New fluorite-like lanthanum-europium molybdates with Nd5Mo3O16+δ-type structure

Abstract

Phase relations in the La2O3 – Eu2O3 – MoO3 ternary system were studied using polycrystalline samples obtained in air at 1250°C via solid-state reaction of metal oxides. The system contains a broad region of a cubic fluorite-like phase of lanthanum-europium molybdates, named LEMO, which is isostructural with Nd5Mo3O16+δ. However, the homogeneity range of this phase is quite limited and occurs at a lower MoO₃ content compared to neodymium molybdate. The citrate method was applied for the synthesis of LEMO ceramic samples with a relative density of 98 %. The crystal structure of La2.5Eu2.5Mo2.625O15.75 was analyzed by the Rietveld refinement using powder XRD data. The analysis revealed structural features of this europium-containing fluorite-like molybdate, specifically the splitting of oxygen atomic positions in the octahedral voids within the fluorite structure. The fluorite-like molybdate samples exhibited high electrical conductivity, with the grain bulk contribution at about 10−2 S/cm at 900°C, and intense red luminescence under near-UV and blue radiation.