Effects of doping Yb3+, La3+, Ti4+, Hf4+, Ce4+ cations on the mechanical properties, thermal conductivity, and electronic structures of Gd2Zr2O7

Abstract

The structural, mechanical, thermal, and electronic properties of a series of Gd-site and Zr-site substituted Gd2Zr2O7 pyrochlores have been investigated by first-principles calculations. Substitution of Gd3+ with smaller and heavier Yb3+ introduces strong phonon scattering effects and results in Gd1.5Yb0.5Zr2O7 exhibiting the lowest thermal conductivity. Substitution of Gd3+ with larger and lighter La3+ does not give as much reduction in the thermal conductivity as in Yb3+-doped Gd2Zr2O7. As for Ti4+, Hf4+ and Ce4+ substitution for Zr4+-site in Gd2Zr2O7, slight changes in thermo-physical properties are observed for Gd2Zr2-yTiyO7 and Gd2Zr2-yHfyO7 pyrochlores, while the substitution of Ce4+ for Zr4+ site results in significantly smaller Young's modulus, better ductility, smaller Debye temperature, and lower thermal conductivity. With the increasing Ce content, the Young's modulus subsequently decreases by 22.2–59.9 GPa. The thermal conductivity of Gd2Zr2O7 is significantly reduced by 21% with complete Ce doping at the Zr-site based on the Clarke's model. This is mainly caused by the fact that larger guest ions incorporation weakens the bonds and enhances the phonon scattering in the host oxides and thus effectively lowers the thermal conductivity. Considering the improved thermo-physical properties, the Gd2Zr2-yCeyO7 may be a more promising candidate of the next-generation topcoat materials for thermal barrier coatings than the pure Gd2Zr2O7. This study provides a theoretical perspective to design and select good thermally insulating materials at high temperatures.