Orientation-dependent dielectric and ferroelectric properties of Pr³⁺-doped Na_0.5Bi_0.5TiO₃ thin films

Pr³⁺-doped Na_0.5Bi_0.5TiO₃ (Pr-NBT) thin films with different preferred orientations including random, (100), and (110) orientations were prepared on Pt/Ti/SiO₂/Si substrates by a chemical solution deposition method combining with a rapid thermal annealing. Effects of the crystallographic orientation on the ferroelectric and dielectric properties of Pr-NBT thin films were investigated. XRD patterns revealed that the preferential orientation degrees of (100)- and (110)-oriented Pr-NBT thin films were 97% and 69%, respectively. The (100)-oriented Pr-NBT thin film has a higher dielectric constant of 1035 compared to the (110)- and randomly oriented ones. Furthermore, a large remnant polarization (2P_r = 31 µC/cm²) was obtained from the highly (100)-oriented Pr-NBT thin film, which is 1.55 times larger than that of the randomly oriented film. The quantitative relationship in dielectric constants between the (100)-, (110)-oriented, and randomly oriented Pr-NBT thin films was calculated using the dipole azimuth model. The calculated result was consistent with experimental measurements. The optimal dielectric tunable property (tunability = 40.8%, FoM = 10.2) is obtained from (100)-oriented films. The highly (100)-oriented Pr-NBT lead-free thin film is promising for use in integrated microelectronic devices.