Strain driven structural phase transformations in dysprosium doped BiFeO3 ceramics

A detailed powder neutron and synchrotron diffraction study coupled with a complementary Raman spectroscopy study of the addition of Dy3+ into BiFeO3 ceramics is reported here. It can be seen that the addition of Dy3+ destabilises the polar R3c symmetry due to chemical strain effects arising from the large size mismatch between the two A-site cations ( Dy3+ and Bi3+). This results in a lowering of the symmetry to a polar Cc model and in the range 0.05 <= x <= 0.30 in Bi-1 - (x)Dy(x)FeO3 competition develops between the strained polar Cc and non-polar Pnma symmetries with the Cc model becoming increasingly strained until approximately x = 0.12 at which point the Pnma model becomes favoured. However, phase co-existence between the Cc and Pnma phases persists to x = 0.25. Preliminary magnetic measurements also suggest weak ferromagnetic character which increases in magnitude with increasing Dy3+ content. Preliminary electrical measurements suggest that whilst Bi(0.95)Dy(0.05)FeO3 is most likely polar; Bi(0.70)Dy(0.30)FeO3 shows relaxor-type