Oxoeuropates of alkali metals

Full text: There are only few works on the study of M-Eu-O (M=Na-Cs) system. This is owing to extreme hygroscopicity and high volatility of alkali metal oxides used in the reaction with europium oxide. The use of other compounds such as nitrates and carbonates is undesirable because the chemical activity of these substances is not sufficient. Only data on the oxides with MEuO2 composition have been reported up till now. But the single-crystal X-ray diffraction was studied only for RbEuO2 . Reliable data on caesium oxoeuropates are not present. The use of alkali metal peroxide or superoxide in considerable abundance in the solid-state synthesis is a new and promising method for synthesis of transition metal sophisticated oxides with alkaline cations. This method allows us to get appropriate compounds in a short time with a good yield even at not-too-high temperatures. Heating Eu2O3 with Na-2O2, KO2 and CsO2 at about 500 deg C led to formation of yellow-green products. The reaction with caesium superoxide passed most intensively and was accompanied by high exothermal effect. The obtained substances differed in their X-ray powder diffraction parameters from the known ones. Absorption 151Eu Moessbauer spectra were single lines with the following parameters of isomer shift (δ) relative to Eu2O3 and the width at half height (Γ): δ=0.33±0.03 mm.s-1, Γ=2.53∫0.06 mm.s-1 for sodium europate; δ=0.16±0.03 mm.s-1, Γ=2.95±0.05 mm.s-1 for potassium one and δ=0.18±0.03 mm.s-1, Γ=2.92±0.09 mm.s-1 for caesium derivative. The synthesis of the compounds was lasting only a few seconds and no europium oxide was found in the products. However some heating had to be continued to crystallize the substance well. In this case the narrowing of the lines was seen in the Moessbauer spectra and X-ray patterns. The isomer shifts value prove that europium is trivalent in these compounds. Broadening of the Moessbauer lines for potassium and caesium europates is indicative of quadrupole interactions