Extended investigation of the conductive characteristics of monoclinic tungstates with a Bi3.24Ln2W0.76O10.14 (Ln = La, Pr or Nd) composition

Abstract

δ-Bi₂O₃-based materials have long been a focus of interest as potential solid oxide fuel cell materials due to their high electrical conductivity. Here, extensive studies of thermal stability, polymorphism and conductivity have been carried out for the first time on Bi_3.24Ln₂W_0.76O_10.14 (Ln = La, Pr or Nd) compounds in the ternary Bi₂O₃–Ln₂O₃–WO₃ system, mentioned more than 20 years ago by Watanabe. The obtained single-phase materials were found to be sufficiently dense (more than 94%) and thermally stable (up to 900 °C). Emphasis was placed on studying the nature of the electrical transport of these phases, which was investigated through high-throughput calculations and experimental measurements. Theoretical studies included a crystal chemical evaluation of conductivity channels and migration energy, calculation of ionic conductivities using the kinetic Monte Carlo method, and determination of band gaps using a quantum-chemical approach. Experimental conductivity investigations were carried out over a wide temperature range (up to 900 °C) and at various oxygen partial pressures. For Bi_3.24Ln₂W_0.76O_10.14, the anionic type of conductivity is predominant with a share of the electronic component. The total conductivity values reached about 10⁻² S cm⁻¹ at 900 °C for all samples, confirmed by both calculation and measurement. These theoretical and experimental findings enhance the understanding of the nature and mechanism of Watanabe's phase conductivity.