Electronic and optical properties of Y-doped $\hbox {BaBiO}_{3}$

Abstract

We investigate the nature of bond disproportionation in $\hbox {BaBi}_{0.9}\hbox {Y}_{0.1}\hbox {O}_{3}$ (BYBO) and its manifestation in the valence band and the optical absorption spectra. Our room-temperature (RT) structural results show that both the parent and the doped (BYBO) compounds stabilise in monoclinic structure but with a change in space group from I2/m to P21/n on Y doping. The Raman scattering studies suggest decrement in the breathing mode distortion of $\hbox {BiO}_{6}$ octahedra. The valence band spectra show an increase in the gap and close to the Fermi edge, we observe significant modifications in the fine structures on Y doping. These were studied using band structure calculations under TB-mBJ. The results show that the electronic states of the Y ions play significant role in driving the electronic structure. We also observe the importance of O 2p holes and also transfer of electrons from O 2p to Bi1 6s, Bi2 6s, and Y states to bring about bond disproportionation in the doped compound. The intensity variations and the features in the optical absorption spectra were understood based on the E vs k point calculations performed in the irreducible part of the Brillouin zone. The behaviour of the gap on doping is also in line with the calculations and optical absorption studies. The behaviour of the optical absorption spectra suggests possible use in solar cell and optical sensor applications. A composite of the doped compound with $\hbox {BaTiO}_{3}$ may find applications in the field of high-energy density capacitor. We believe that our results will be helpful in understanding the role of the electronic states of the dopants in superconductivity, especially in comparison with the monoclinic phase exhibited in the superconducting phase of $\hbox {BaPb}_{0.75}\hbox {Bi}_{0.25}\hbox {O}_{3}$.

Graphic abstract