STRUCTURE AND THERMOCHEMICAL REACTIVITY OF CARUO3 AND SRRUO3

Single crystals of CaRuO3 (1) and SrRuO3 (2) have been synthesized by flux method and their structures have been determined by means of single crystal X-ray diffraction techniques. The crystallographic data are (1): formula weight fw = 189.15, orthorhombic, space group Pnma (No. 62), a = 5.524(1), b = 7.649(2), c = 5.354(1) A ̊, V = 226.2 A ̊3, Z = 4, Dx = 5.554 g cm-3, μ = 81.97 cm-1, final R = 0.031 for 297 observed reflections. (2): formula weight fw = 236.69, cubic, space group Pm3 (No. 200), a = b = c =3.910(1) A ̊, V = 59.8 A ̊3, Z = 1, Dx = 6.572 g cm-3, μ = 275.28 cm-1, final R = 0.032 for 33 observed reflections. The thermochemical reactivity of the two phases has been investigated as function of temperature and ambient atmosphere. In oxidizing or inert gas atmospheres both compounds prove to be stable up to 1200 K. In reducing atmospheres such as molecular hydrogen, however, elementary ruthenium and the corresponding earth alkali metal oxides are obtained as microcrystalline mixtures at relatively low temperatures. The mechanisms of the reductions prove to be different. © 1990.