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Y3NbO7 is regarded as a prospective material for utilization in thermal barrier coating applications, given its low thermal conductivity, high thermal expansion coefficients (TECs), and low oxygen ion conductivity. This study focuses on the dominant mechanisms of thermal properties of Y3-xAxNbO7 (A = Ca, In, Mg, Al; x = 0.05, 0.1) through the introduction of different types of cations. The oxygen ion conductivity of Y3-xAxNbO7 is as low as 2.16 × 10−5 S·cm−1 at 900 °C, which is dominated by contents of oxygen vacancies and electronegativity disorder. Three factors can contribute to reduction in thermal conductivity, including the phonon scattering caused by point defects, disorders in at. wt., ionic radius, and electronegativity, as well as atomic displacement parameters (ADPs). A comparison of the correlation between lattice point defects and thermal conductivity reveals that they are not the primary factor contributing to reduction in thermal conductivity. Conversely, doping elements with larger ADPs have been shown to significantly enhance the intensity of an-harmonic vibrations, thereby increasing TECs to 11.93 × 10−6 K−1 at 1400 °C and reducing thermal conductivity to 1.25 W m−1 K−1 at 25 °C. The effects of ADPs on reducing thermal conductivity overweigh that of lattice point defects in Y3NbO7 ceramics, and both TECs and thermal conductivity are optimized at the same time. This work proposes that large atomic displacements can act as a means of reducing thermal conductivity and increasing TECs for various ceramics. [ABSTRACT FROM AUTHOR]

Ceramic thermal barrier coatings (TBCs) with high toughness and low thermal conductivity are important for developing aero engines with high thrust‐to‐weight ratio and thermal efficiency. In this work, the properties of tantalate Y1/6Yb5/6TaO4 (YYT) were optimized by introducing 8 wt.% yttria‐stabilized zirconia (8YSZ), synthesized using spark plasma sintering, as a second‐phase ceramic. The highest toughness (3.57 MPa m1/2) of the YYT/8YSZ composite ceramics was due to multiple toughening mechanisms. The underlying mechanisms of these processes were revealed based on the microstructures and residual stress of the YYT/8YSZ composite ceramics. A shift from an intergranular fracture to a transgranular fracture was caused by the difference between soft‐grain YYT and hard‐grain 8YSZ, which consumed the fracture energy. Furthermore, the formation of microcracks, crack deflection, bridging, and branching were analyzed based on the differences in Young's moduli and thermal expansion coefficients of YYT and 8YSZ. Internal defects and weak connections between the YYT and 8YSZ grains reduced the thermal conductivity of the composites until it reached its lowest value at 1.4 W m−1 K−1. The studied toughening mechanisms could be applied to various composites. Moreover, herein, we provide a new strategy to design and synthesize TBCs with enhanced performance. [ABSTRACT FROM AUTHOR]

This perspective outlines the research directions of ferroelastic rare‐earth (RE) tantalates (RETaO4), which have been studied as multifunctional thermal/environmental barrier coatings (T/EBCs) with working temperatures above 1600°C. Ferroelastic RETaO4 ceramics exhibit several distinct features, including the reversible second‐order ferroelastic phase transition, high toughness, low thermal conductivity, low oxygen ion conductivity, and adjustable thermal expansion coefficients. This perspective provides a concise summary of the research progress on tantalate coatings synthesized via air plasma spraying and electron beam physical vapor deposition. The service performance of tantalate coatings is typically evaluated through thermal fatigue and shock measurements. Uncovering the failure mechanisms and understanding influencing factors are key aspects for future studies. In this regard, establishing the synthesis‐structure‐property relationship of RETaO4 coatings is essential. This brief perspective can serve as a guide for future work on RETaO4 coatings and further advancements in their applications across various fields, including aviation engines and gas turbines. [ABSTRACT FROM AUTHOR]

A new family of ceramic environmental/thermal barrier coating (E/TBC) materials, that is, ATa2O6 (A = Co, Ni, Mg, Ca), for high‐temperature applications, are investigated and reported in this study. We focus on the synthesis and features of crystal structures, and on the mechanical and high‐temperature properties. ATa2O6 oxides have an extraordinary phase stability (up to 1300°C), and their thermal expansion coefficients (6.2–7.3 × 10−6 K−1) match those of SiC fiber‐enhanced SiC ceramic matrix composites (3–7 × 10−6 K−1). Their low thermal conductivities (min: 1.15 W·m−1·K−1) root in the slow phonon spreading speed and fierce phonon‐phonon scattering process, and they will provide exceptional thermal insulation. Moreover, their hardness (5.6–8.8 GPa), toughness (1.4–1.9 MPa·m1/2), and moduli (100–210 GPa) have good comparability with current E/TBCs. We propose the 33CaO‐9MgO‐13AlO1.5‐45SiO2 (CMAS) corrosion mechanisms of ATa2O6 ceramics, and their robust CMAS resistance relies on the phase stability of CaTa2O6 oxides. The excellent high‐temperature properties ensure that ATa2O6 can be used as E/TBCs to provide thermal insulation and CMAS corrosion protection. [ABSTRACT FROM AUTHOR]