SrTa₂O₆: A new thermal barrier coating material with amorphous-like thermal conductivity and ultra-low oxygen-ion conductivity

In the pursuit of low thermal conductivity is an enduring challenge that driving research in thermal barrier coating (TBC) materials. It has become a general consensus that thermal conductivity can be reduced by enhancing compositional complexity and introducing microstructural defects. However, these approaches inevitably increase the technological complexity to synthesize materials and degrades the oxygen barrier capability of the coatings. Therefore, synergistically optimizing the thermal conductivity and oxygen resistance of TBC materials remains a critical issue. Herein, a TBC candidate material SrTa₂O₆ with amorphous-like thermal conductivity and ultra-low oxygen-ion conductivity is presented. The phase composition, microstructure, mechanical and thermal properties, and oxygen barrier capability of SrTa₂O₆ were investigated comprehensively. Notably, the Young's modulus, shear modulus and bulk modulus of SrTa₂O₆ is 207, 86, and 115 GPa respectively, which is similar to those of yttria-stabilized zirconia (YSZ). The Vickers hardness is comparable to YSZ at 8.9 ± 0.1 GPa. The coefficient of thermal expansion (CTE) of SrTa₂O₆ is 10.8 × 10⁻⁶/K at 1200 ℃, which is close to that of YSZ. Attributed to the strong intrinsic phonon-phonon scattering arising from the oxygen vacancies introduced by nonstoichiometric ratios of Sr²⁺ and Ta⁵⁺, and the large difference in the interatomic bonding between Sr-O and Ta-O, SrTa₂O₆ exhibits amorphous-like thermal conductivity characteristics with the increment of temperature. The thermal conductivity of SrTa₂O₆ ranges from 1.69 to 2.12 W·m⁻¹·K⁻¹ at 25–900 ℃, which is lower than most known thermal barrier materials, such as YSZ and rare earth tantalate. Moreover, SrTa₂O₆ exhibits ultra-low oxygen-ion conductivity of 2.07 × 10⁻⁵ S·cm⁻¹ at 900 ℃, which is three orders of magnitude lower than that of the state of art TBC material 8YSZ (3.47 ×10⁻² S·cm⁻¹). This work not only proves the application aspect of SrTa₂O₆ for TBC material, but also points out an avenue to balance the thermal conductivity and oxygen barrier ability of TBCs.