Ferroelastic ABO4 type RETaO4 and RENbO4 ceramics (where RE stands for rare earth) are being investigated as promising thermal barrier coatings (TBCs), and the mechanical properties of RETaO4 have been found to be better than those of RENbO4. In this work, B-site substitution of tantalum (Ta) is used to optimize the thermal and mechanical properties of EuNbO4 fabricated through a solid-state reaction (SSR). The crystal structure is clarified by means of X-ray diffraction (XRD) and Raman spectroscopy; and the surface microstructure is surveyed via scanning electronic microscope (SEM). The Young's modulus and the thermal expansion coefficient (TEC) of EuNbO4 are effectively increased; with respective maximum values of 169 GPa and 11.2×10–6 K–1 (at 1200 °C). The thermal conductivity is reduced to 1.52 W·K−1·m−1 (at 700 °C), and the thermal radiation resistance is improved. The relationship between the phonon thermal diffusivity and temperature was established in order to determine the intrinsic phonon thermal conductivity by eliminating the thermal radiation effects. The results indicate that the thermal and mechanical properties of EuNbO4 can be effectually optimized via the B-site substitution of Ta, and that
this proposed material can be applied as a high-temperature structural ceramic in future.