Insights into the electronic, mechanical and thermodynamic properties of pyrochlore oxides A2B2O7: A first-principles study

Abstract

Pyrochlore compounds (A₂B₂O₇) have garnered significant importance in materials research due to their distinctive structural, electronic, and thermal properties, making them promising candidates for advanced applications. This study explores the potential of pyrochlore oxides—Nb₂Sn₂O₇, Pr₂Hf₂O₇, Sc₂Hf₂O₇, and Sc₂V₂O₇, through Full Potential Density Functional Theory (FP-DFT), examining their structural, electronic, elastic, and thermodynamic characteristics. The calculated results demonstrate that these compounds possess notable elastic, mechanical, and thermodynamic stability. Among them, Nb₂Sn₂O₇, Pr₂Hf₂O₇, and Sc₂V₂O₇ exhibit metallic behaviors with zero band gaps, whereas Sc₂Hf₂O₇ features an indirect band gap of 1.568 eV, primarily influenced by O-p states. The analysis of elastic and mechanical properties highlights their stable yet anisotropic nature, with a notable tendency towards brittleness. Thermodynamic properties including thermal expansion coefficients, Gibbs free energy, Debye temperature, and specific heat capacity over a temperature range of 200–2000 K were also evaluated using quasi-harmonic Debye approximation. The low thermal conductivity, high thermal expansion comparable to yttria-stabilized zirconia (YSZ) topcoats, and favorable mechanical properties make these compounds ideal candidates for top layers in thermal barrier coatings.