First principles insights into solid solution mechanisms of doped Gd ₂ Zr ₂ O ₇ and guides to develop novel thermal barrier coating materials

Gd₂Zr₂O₇ (GZO)-based compounds are currently one of the most promising materials for thermal barrier coatings (TBCs), in which some dopants are introduced. The dopants induce change in GZO lattice and improve the properties, however, the underlying mechanisms related to solid solution modes of the dopant remain insufficiently understood. In this study, first-principles calculations was employed to investigate the solid solution mechanism of Yb and Sc co-doping in GZO. The results showed that both substitutional and interstitial doping coexist in the GZO lattice. At a Yb doping content of 12.5 at.%, a substitutional solid solution formed in the GZO lattice, and further introduction of Sc into the lattice, Sc atom occupied interstitial sites at concentrations below 5.88 at.%. The calculation results indicate that 11.76 at.% Yb and 5.88 at.% Sc co-doped GZO (GYbSc) exhibited the lowest thermal conductivity, the highest coefficient of thermal expansion (CTE), and relatively high toughness. Experimental results demonstrated that GYbSc exhibits high toughness (2.09 MPa·m^1/2). At 1200 °C, the coefficient of thermal expansion of GYbSc increased by 5% compared to GZO, and its thermal conductivity decreased by 37%, with values of 11.059 × 10^-6 K^-1 and 0.935 W·m^-1·K^-1, respectively. GYbSc also displayed outstanding CMAS corrosion resistance. This work not only explore a promising TBC material, but also provides a new perspective for clarifying the mechanisms for the improved properties of doped compounds and developing novel TBC materials.