Intrinsic and extrinsic contributions in the ferroelectric response of chemically synthesized BiFeO3-xPbTiO3 thin films

Multiferroic (BiFeO3)1−x-(PbTiO3)x (1−x)BF−xPT thin films exhibit very high electromechanical properties in the vicinity of the morphotropic phase boundary (MPB), making them important candidates for use in several modern device applications. However, preparing high-quality (1−x)BF−xPT thin films is challenging due to the high conductivity caused by oxygen vacancies produced during the synthesis process. This study aims to understand the effect of size and porosity density on the electrical properties of (1−x)BF−xPT thin films. A series of (1−x)BF−xPT solid solution thin films were fabricated using the spin-coating method on Pt/TiO2/SiO2/Si(100) substrates through chemical solution deposition. X-ray diffraction studies revealed a polycrystalline structure. Surface SEM images showed that the films have a uniform surface with average grain sizes ranging between 50 and 200 nm and an average film thickness of 1.5 μm. A decrease in average pore size and an increase in the number of pores were observed with the increase in PT concentration in the prepared films. Ferroelectric characterization revealed that the films exhibit room-temperature ferroelectric hysteresis loops. Sources of various contributions to polarization were extracted from hysteresis loops, including true ferroelectric switching and space charge contributions. Thin films with 0.30 < x < 0.45 show higher remanent and saturation polarization values, suggesting that these compositions exhibit the MPB. The highest remanent polarization value (PR = 16.68 μC/cm2) was observed for the thin film with x = 0.40. The correlation between the phase, composition, film morphology, and ferroelectric response is described and discussed.