Synthesis and properties of LnMoO(4)-type (Ln=La divided by Lu, Y) molybdates

Synthesis of LnMoO(4)-type molybdates for the entire rare earths row was carried out in a vacuum furnace at 1400 degrees C during 20 hours using Ln(2)MoO(6) and MoO2. The obtained molybdates in the La divided by Nd row crystallize in cubic syngony, europium molybdate EuMoO4 - in tetragonal syngony, LnMoO(4) molybdates for Sm, Gd divided by Lu, Y - in monoclinic symmetry. LnMoO(4)-type molybdates are stable up to 210-270 degrees C. The main oxidation occurs at 600 degrees C. Investigation of interaction processes between LnMoO(4) and chlorine was carried out using a special-purpose set-up. Our results show that LnMoO(4) interaction with chlorine occurs in 600-750 degrees C temperature range. The obtained rare earth oxochloromolybdates are close in their structure to that of gadolinium oxochlorotungstate GdWO4Cl, and crystallize in monoclinic syngony. The decomposition process of TR oxochloromolybdates begins at 600 degrees C. Interaction of LnMoO(4) (Ln=La, Nd, Gd, Dy, Er) with sulphur was studied at 600 and 1000 degrees C. The ratio LnMoO(4):S was 1:1. The specimen of GdMoO4+S composition is homogenous and has scheelite-type structure with unit cell parameters a=5.2023 Angstrom c=11.1960 Angstrom Increasing of quenching temperature for LnMoO(4) with S up to 1000 degrees C leads to the destruction of primary crystal structure of molybdates.