Chemical Compensation Challenges in Processing Antiferroelectric PbZrO₃ Thin Films

The electric field-induced antipolar-to-polar phase transition in antiferroelectric materials is accompanied by large changes in the structural and functional response, making them attractive for many applications ranging from pulsed energy capacitors to high-strain-high (blocking-)-force actuators, solid-state heating and cooling systems, and optoelectronic devices. PbZrO₃, as an end member of the PZT, (x)-PbZr_1-x Ti _x O₃, solid solution, has been the subject of many studies. However, processing of perovskite PbZrO₃ is extremely challenging due to phase instabilities induced by Pb loss at the temperatures necessary for perovskite crystallization. Here, we discuss the challenges associated with Pb loss, as well as its compensation through bulk Pb overstoichiometry and interfacial PbO additions, in chemical solution processed, highly oriented PbZrO₃ thin films. For both 042_o- and 001_o-oriented (o-orthorhombic distortion) PbZrO₃ thin films, the crystallization interfaces are the most important contributors to Pb loss and off-stoichiometric outcomes, and no single approach was sufficient to address these challenges. Pb-rich and Pb-deficient nonperovskite phases including ZrO _x were only observable through microscopic characterization, and X-ray diffraction alone could not rule out the presence of such secondary phases. "Ideal" macroscopic antiferroelectric polarization-electric field double hysteresis curves were observed despite (at times) the large presence of secondary phases. However, reduced saturation polarization and increased phase transition electric fields were observed concomitantly with the presence of secondary phase(s) and tentatively assigned to the voltage drop across the ZrO _x nanocrystals. Based on these results, it is imperative that the presence of secondary phases always be addressed (beyond X-ray diffraction spectra) in order to correctly evaluate the properties of antiferroelectric films.