Thermal expansion coefficient of nonstoichiometric gadolinium zirconate: First-principles calculations and experimental study

A high thermal expansion coefficient (TEC) is highly desirable for a thermal barrier coating material to prolong the life of the entire coating system. The TECs of Gd_2-xZr_2+xO_7+0.5x (x = 0, ±0.125, ±0.25, ±0.375) have been studied by first-principles calculations and solid-state reactions. Due to the strong bond energy and interatomic interaction force between Zr and O, and Gd³⁺ having a higher thermal diffusion coefficient and lower solid solubility, the TEC of a material with higher Gd³⁺ content and lower Zr⁴⁺ content is improved. Calculated results show that the highest Gd³⁺ content (x = −0.375) increases the TEC of Gd_2-xZr_2+xO_7+0.5x from 7.26 × 10⁻⁶/K (x = 0.375) to 8.95 × 10⁻⁶/K (1500K). The Debye temperature decreases with increasing Gd³⁺ content. The experimental TEC is highest (11.593 × 10⁻⁶/K) at a content of x = −0.375, far exceeding that at x = 0.375 (10.690 × 10⁻⁶/K). The experimental results agree well with the calculated results. This work lays a foundation for obtaining rare-earth zirconate materials with outstanding thermal physical properties, and it provides a novel method for their creation.