High fracture toughness, low thermal conductivity, and thermal expansion coefficient (TEC) matching substrate are essential for thermal barrier coatings (TBCs) and abradable seal coatings (ASCs). In this work, TmNbO₄/Tm₃NbO₇ composites are designed and synthesized to increase their fracture toughness (K_IC) and thermal insulation performance. Compared with those of TmNbO₄ (K_IC = 2.2±0.1 MPa·m^1/2) and Tm₃NbO₇ (K_IC = 1.7±0.2 MPa·m^1/2), the increments in fracture toughness are as high as 50.0% and 91.1%, respectively. The highest toughness reaches 3.3±0.4 MPa·m^1/2, which is attributed to the superior combination of grains between TmNbO₄ and Tm₃NbO₇, as well as the simultaneous effects of microcracks and crack bridging and bifurcation. Accurate estimation of the effect of the interfacial thermal resistance on the thermal conductivity at low temperatures was achieved using the minimum interfacial thermal resistance model. A novel method is proposed to inhibit radiative heat transfer by utilizing oxides with glass-like thermal conductivity to suppress thermal radiation. Consequently, the TmNbO₄/Tm₃NbO₇ composite maintains a low thermal conductivity (1.19–2.02 W·m⁻¹·K⁻¹) at 1000 °C. The high TECs (10.4×10⁻⁶–11.8×10⁻⁶·K⁻¹ at 1500 °C) and excellent high-temperature stability ensure that the designed TmNbO₄/Tm₃NbO₇ composites can be used at temperatures reaching 1500 °C. Accordingly, simultaneous enhancement of fracture toughness and thermal insulation in TmNbO₄/Tm₃NbO₇ composites is effective, and the revealed mechanisms are useful for various materials.

In situ phase separation precipitates play an important role in enhancing the thermoelectric properties of copper sulfides by suppressing phonon transmission. In this study, Cu_1.8S composites were fabricated by melting reactions and spark plasma sintering. The complex structures, namely, micron-PbS, Sb₂S₃, nano-FeS, and multiscale pores, originate from the introduction of FePb₄Sb₆S₁₄ into the Cu_1.8S matrix. Using effective element (Fe) doping and multiscale precipitates, the Cu_1.8S+0.5 wt% FePb₄Sb₆S₁₄ bulk composite reached a high dimensionless figure of merit (ZT) value of 1.1 at 773 K. Furthermore, the modulus obtained for this sample was approximately 40.27 GPa, which was higher than that of the pristine sample. This study provides a novel strategy for realizing heterovalent doping while forming various precipitates via in situ phase separation by natural minerals, which has been proven to be effective in improving the thermoelectric and mechanical performance of copper sulfides and is worth promoting in other thermoelectric systems.

Four high-entropy perovskite (HEP) RETa₃O₉ samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications. The prepared samples maintained low thermal conductivity (1.50 W·m^-1·K^-1), high hardness (10 GPa), and an appropriate Young’s modulus (180 GPa), while the fracture toughness increased to 2.5 MPa·m^1/2. Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity. We analysed the influence of different parameters (the disorder parameters of the electronegativity, ionic radius, and atomic mass, as well as the tolerance factor) of A-site atoms on the thermal conductivity. Enhanced thermal expansion coefficients, combined with a high melting point and extraordinary phase stability, expanded the applications of the HEP RETa₃O₉. The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.

HfO₂ alloying effect has been applied to optimize thermal insulation performance of HoTaO₄ ceramics. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are employed to decide the crystal structure. Scanning electronic microscopy is utilized to detect the influence of HfO₂ alloying effect on microstructure. Current paper indicates that the same numbers of Ta⁵⁺ and Ho³⁺ ions of HoTaO₄ are substituted by Hf⁴⁺ cations, and it is defined as alloying effect. No crystal structural transition is introduced by HfO₂ alloying effect, and circular pores are produced in HoTaO₄. HfO₂ alloying effect is efficient in decreasing thermal conductivity of HoTaO₄ and it is contributed to the differences of ionic radius and atomic weight between Hf⁴⁺ ions and host cations (Ta⁵⁺ and Ho³⁺). The least experimental thermal conductivity is 0.8 W·K^-1·m^-1 at 900 ℃, which is detected in 6 and 9 mol%-HfO₂ HoTaO₄ ceramics. The results imply that HfO₂-HoTaO₄ ceramics are promising thermal barrier coatings (TBCs) due to their extraordinary thermal insulation performance.