Local structure study of multiferroic BiMn2O5 with EXAFS

GILBERTO FABBRIS; GABRIEL ANDREGUETTO; EDUARDO GRANADO; NESTOR MASSA; MARIA JESUS MARTINEZ-LOPE; JOSE ANTONIO ALONSO; GUSTAVO AZEVEDO

Campinas, SP, Brasil

Congreso; International Conference on Synchrotron Radiation on Materials Science – SRMS-6; 2008

Ana Lucia Ferreira,Executive Secretariat SRMS-6 , 13083-970 Campinas - SP, email: srms6@lnls.br

Temperature-dependent EXAFS measurements were utilized to investigate the local structure of BiMn2O5. Mn K-Edge results reveal a  very small temperature dependence of the Debye-Waller factor, suggesting  the MnO polyhedra are rigid.  Above 125 K,   structural distortions in the first coordination shell  are observed at the Bi L3 Egde, in qualitative agreement with  recent results  for  TbMn2O5 by Tyson et al. The present results and synchrotron radiation XRD analysis by Granado et al. suggest low energy vibrational modes associated with rigid rotations of the Mn-O polyhedra are operative at low temperatures, which might explain the low temperature linear expansion coefficient verified for this material. Local structural distortions associated with the ferroelectric phase-transition  around 40K could not be  identified, showing that any local structure change at this transition is very small.