In situ investigation of thermally influenced phase transformations in (pb0.92sr0.08) (zr0.65ti0.35)o3 thin films using micro-raman spectroscopy and x-ray diffraction

Thin films of ferroelectric strontium-doped lead zirconate titanate [PSZT, (Pb_0.92Sr_0.08)(Zr_0.65Ti_0.35)O₃] deposited by RF magnetron sputtering have been analyzed by in situ analysis techniques. The in situ techniques employed for this study include micro-Raman spectroscopy and X-ray diffraction (XRD), and variations in thin film structure and orientations for temperatures up to 350degC and 750degC for the respective techniques have been studied. The samples analyzed were PSZT thin films deposited on platinum-coated silicon substrates at either room temperature or at 750degC. In situ measurements using micro-Raman spectroscopy and XRD techniques have been used to identify the Curie point for poly-crystalline PSZT thin films and to determine the temperature-activating significant grain growth for room-temperature-deposited PSZT thin films. To study the presence of hysteresis, analysis was carried out during both temperature ramp-up and ramp-down cycles. Raman measurements showed expected bands (albeit weak), and the in situ measurements have detected variations in the crystal structure of the thin film samples, with negligible variations between the heating and cooling cycles. A combination of the Raman and XRD results has shown that the temperature activating significant grain growth for the room-temperature deposited films is about 275degC and the Curie point lies between 325 and 400degC. This relatively high Curie point makes these films suitable for wide temperature range applications.

I. Introduction

The lead zirconate titanate (PZT) family of compounds, especially undoped PZT, is used in a wide variety of commercial applications (e.g., nano-positioning stages). PZT compounds are popular due to the relatively high piezoelectric response exhibited by this class of materials, thereby enabling more sensitive sensors, actuators, or transducers [1], [2]. The addition of strontium as an Asite dopant to the perovskite ABO₃ structure of PZT (resulting in strontium-doped lead zirconate titanate, PSZT) enhances the piezoelectric behavior [3]–[5]. In addition to the high levels of piezoelectric response, PZT compounds have a relatively high Curie point. The Curie point is the temperature above which the unit cell of piezoelectric compounds transforms from asymmetric tetragonal or rhombohedral arrangement to symmetric cubic arrangement; this renders them non-piezoelectric.