Enhanced ferroelectric polarization in epitaxial (Pb1−xLax)(Zr0.52Ti0.48)O3 thin films due to low La doping

Enhanced polarization is reported in ferroelectric $(\mathrm{P}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x})(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}){\mathrm{O}}_{3}$ (PLZT) thin films at low La doping concentrations. Epitaxial PLZT thin films with varying La concentrations were grown in both (001) and (111) crystallographic orientations using the conducting perovskite oxide $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ as the top and bottom electrodes on $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrates by pulsed laser deposition. Dilute doping of La (0.1--0.5 at. %) was found to enhance the remanent polarizations in the PLZT films irrespective of their orientations. An increase in the remanent polarization by a factor of two is observed in the 0.5 at. % La doped PLZT thin film as compared to the undoped (Pb)$(\mathrm{Z}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}){\mathrm{O}}_{3}$ (PZT) film. The increase in polarization in the PLZT thin films was associated with the tetragonal distortion of the PLZT lattice due to the substitutional doping of La at the Pb sites, as evidenced from x-ray and microstructural analyses. Using the structural and polarization data, a linear correlation between the square of the remanent polarization and crystal-lattice distortion is obtained in the PLZT system, which corroborates with the Landau-Ginsburg-Devonshire thermodynamic model of lattice distortion-induced change in spontaneous polarization. This paper provides a novel route to enhance polarization in PLZT films, which is crucial for the coherent design of high-performance PZT-based ferroelectric and piezoelectric devices.