Mutual oxidation states of uranium and molybdenum in UMoO ternary oxides

Abstract

UMoO 6, UMoO 5, U 2MoO 8 and UMo 2O 8 have been prepared and identified by powder X-ray diffraction analysis. Mutual oxidation states of uranium and molybdenum in these ternary mixed oxides were determined by X-ray photoelectron spectroscopy (XPS), magnetic susceptibility measurement and electron spin resonance (ESR) absorption. All of the magnetic susceptibility vs. temperature curves for the oxides, except for UMoO 6, have broad peaks around 50 K, suggesting a magnetic exchange interaction between paramagnetic ions through oxygen atoms. For UMo 2O 8, an ESR signal with g = 1.94 and a linewidth of 0.0057 T was observed with a small anisotropy. This signal is attributed to pentavalent molybdenum. From the XPS spectra, the oxidation states of uranium and molybdenum in U 2MoO 8 are found to be pentavalent and hexavalent respectively. However, in UMo 2O 8 both uranium and molybdenum are in mixed pentavalent and hexavalent states. In UMoO 5, uranium is hexavalent with a shoulder corresponding to the pentavalent state, whereas molybdenum is pentavalent with a shoulder corresponding to the tetravalent state. In UMoO 6, both uranium and molybdenum show the hexavalent state, as seen from the chemical formula. Alternations of oxidation states between uranium and molybdenum, according to the kind of ternary mixed oxides, were observed.