Band gap tuning and orbital mediated electron–phonon coupling in HoFe1−xCrxO3 (0 ≤ x ≤ 1)

Kotnana, G and J, Suryanarayana (2015) Band gap tuning and orbital mediated electron–phonon coupling in HoFe1−xCrxO3 (0 ≤ x ≤ 1). Journal of Applied Physics, 118 (124101). pp. 1-7. ISSN 0021-8979

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Abstract

We report on the evidenced orbital mediated electron–phonon coupling and band gap tuning in HoFe1−xCrxO3 (0 ≤ x ≤ 1) 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+ and Cr3+ at around 670 cm−1, this observation is explained on the basis of Franck-Condon mechanism. Optical absorption studies infer that there exists a direct band gap in the HoFe1−xCrxO3 (0 ≤ x ≤ 1) 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.

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