Mechanism of Conductivity in the Rare Earth Layered Ln<sub>2</sub>MoO<sub>6</sub> (Ln = La, Pr, and Nd) Oxymolybdates: Theoretical and Experimental Investigations
Ekaterina Orlova, Yelizaveta A. Morkhova, Anastasia V. Egorova, E. P. Kharitonova, Н. В. Лысков, В. И. Воронкова, Artem A. Kabanov, А. А. Велигжанин, Natalia A. Kabanova
Abstract
Electrical transport in polycrystalline rare earth oxymolybdates Ln2MoO6 (Ln = La, Pr, and Nd) was investigated using theoretical and experimental methods. The theoretical approach consisted of geometrical–topological analysis, bond valence site energy (BVSE) simulation, and density functional theory (DFT) calculations. The BVSE modeling revealed that ionic conductivity can occur only by oxygen migration. The DFT calculations showed the roughly equal value of the energy barriers to oxygen migration in all oxymolybdates (less than 0.85 eV). The oxygen pressure-dependent isotherms of Ln2MoO6 (Ln = La, Pr, and Nd) at 1 × 10–18─0.21 atm show a mixed ionic and electronic conductivity mechanism in the temperature range of 700–900 °C. The total conductivity reached 10–5 S/cm at 800 °C for La2MoO6 and Nd2MoO6 and 10–3 S/cm at 800 °C for Pr2MoO6. All three layered oxymolybdates Ln2MoO6 (Ln = La, Pr, and Nd) exhibit proton conductivity in a humid atmosphere.