Unexpected Phonon Behaviour in BiFexCr1-xO3, a Material System Different from Its BiFeO3 and BiCrO3 Parents

Cameliu Himcinschi; Felix Drechsler; David Sebastian Walch; Akash Bhatnagar; Alexei A Belik; Jens Kortus

doi:10.3390/nano12091607

Unexpected Phonon Behaviour in BiFe_xCr_1-xO₃, a Material System Different from Its BiFeO₃ and BiCrO₃ Parents

Nanomaterials (Basel). 2022 May 9;12(9):1607. doi: 10.3390/nano12091607.

Authors

Cameliu Himcinschi¹, Felix Drechsler¹, David Sebastian Walch^{2

3}, Akash Bhatnagar^{2

3}, Alexei A Belik⁴, Jens Kortus¹

Affiliations

¹ Institute of Theoretical Physics, TU Bergakademie Freiberg, D-09596 Freiberg, Germany.
² Zentrum für Innovationskompetenz SiLi-nano, Martin-Luther-Universität Halle-Wittenberg, D-06120 Halle (Saale), Germany.
³ Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06120 Halle (Saale), Germany.
⁴ International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Ibaraki, Tsukuba 305-0044, Japan.

Abstract

The dielectric function and the bandgap of BiFe_0.5Cr_0.5O₃ thin films were determined from spectroscopic ellipsometry and compared with that of the parent compounds BiFeO₃ and BiCrO₃. The bandgap value of BiFe_0.5Cr_0.5O₃ is lower than that of BiFeO₃ and BiCrO₃, due to an optical transition at ~2.27 eV attributed to a charge transfer excitation between the Cr and Fe ions. This optical transition enables new phonon modes which have been investigated using Raman spectroscopy by employing multi-wavelengths excitation. The appearance of a new Raman mode at ~670 cm^-1 with a strong intensity dependence on the excitation line and its higher order scattering activation was found for both BiFe_0.5Cr_0.5O₃ thin films and BiFe_xCr_1-xO₃ polycrystalline bulk samples. Furthermore, Raman spectroscopy was also used to investigate temperature induced structural phase transitions in BiFe_0.3Cr_0.7O₃.

Keywords: BiFexCr1−xO3; Raman spectroscopy; charge transfer; multiferroics; phase transition; spectroscopic ellipsometry; thin films.

Grants and funding

Open Access Funding by the Publication Fund of the TU Bergakademie Freiberg. This research was funded by German Research Foundation (DFG), Project No. 441856638 and Project No. 31047526, and by Bundesministerium für Bildung und Forschung (BMBF) Project No. 03Z22HN12.