Fig. 3: PFM and Raman analysis of the BTS850 thin film.

a–c were measured below its Curie temperature at 14 °C, while d–f were measured above its Curie temperature at 21 °C). a PFM phase image of the BTS850 thin film measured at its ferroelectric phase. b Phase-contrast PFM images demonstrating domain switching inside the BTS850 thin film, which arise after applying a ± 10 V DC bias to the tip. c Phase and amplitude switching spectroscopy loops of the BTS850 thin film, demonstrating ferroelectric hysteresis. d PFM phase image of the BTS850 thin film measured at its paraelectric phase. The signature of domain merging can be observed from the circles. e Phase-contrast PFM images of the BTS850 thin film with opposite polarization direction after applying a ± 10 V DC bias to the tip. f Fitted Raman spectrum of the BTS850 thin film and g Raman spectra of all BTS samples with the arrow represent the variation of the peak profile. h Temperature-dependent dielectric permittivity of the BTS850 thin film measured at 100 kHz from 0 °C to 50 °C. The inset figures present the temperature dependency of the alignment structure of polarizations, where the arrows show the polarization profile.