Ultraviolet Raman spectroscopy of hexagonal LuFeO$_{3}$ films*

Hexagonal LuFeO$_{3}$ films grown by molecular-beam epitaxy on yttria-stabilized zirconia substrates were studied by variable temperature ultraviolet Raman spectroscopy. Hexagonal LuFeO$_{3}$ is a multiferroic that is isostructural to YMnO$_{3}$ at room temperature. LuFeO$_{3}$ spectra at room temperature are consistent with the polar hexagonal \textit{P6}$_{3}$\textit{cm} structure. The temperature evolution of the Raman spectra of a LuFeO$_{3}$ film measured in the range 10--1250 K indicate a transition to a non-polar (likely \textit{P6}$_{3}$\textit{/mmc}) phase; fitting of the temperature dependence of the Raman intensities yields a transition temperature of 1020 $\pm$ 50 K. We also observed a change in the slope of Raman intensity vs. temperature dependence of the most intense phonon peak around 400-450 K, which might indicate another structural transition, possibly to a structure with space group \textit{P6}$_{3}$\textit{mc} (also polar).