Abstract A wide bandgap is one of the greatest issues that restrain the photoelectric application of classical ferroelectric oxides in the visible spectrum. Typical approaches to reduce their bandgap, as well as to tune other physical properties (dielectric, piezoelectric …), is to use specific dopants. This work reports the variation by doping of the structural and optical bandgap properties of the Ba0.92Bi0.04Na0.04Ti0.96M0.04O3 (BNBT-M); (M = Ni, Fe, Co) ceramics. Structural refinement shows that all samples are crystallized with a tetragonal phase with a P4mm space group. Detailed analysis of the bond lengths, bond angles, octahedral distortions demonstrates the cooperative effect induced by the Co, Fe, and Ni doping. UV–Vis absorption spectra showed a decrease in the bandgap and increased absorption for longer wavelengths, induced by transitions metal (TM) ions doping. The bandgap narrowing is attributed to the development of new M − O bonds and states in the electronic structure, as the TM ions are incorporated on the Ti site, with simultaneous oxygen vacancies creation. The formation of oxygen vacancies via metal ions doping in BNBT was proven by ESR study. The present investigation can provide useful insight into the understanding and ferroelectrics bandgap tuning for visible-light photovoltaic applications.

中文翻译：

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通过过渡金属掺杂使 Ba0.92Na0.04Bi0.04TiO3 铁电陶瓷带隙变窄，用于光伏应用

摘要 宽带隙是限制经典铁电氧化物在可见光谱中光电应用的最大问题之一。减少带隙以及调整其他物理特性（介电、压电……）的典型方法是使用特定的掺杂剂。这项工作报告了 Ba0.92Bi0.04Na0.04Ti0.96M0.04O3 (BNBT-M) 的结构和光学带隙特性的掺杂变化；(M = Ni, Fe, Co) 陶瓷。结构精修表明所有样品都结晶为具有 P4mm 空间群的四方相。键长、键角、八面体畸变的详细分析证明了 Co、Fe 和 Ni 掺杂引起的协同效应。UV-Vis 吸收光谱显示带隙减小并且对较长波长的吸收增加，由过渡金属 (TM) 离子掺杂引起。带隙变窄归因于电子结构中新 M-O 键和状态的发展，因为 TM 离子结合在 Ti 位点上，同时产生氧空位。ESR研究证明了通过在BNBT中掺杂金属离子形成氧空位。目前的研究可以为可见光光伏应用的理解和铁电带隙调谐提供有用的见解。