Polarized Raman spectroscopy of nearly-tetragonal BiFeO$_3$ thin films

TL;DR

This study uses polarized Raman spectroscopy to analyze the phase structure of strained BiFeO$_3$ thin films, revealing their monoclinic symmetry and phase coexistence, which advances understanding of their structural properties under strain.

Contribution

It provides the first experimental evidence that nearly-tetragonal BiFeO$_3$ films are monoclinic ($Cc$ symmetry) rather than tetragonal, and maps phase coexistence at different film thicknesses.

Findings

Nearly-tetragonal BiFeO$_3$ films are monoclinic ($Cc$ symmetry).

Localized coexistence of BFO-T and BFO-R phases depends on film thickness.

Raman mapping reveals phase distribution and coexistence in strained films.

Abstract

BiFeO$_3$ thin films can be epitaxially stabilized in a nearly-tetragonal phase under a high biaxial compressive strain. Here we investigate the polarized Raman spectra of constrained BiFeO$_3$ films with tetragonal-like (BFO-T), rhombohedral-like (BFO-R) and multiphase (BFO-T+R) structure. Based on analysis of the number and symmetry of the Raman lines, we provide strong experimental evidence that the nearly-tetragonal films are monoclinic ($Cc$ symmetry) and not tetragonal $(P4mm)$. Through the Raman mapping technique we show localized coexistence of BFO-T and BFO-R phases with the relative fraction dependent on the film thickness.