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.