Study of microstructure, electronic structure and thermal properties of Al2O3-doped tetragonal YSZ coatings

Highlights: • Al₂O₃-doped tetragonal YSZ coatings were prepared by plasma spraying. • Microstructures, electronic structures and thermal properties were investigated. • The effect of doping on structures and thermal properties of coatings was studies. Al₂O₃-doped tetragonal yttria-stabilized zirconia (t-YSZ) coatings were prepared by plasma spraying under various spraying parameters. The analysis of variance reveals that only Al₂O₃ addition significantly affects thermal properties of coatings. The electronic structures and microstructures results show that the increase in number of defects and boundary density with the increasing addition of Al₂O₃ enhances phonon scattering resulting in a decrease in the thermal conductivity, which suggests that the Al₂O₃ addition can improve the insulation performance of the YSZ coating. The increase in boundary density with the increase in Al₂O₃ addition is due to recrystallization resulting from the decreasing melting point of Al₂O₃–YSZ composites, lattice distortion, and the presence of amorphous structure and monoclinic Al₂O₃ pinning at grain boundaries. The change in the coefficient of thermal expansion with Al₂O₃ addition is attributable to the variation in the bonding strength of the Al₂O₃-doped t-YSZ caused by the change in lattice constants.