Effects of rare-earth (Tb, Yb, and Lu)-doping on the structural, electrical and ferroelectric properties of K _0.5 Bi _4.5 Ti ₄ O ₁₅ thin films

The electrical and the ferroelectric properties of pure K _0.5 Bi _4.5 Ti ₄ O ₁₅ and a series of rare-earth-doped K _0.5 RE _0.5 Bi ₄ Ti ₄ O ₁₅ (RE = Tb, Yb, and Lu) thin films deposited on Pt(111)/Ti/SiO ₂ /Si(100) substrates by using a chemical solution deposition method have been investigated. Compared to the pure K _0.5 Bi _4.5 Ti ₄ O ₁₅ thin film, there were no structural changes in the K _0.5 RE _0.5 Bi ₄ Ti ₄ O ₁₅ thin films while the leakage current and the ferroelectric properties were significantly improved. Among the thin films, the K _0.5 Lu _0.5 Bi ₄ Ti ₄ O ₁₅ thin film exhibited wellsaturated hysteresis loops with a large remnant polarization (2P _r ) of 32 μC/cm ² and a coercive field (2E _c ) of 307 kV/cm at an applied electric field of 886 kV/cm. Furthermore, a low leakage current density of 2.95 × 10 ⁻⁹ A/cm ² , which is about two orders of magnitude lower than that of the K _0.5 Bi _4.5 Ti ₄ O ₁₅ thin film, was measured in the K _0.5 Lu _0.5 Bi ₄ Ti ₄ O ₁₅ thin film at an applied electric field of 100 kV/cm. The enhanced electrical and ferroelectric properties observed in the rare-earthdoped K _0.5 RE _0.5 Bi ₄ Ti ₄ O ₁₅ thin films can be correlated to a decrease in the number of ionic defects, such as bismuth and oxygen vacancies, structural distortion, and improved microstructure.