Band gap tuning and orbital mediated electron phonon coupling in $HoFe_{1-x}Cr_xO_3$

TL;DR

This study investigates how orbital-mediated electron-phonon coupling and band gap tuning in HoFe1-xCrxO3 compounds are influenced by Fe and Cr substitution, revealing insights relevant for optoelectronic device development.

Contribution

It demonstrates the effect of Fe and Cr substitution on electron-phonon coupling and band gap tuning in HoFe1-xCrxO3, highlighting the role of orbital interactions and charge transfer mechanisms.

Findings

Electron-phonon coupling is sensitive to Fe and Cr presence.

Band gap decreases up to x=0.5, then increases beyond.

Oxygen breathing mode activated via charge transfer.

Abstract

We report on the evidenced orbital mediated electron phonon coupling and band gap tuning in HoFe1-xCrxO3 compounds. From the room temperature Raman scattering, it is apparent that the electron-phonon coupling is sensitive to the presence of both the Fe and Cr at the B-site. Essentially, an Ag like local oxygen breathing mode is activated due to the charge transfer between Fe3+ - Cr3+ at around 670 cm-1, this observation is explained on the basis of Franck-Condon (FC) mechanism. Optical absorption studies infer that there exists a direct band gap in the HoFe1-xCrxO3 compounds. Decrease in band gap until x = 0.5 is ascribed to the broadening of the oxygen p orbitals as a result of the induced spin disorder due to Fe3+ and Cr3+ at B site. In contrast, the increase in band gap above x = 0.5 is explained on the basis of the reduction in the available unoccupied d - orbitals of Fe3+ at the conduction band. We believe that above results would be helpful for the development of the optoelectronic devices based on the ortho-ferrites.