Synthesis, structural characterization, and conductive properties of lanthanum-yttrium molybdate, a novel fluorite-like Nd5Mo3O16+δ-type material

Abstract

A series of samples with the general composition La<inf>5-x</inf>Y<inf>x</inf>Mo<inf>3-y</inf>O<inf>16.5-3y</inf> (0 ≤ x ≤ 5, 0 ≤ y ≤ 0.5) was obtained through solid-state reactions of metal oxides in the La<inf>2</inf>O<inf>3</inf> – Y<inf>2</inf>O<inf>3</inf> – MoO<inf>3</inf> system. Within the studied compositional range, the formation of a new lanthanum-yttrium molybdate, La<inf>5-x</inf>Y<inf>x</inf>Mo<inf>3-y</inf>O<inf>16.5-3y</inf>, was observed. This compound is isostructural to Nd<inf>5</inf>Mo<inf>3</inf>O<inf>16+δ</inf> (space group Pn3‾n) and exhibits a narrow homogeneity range. Rietveld refinement of X-ray diffraction data revealed that yttrium atoms predominantly occupy the 12e crystallographic site in the structure. Dense ceramic samples were prepared using the sol-gel method and were employed to investigate the electro-physical properties of the new phase. The exceptionally high dielectric permittivity observed at elevated temperatures is likely attributed to the mobility of oxygen ions within the crystal structure. The grain bulk conductivity follows a thermally activated behavior with a bend at ∼600 °C, reaching values of up to 10−2 S/cm at 900 °C.