Strain driven structural phase transformations in dysprosium doped BiFeO3 ceramics

Abstract

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−xDy_xFeO₃ 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_0.95Dy_0.05FeO₃ is most likely polar; Bi_0.70Dy_0.30FeO₃ shows relaxor-type behaviour.