Crystal structure of Bi1−xTbxFeO3 from high-resolution neutron diffraction

Samples of Bi1−xTbxFeO3, with x=0.05, 0.10, 0.15, 0.20 and 0.25, have been synthesised by solid state reaction. The crystal structures of the perovskite phases, characterised via Rietveld analysis of high resolution powder neutron diffraction data, reveal a structural transition from the R3c symmetry of the parent phase BiFeO3 to orthorhombic Pnma symmetry, which is complete for x=0.20. The x=0.10 and 0.15 samples are bi-phasic. The transition from a rhombohedral to orthorhombic unit cell is suggested to be driven by the dilution of the stereochemistry of the Bi3+ lone pair at the A-site. The G-type antiferromagnetic spin structure, the size of the ordered magnetic moment (∼3.8 μB) and the TN (∼375 °C) are relatively insensitive to increasing Tb concentrations at the A-site.

High resolution neutron powder diffraction has been used to study the evolution of the RT crystal structure of Bi1−xTbxFeO3 (0.05≤x≤0.25) with terbium content. A transition from polar R3c to centrosymmetric Pnma symmetry is observed. The antiferromagnetic ordering temperature and size of the ordered magnetic moment are relatively insensitive to the change of crystal structure.Figure optionsDownload as PowerPoint slideHighlights
► Structural transition from polar R3c symmetry to non-polar Pnma symmetry occurs.
► Behaviour is rationalised via dilution of the stereochemical nature of the Bi lone pair.
► Magnetic properties are largely unaffected.