ИСТИНА

Bi2O3-based solid solutions are interesting as promising oxygen conductors with conductivity reaching 0.1-1 S/cm at 800 °C. The pure Bi2O3 has a complex polymorphism. Four basic Bi2O3 phases are well known: 1) a-Bi2O3 monoclinic phase, stable at room temperature; 2) b-Bi2O3 tetragonal phase; 3) g-Bi2O3 cubic phase; 4) high-temperature d-Bi2O3 cubic phase with fluorite structure, which is stable in narrow temperature range 700-780 ºC and demonstrate extremely high oxygen conductivity near 3 S/cm. In order to stabilize the cubic oxygen-conducting d-Bi2O3 phase at room temperature, co-doping of Bi2O3 with two different impurities is simultaneously used. The purpose of this work is to study the phase formation, polymorphism, and properties of Bi2O3-based compounds in the ternary Bi2O3-Ln2O3-WO3 systems (Ln = La, Pr, Nd). Polycrystalline samples were obtained by solid state synthesis in air. Different phases with a cubic, tetragonal, monoclinic, and rhombohedral structure were observed in Bi2O3-Ln2O3-WO3 systems as the composition was changed. The high-temperature oxygen-conducting d-Bi2O3 phase with a cubic fluorite structure is stabilized in a narrow range of concentrations of 85-90 mol.% Bi2O3, which is much lower than in similar systems with molybdenum. Another stability field of compounds with the cubic fluorite structure (d1-Bi2O3 phase) was found in the Bi2O3-WO3-Nd2O3 ternary system near the Nd2WO6-NdBiO3 cut. Cubic d-Bi2O3 samples demonstrate high electrical conductivity, reaching 0.05-0.6 S/cm at 800 °C. It was found that the electrical conductivity increases with increasing bismuth concentration. In the low-temperature region, the electrical conductivity obeys the Arrhenius law with an activation energy close to 0.9 eV. Above 400 ° C, the conductivity can be approximated by the Vogel-Fulcher-Tamman law.