Electron diffraction study of the space group of Bi 5 Ti 3 FeO 15 multiferroic ceramic.

BiTiFeO (pentabismuth trititanium iron pentadecaoxide), which is a multiferroic four-layer Aurivillius phase compound, has received much attention in recent years. However, three mutually inconsistent orthorhombic space groups, i.e. A2am, Fmm2 and Pnn2, have been reported for the room-temperature phase of BiTiFeO by X-ray and neutron diffraction investigations. Here, electron diffraction results are presented and discussed for the first time to unambiguously clarify the room-temperature space group of ceramic BiTiFeO. It has been found that all the observed reflections from the ceramic agree with those expected in A2am, while the observed reflections 011, 013 and 015 should be forbidden in the case of Fmm2, and no 107 and 109 reflections were observed although allowed for Pnn2. The present study has demonstrated that the space group of BiTiFeO ceramic is A2am rather than Fmm2 or Pnn2, an identification that proved to be a challenge for X-ray diffraction. On the basis of the space group A2am, the lattice parameters of the BiTiFeO ceramic were calculated from its X-ray diffraction data.