High Temperature Far Infrared Emissivity, Reflectivity, and X-ray Absorption of BiFeO$_{3}$

We outline the temperature dependent lattice dynamics of BiFeO$_{3}$ from 4 K to melting by combining far infrared emissivity and reflectivity. The TO low temperature unstable phonon ceases softening at $\sim $400 K. We verified that higher than $\sim $700 K not only thermal fluctuations but also off-stoichiometry chemical disorder are taking place partially reducing long-range order. Strong overlapping, merging, and internal mode band smearing, suggest tripling in an idealized high temperature paraelectric cubic phase. X-ray absorption near edge structure (XANES) shows Fe$^{3+}$ turning into Fe$^{2+}$ while the Bi edge downshift suggests reduction under heating in a very complex configuration. Overall, our structural measurements reveal defect induced irreversible lattice changes in an environment lacking of long-range coherence. By contrast, far infrared wavelengths above Tc $\sim $1090 K do not show this local symmetry breaking only yielding three very broad bands as it would be, in a macroscopic view, if the cubic phase Pmcm (Z=1) is adopted. We do not detect an insulator to metal transition before melting