Thermophysical properties of Yb3+-doped nonstoichiometric gadolinium zirconate ceramics

Low thermal conductivities and high thermal expansion coefficients are desirable for rare-earth zirconate thermal barrier coating materials. Introduction of cation doping and adjustment of the nonstoichiometry are efficient methods for enhancing the thermophysical characteristics of materials. Herein, the thermophysical properties of Yb 3+ -doped nonstoichiometric gadolinium zirconate ceramic materials were investigated using first-principles calculations and solid-state reaction techniques. As the Yb 3+ content increases, additional cations enter the interstitial spaces (for excess Gd 3+ gadolinium zirconate) and form vacancy defects (for excess Zr 4+ gadolinium zirconate), which serve as phonon scattering centres to decrease the thermal conductivity. When Yb 3+ is doped at the same concentration, gadolinium zirconate with excess Zr 4+ exhibits a lower thermal conductivity. Specifically, Gd 1.875 Yb 0.25 Zr 2.125 O 7 shows the lowest minimum thermal conductivity of 1.133 W/(m⸱K) (according to the Clark model) and 1.241 W/(m⸱K) (according to the Cahill model). In addition, the experimental results also suggest that the optimal content of Yb 3+ is 0.25 excess Zr 4+ gadolinium zirconate, which has the lowest intrinsic thermal conductivity of 1.037 W/(m⸱K) at 1300 K. Moreover, the thermal expansion coefficient of the Yb 3+ -doped excess Gd 3+ nonstoichiometric material is greater than that of the doped excess Zr 4+ material, this is due to the greater electronegativity difference between Yb 3+ and Zr 4+ than that between Yb 3+ and Gd 3+ and the lower binding energy of Gd-O than that of Zr-O. The experimental results and the calculated results are in good agreement. The aim of this work is to enhance the thermophysical characteristics of gadolinium zirconate ceramics for use as thermal barrier coating materials.