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We report a Raman scattering investigation of multiferroic bismuth ferriteBiFeO3 epitaxial (c-axis oriented) thin films from -192 to 1000C. Phononanomalies have been observed in three temperature regions: in the gamma-phasefrom 930C to 950C; at ~370C, Neel temperature (TN), and at ~123C, due to aphase transition of unknown type (magnetic or structural). An attempt has beenmade to understand the origin of the weak phonon-magnon coupling and thedynamics of the phase sequence. The disappearance of several Raman modes at~820C (Tc) is compatible with the known structural phase transition and thePbnm orthoferrite space group assigned by Arnold {\it et al.} \cite{arnold:09}.The spectra also revealed a {\it non-cubic} $\beta$-phase from 820-930\dc andthe same {\it non-cubic} phase extends through the $\gamma$-phase between930-950\dc, in agreement with Arnold {\it et al.} \cite{arnold2:09}, and anevidence of a cubic $\delta$-phase around 1000\dc in thin films that is notstable in powder and bulk. Such a cubic phase has been theoretically predictedin \cite{vasquez:prb09}. Micro-Raman scattering and X-ray diffraction showed nostructural decomposition in thin films during the thermal cycling from22-1000\dc.

Phonon Spectroscopy Near Phase Transition Temperatures in Multferroic BiFeO3 Epitaxial Thin Films