High Temperature Far Infrared Emissivity, Reflectivyity, and X-ray Absorption of BiFeO3

NESTOR E. MASSA; LEIRE DEL CAMPO; DOMINGOS DE SOUSA MENESES; PATRICK ECHEGUT; GILBERTO F.L. FABBRIS; GUSTAVO AZEVEDO; MARÍA JESUS MARTÝNEZ-LOPE; JOSÉ ANTONIO ALONSO

Portland. Oregon, U.S.A.

Congreso; American Physical Society March Meeting; 2010

American Physical Society

High Temperature Far Infrared Emissivity, Reflectivyity, and X-ray Absorption of BiFeO3 N.E. MASSA, LANAIS EFO-CEQUINOR, UNLP, La Plata, Argentina, L. DEL CAMPO, D. DE SOUSA MENESES, P. ECHEGUT, CNRS-CEMHTI, Orleans, France , G.F.L. FABBRIS, G. AZEVEDO, LNLS, Campinas, Brazil, M.J.MARTINEZ-LOPE, J.A. ALONSO, ICMM-CSIC, Madrid, Spain | We outline the temperature dependent lattice dynamics of BiFeO3 from 4K to melting by combining far infrared emissivity and reflectivity. TheTO low temperature unstable phonon ceases softening at »400 K. We verified that higher than »700 K not only thermal fluctuations but also 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 Fe3+ turning into Fe2+ 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 »1090 K do not show this local symmetry breaking only yielding three very broad bands as it would be, insulator to metal transition before melting