Thermal stability of RuSr2GdCu2O8, Ru1 − xSr2GdCu2O8 − y, RuO2

Abstract Thermal stability of RuSr 2 GdCu 2 O 8 , Ru 0.9 Sr 2 GdCu 2 O 8 −  y , and RuO 2 powders in oxygen has been studied by thermogravimetry. Decomposition of RuSr 2 GdCu 2 O 8 and Ru 0.9 Sr 2 GdCu 2 O 8 −  y samples in 0.85 bar of oxygen appears as a solid phase process at ∼1050 °C. This is followed by peritectic decomposition with onset starting at ∼1110 °C for the stoichiometric sample and at ∼1090 °C for the Ru deficient one. We observed that sublimation of ruthenium oxide in 0.85 bar of oxygen starts at ∼850 °C and sample's humidity significantly increases a sublimation rate. Enhanced sublimation above 1060 °C was observed for powder mixtures (RuO 2  +  x CuO), x =0.1, 0.2, 0.5. Analysis of the sublimation process of these mixtures suggests existence of an unknown compound in Ru–Cu–O system with approximate composition Ru 1 −  x Cu x O 2 − y , x ⩽0.1. Various aspects of a synthetic route of rutenates and, in particular RuSr 2 GdCu 2 O 8 phase, eliminating Ru off-stoichiometry and phase separation, are discussed.