Band gap tuning in samarium-modified bismuth titanate ferroelectric via iron doping for photovoltaic applications

Abstract

The wide band gap of complex oxides is one of the critical challenges restricting their usage in photovoltaic cells. Therefore, examinations of their photoelectric characteristics have increasingly concentrated on materials with a low band gap. This work investigated the effects of iron doping on samarium-modified Bi₄Ti₃O₁₂-based oxides (BSmT) made via a solid reaction approach to control the band gap of complex oxides. X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS) were used to study the synthesized materials’ structural, optical, and oxygen vacancies. Doping with Fe atoms significantly increased the tunability of the band gap from 3.20 eV to 1.81 eV without violating symmetry. The tuning of bandgap energy in this system was explained based on structural distortion and the formation of oxygen vacancies. This work examined the ferromagnetism and ferroelectricity ordering of the sintered BSmT:F0% and BSmT:F10% samples at room temperature to demonstrate the multiferroelectricity behavior. The findings indicate unsaturated P-E hysteresis loops driven by domain pinning caused by oxygen vacancy formation near domain boundaries. Simultaneously, significant S-type M-H hysteresis loops showed weak ferromagnetic ordering. The findings in this study are encouraging for the development of intrinsic multiferroics for photovoltaic devices for future applications.

Keywords:

• Ferroelectrics
• bandgap
• absorption spectra
• octahedral distortion
• oxygen vacancy
• ferroelectric
• ferromagnetic

Acknowledgments

The authors gratefully acknowledge the experimental facilities supported by CNPq and FAPESP to the Groupo de Materiais Ferroicos (GMF), at the Physics Department/UFSCar. The authors would also like to express their gratitude for the XPS and VSM instrumental research facilities made available by the VRM lab at the Institute of Physics (USP) and the IAS lab at the Physics Department at (UEM). FAPESP (Grant numbers 2017/13769-1 and 2023/05716-6) is gratefully acknowledged by Dr. Alkathy and Prof. Eiras.

Disclosure statement

No potential conflict of interest was reported by the author(s).