Effect of Ca doping on the properties of Sr₂Bi₄Ti₅O₁₈ ferroelectric thin films

This study examined the effect of Ca doping on the properties of Sr₂Bi₄Ti₅O₁₈ (SBTi) ferroelectric thin films. According to the results of the study, the performance of SBTi thin films are improved by suitable Ca doping. It can be seen from XRD analysis, all of the thin films formed a bismuth layered perovskite structure without other impure phases. SEM shows that the sample with a doping content of 10 mol% has good crystallization, uniform grain size and good film density. Compared with the characteristics of other films, the thin film sample with 10 mol% Ca shows high crystallinity, the lowest Ti³⁺ content, the lowest oxygen vacancy concentration, and with the large remanent polarization 2Pr = 33.5 μC/cm², the double coercive field 2Ec = 182.8 kV/cm; furthermore, the leakage current density is 1.67 × 10⁻⁷ A/cm². The film sample doped with 10 mol% Ca also displays better dielectric properties, with a larger dielectric constant (εr = 795) and lower dielectric loss (tanδ = 0.03) when the test frequency is 10⁵ Hz. The dielectric tunability T = 18.6% at 200 kV/cm and 500 kHz.