Polymorphism and physical properties of pure and lead-doped monoclinic Sm2MoO6 oxymolybdates

Abstract

The Sm₂MoO₆ compounds, also known as oxymolybdates, were synthesized in air using a solid-phase method. A series of techniques were employed to characterize the undoped and, for the first time, lead-doped samples. It has been demonstrated that lead-containing samples form a wide range of solid solutions, which are isostructural (sp. gr. C2/c) to the pure monoclinic Sm₂MoO₆ compound. The thermal stability, polymorphism, and conductive properties of the obtained samples were studied in detail. Doping Sm₂MoO₆ ceramics with lead results in a notable increase in conductivity compared to the pure sample, with conductivity reaching 10⁻³ S cm⁻¹ at 900 °C. This improvement is due to the formation of oxygen vacancies through the heterovalent substitution of cation sublattice. In contrast to undoped samarium oxymolybdates, Pb-containing Sm₂MoO₆ ceramics demonstrate the capacity to transfer protons, resulting in an overall increase in conductivity in a wet environment.