The concept of high-entropy has recently emerged as a promising strategy in the development of advanced thermal barrier coating (TBC) materials. By introducing mass and size disorder through the incorporation of multiple distinct cations at a single crystallographic site in mixed oxides, high-entropy oxides (HEOs) can be designed to exhibit stabilized single-phase structures with intrinsically low thermal conductivities. In this work, we report the successful solid state synthesis and comprehensive characterization of three novel single-phase high-entropy perovskites: Ba(Ti1/5Zr1/5Hf1/5Sn1/5Mn1/5)O3, Ba(Ti1/5Zr1/5Hf1/5Sn1/5Ce1/5)O3, and Sr(Ti1/4Zr1/4Hf3/20Sn1/4Mn1/10)O3. The compounds Ba(Ti1/5Zr1/5Hf1/5Sn1/5Mn1/5)O3, Ba(Ti1/5Zr1/5Hf1/5Sn1/5Ce1/5)O3, and Sr(Ti1/4Zr1/4Hf3/20Sn1/4Mn1/10) exhibit the low thermal conductivities of approximately 1.84 Wm−1 K−1, 1.72 Wm−1 K−1, and 0.72 Wm−1 K−1, respectively, at 800 K. The Sr-based compound exhibits an ultra-low average thermal conductivity of ~ 0.63 W·m⁻1·K⁻1, which remains nearly constant over the temperature range of 300–800 K. This value corresponds to an almost 68% reduction compared to the benchmark thermal barrier coating (TBC) material, 8 mol% yttria-stabilized zirconia (8YSZ), highlighting its strong potential as a next-generation TBC candidate. The observed ultra-low, amorphous-like thermal conductivity is primarily attributed to enhanced phonon scattering induced by severe lattice distortion and high configurational entropy. Moreover, electrical characterization reveals a highly stable dielectric constant up to 200 °C, accompanied by low dielectric loss, indicating additional potential for electronic and capacitive applications. The room temperature ac conductivity for sample Ba(Ti1/5Zr1/5Hf1/5Sn1/5Mn1/5)O3, Ba(Ti1/5Zr1/5Hf1/5Sn1/5Ce1/5)O3 and Sr(Ti1/4Zr1/4Hf3/20Sn1/4Mn1/10)O3 are 1.05 × 10–6 S/m, 1.01 × 10–6 S/m and 1.63 × 10–6 S/m, respectively, at 1 kHz frequency, which shows the highly insulating nature of the samples. These findings highlight the multifunctional character of high-entropy perovskites and position them as promising candidates for thermal barrier coatings, dielectric components, and a broad range of high-temperature applications. Further investigation is warranted to fully realize and optimize their multifunctional potential.
