Oxygen‐vacancy‐mediated microstructure and thermophysical properties in Zr 3 Ln 4 O 12 for high‐temperature applications

Yttria-stabilized zirconia (YSZ) has been considered as state-of-the-art material for high-temperature thermal barrier coatings, which provide thermal insulation to the superalloy components in gas turbines and jet engines. Oxygen vacancies induced by yttria substitutions are believed to be mainly responsible for the low thermal conductivity of YSZ due to their phonon scattering effect. However, high mobility of oxygen vacancies in YSZ leads to a rapid oxygen diffusion at high temperatures, therefore accelerates the failure of coatings by grain coarsening, sintering, and simultaneous oxidation of the underlying metallic bondcoat. In the present research, we further explored in the ZrO2-Ln(2)O(3) binary phase diagram and synthesized a series of ceramic materials with the chemical formula of Zr(3)Ln(4)O(12) (Ln=La, Gd, Y, Er, and Yb), in which more oxygen vacancies were involved and extremely low phonon thermal conductivities (1.3-1.6W/mK) were obtained, even approaching to the theoretical minimum. In addition, the mobility of these oxygen vacancies was remarkably suppressed by the lattice ordering with the decrease of Ln(3+) radius, as confirmed by X-ray diffraction, Raman and transmission electron microscopy. Thus, the oxygen barrier property and sintering resistance were significantly enhanced accordingly, which makes Zr(3)Ln(4)O(12) compounds promising thermal barrier coating materials for next generation gas turbines and jet engines.