5d transition element). (This composition has been erroneously reported by ICDD for years as Zr₆Pt₃O (No. 00-017-0557) and referred to as ε-Zr₆Pt₃O.) The product is only marginally poor in platinum and oxygen, in contrast to the 1960 reports of metallographic studies (∼Zr₄Pt_1.62O_0.44). Under arc-melting conditions, high yields of the cubic phase are obtained from samples with lower platinum concentrations (Zr₄Pt_1.74O_1.04), whereas samples near the refined cubic composition contain hexagonal Zr₅Pt₃O_x as well (Mn₅Si₃-type). The hexagonal structure of binary Zr₅Pt₃ was also refined (Mn₅Si₃ type, P6₃/mcm, a=8.210(1) Å, c=5.385(2) Å) and shown to be non-stoichiometric to at least Zr₅Pt_2.5.