Thermally stable dielectric responses in uniaxially (001)-oriented CaBi₄Ti₄O₁₅ nanofilms grown on a Ca₂Nb₃O₁₀-nanosheet seed layer

To realize a high-temperature capacitor, uniaxially (001)-oriented CaBi₄ Ti₄O₁₅ films with various film thicknesses were prepared on (100) c SrRuO₃/Ca₂Nb₃O₁₀-nanosheet/glass substrates. As the film thickness decreases to 50 nm, the out-of-plane lattice parameters decrease while the in-plane lattice ones increase due to the in-plane tensile strain. However, the relative dielectric constant (μ r) at room temperature exhibits a negligible degradation as the film thickness decreases to 50 nm, suggesting that μ r of (001)-oriented CaBi₄Ti₄O₁₅ is less sensitive to the residual strain. The capacitance density increases monotonously with decreasing film thickness, reaching a value of 4.5 μF/cm² for a 50-nm-thick nanofilm, and is stable against temperature changes from room temperature to 400 °C irrespective of film thickness. This behaviour differs from that of the widely investigated perovskite-structured dielectrics. These results show that (001)-oriented CaBi₄Ti₄O₁₅ films derived using Ca₂Nb₃O₁₀-nanosheets as seed layers can be made candidates for high-temperature capacitor applications by a small change in the dielectric properties against film thickness and temperature variations.