Effects of rare earth metal (Gd and Dy) doping on the structural and electrical properties of K_0.5Bi_4.5Ti₄O₁₅ thin films

K_0.5Bi_4.5Ti₄O₁₅ (KBTi), K_0.5Bi₄Gd_0.5Ti₄O₁₅ (KBGdTi), and K_0.5Bi₄Dy_0.5Ti₄O₁₅ (KBDyTi) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method to investigate the effects of doping on the structural, electrical, and ferroelectric properties. Doping with Gd- and Dy-ions clearly leads to notable improvements in the electrical and ferroelectric properties. Among the thin films, the KBGdTi thin film exhibited a low leakage current density of 1.83×10^–9 A/cm² at 100 kV/cm, a large ferroelectric polarization of 49 μC/cm², and a low coercive electric field of 398 kV/cm at an applied electric field of 885 kV/cm. A fatigue endurance study showed that the switchable polarization was reduced by only 4% of the initial value after 1.44×10¹⁰ switching cycles for the Gd- and Dy-doped KBTi thin films. The improvements in electrical and ferroelectric properties of the Gd- and Dy-doped KBTi thin films were explained on the basis of microstructural change, a decrease in the number of oxygen vacancies, and structural distortion caused by doping with Gd- and Dy-ions.