Influence of Native Defects on the Structural, Electronic, Thermal, and Ionic Transport Properties of YBO _3 ± δ Perovskites

The development of cathode materials with high ionic conductivity and thermomechanical compatibility remains a major challenge for advancing solid oxide fuel cells (SOFCs), especially at intermediate operating temperatures. In this work, we present a comprehensive computational study of orthorhombic YBO_3±δ perovskites, where B = Sc, Ti, V, Cr, Mn, Fe, Co, or Ni, using a combined approach of density functional theory (DFT) and molecular dynamics (MD). We evaluate the influence of native defects, oxygen vacancies (V_O), and interstitial oxygen (O_i) on the structural, electronic, thermal, and ionic transport properties. Our results show that YCrO₃ and YTiO₃ exhibit thermal expansion coefficients (TECs) compatible with widely used electrolytes such as YSZ. Hybrid DFT calculations reveal that pristine compounds, except for YNiO₃, behave as moderate-to-wide bandgap semiconductors, with native defects generally reducing the bandgap. MD simulations indicate that pristine (Pr) materials show negligible oxygen ion mobility, while the presence of defects substantially enhances ionic conductivity. O_i defects are particularly effective, yielding lower activation energies and higher self-diffusion coefficients compared to V_O. These findings demonstrate the critical role of defect engineering and highlight the potential of combined MD and DFT methodologies for the analysis and design of SOFC cathodes.