Although rare earth zirconates (RE₂Zr₂O₇) are garnering attention as viable candidates for thermal barrier coatings (TBCs), they suffer from low fracture toughness and accelerated calcium–magnesium–alumina–silicate (CMAS) melt corrosion at higher service temperatures, which impede their practical applications. In this work, we developed a series of REAlO₃/RE₂Zr₂O₇ (RE=La, Nd, Sm, Eu, Gd, and Dy) composites with a eutectic composition that not only show a significant enhancement in fracture toughness, over a 40% increase relative to RE₂Zr₂O₇, but also exhibit improved resistance to CMAS corrosion. The enhancement of toughness arises from multiple mechanisms such as ferroelastic toughening, fine-grain strengthening, and residual stress toughening, all of which trigger more crack defections and energy consumption. Additionally, the CMAS penetration depth of REAlO₃/RE₂Zr₂O₇ composites is approximately 36% lower than that of RE₂Zr₂O₇. Al-O constituents in composites can capture CaO, SiO₂, and MgO in CMAS melt and increase its viscosity, resulting in the enhanced CMAS corrosion resistance. The thermophysical properties of the REAlO₃/RE₂Zr₂O₇ composites were also investigated, and their coefficient of thermal expansion and thermal conductivity are comparable to YSZ, indicating the potential as TBC materials.

Chemical doping is a normal strategy to tune thermal expansion coefficient (TEC) of ceramics in engineering applications, but the resultant TEC values usually follow Vegard’s law, as doping does not modify the nature of chemical bonding in ceramics and its anharmonicity. In this paper, we report abnormal TEC behavior in (Nd_1−xDy_x)₂Zr₂O₇ ceramics, where the TEC values remarkably exceed the values predicted by Vegard’s law and even exceed the values obtained for two constituents Nd₂Zr₂O₇ and Dy₂Zr₂O₇. In addition to a reduction in lattice energy with an increasing molar fraction of Dy (x) value, we attribute the additional increase in the TEC to the high concentration of Dy dopants in a pyrochlore (P) region, which can soften low-lying optical phonon modes and induce strongly avoided crossing with acoustic phonon branches and enhanced anharmonicity. We believe that this finding can provide a new route to break through the restriction imposed by the conventional Vegard’s law on the TEC values and bring new opportunities for thermal barrier coatings (TBCs) or ceramic/metal composites towards realizing minimized thermal mismatch and prolonged service life during thermal cycling.

Yttria-stabilized zirconia (YSZ) has been used as a thermal barrier coating (TBC) material in gas turbines for several decades. Although continuous efforts have been made to develop novel TBC materials that can work at a higher temperature, no single material other than YSZ has all the desired attributes for the TBCs. In this paper, we report the in-situ synthesis of quasi-binary GdNbO₄/Gd₃NbO₇ composites based on the simple Gd₂O₃–Nb₂O₅ binary phase diagram. The fracture toughness of these quasi-binary composites is remarkably enhanced compared with the value predicted by the rule of mixtures because the ferroelastic domain switching is more activated due to the residual stress in the quasi-binary composites, which triggers more crack defections due to the enlarged process zone. Additionally, the Gd₃NbO₇ phase provides a low thermal conductivity due to the substantial chemical inhomogeneity, which diffuses phonons. Gd₃NbO₇/GdNbO₄ exhibits a balanced thermal conductivity of 1.6 W/(m·K) at 1073 K and a toughness value of 2.76 MPa·m^0.5, and these values are among the best comprehensive properties that have been obtained for new TBC materials. The work demonstrates a feasible approach of designing a new TBC material with balanced properties and can be easily fabricated.

Graphene with excellent comprehensive properties has been considered as a promising filler to reinforce ceramics. While numerous studies have been devoted to the improvement of mechanical and electrical properties, incorporating graphene to ceramics also offers new opportunities for endowing ceramics with versatility. In this review, the recent development of graphene/ceramic bulk composites is summarized with the focus on the construction of well-designed architecture and the realization of multifunctional applications. The processing technologies of the composites are systematically summarized towards homogeneous dispersion and even ordered orientation of graphene sheets in the ceramic matrix. The improvement of composites in mechanical, electrical, electromagnetic, and thermal performances is discussed. The novel multifunctional applications brought by smart integration of graphene in ceramics are also addressed, including microwave absorption, electromagnetic interference shielding, ballistic armors, self-monitor damage sensors, and energy storage and conversion.