Synthesis and properties of LnMoO4-type (Ln=La÷Lu, Y) molybdates

Synthesis of LnMoO4-type molybdates for the entire rare earths row was carried out in a vacuum furnace at 1400°C during 20 hours using Ln2MoO6 and MoO2. The obtained molybdates in the La÷Nd row crystallize in cubic syngony, europium molybdate EuMoO4 - in tetragonal syngony, LnMoO4 molybdates for Sm, Gd÷Lu, Y - in monoclinic symmetry. LnMoO4-type molybdates are stable up to 210-270°C. The main oxidation occurs at 600°C. Investigation of interaction processes between LnMoO4 and chlorine was carried out using a special-purpose set-up. Our results show that LnMoO4 interaction with chlorine occurs in 600-750°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°C. Interaction of LnMoO4 (Ln=La, Nd, Gd, Dy, Er) with sulphur was studied at 600 and 1000°C. The ratio LnMoO4: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 LnMoO4 with S up to 1000°C leads to the destruction of primary crystal structure of molybdates.