Possible incommensurate modulation and actual crystal structure of BiMg0.5Ti0.5O3 - a lead-free structural analogue of the prototype antiferroelectric PbZrO3

Complex oxides with antiferroelectric behaviour are promising for energy-storage applications and therefore are under intense investigation. Lead zirconate (PbZrO3, PZ) is a prototype perovskite antiferroelectric. In spite of a long history of experimental and theoretical studies, PZ continues to surprise us with new effects and features. “Missed” incommensurate modulation in pure PZ and a 3-D electric dipole structure in slightly doped PZ are the recent examples.
BiMg0.5Ti0.5O3 (BMT) synthesised under high pressure has been demonstrated to be a lead-free structural analogue of PZ. We characterised the BMT structure using laboratory XRD data. It was impossible to find precise positions of oxygen atoms; therefore, the oxygen octahedra in BMT were assumed as rigid and the space group was concluded to be either Pnnm or Pbam. We have recently conducted a neutron diffraction study of BMT-based orthorhombic phase and found new features of this phase, which was initially considered to be Pbam as that in pure PZ. This suggests that the real crystal structure of BMT is more complex and can realise the peculiarities, which are missed or hidden in PZ.
We propose to study the crystal structure of BMT as well as its temperature behaviour using a neutron powder diffraction. Correct crystallographic data will be used in calculations aiming at identification of the competing interactions and open a way to induce and control an incommensurate modulation in lead-free alternatives of PZ.