Determination of Local structure – ferroelectric property relationships in (La,Nd)1/3NbO3

Improving capacitors for power electronic applications requires new dielectric materials that can withstand high electric fields. Relaxor ferroelectrics (RFE) and Quasi linear dielectrics (QLD) are able to achieve this, whilst maintaining a high permittivity. Typically, REF and QLD materials are very chemically complex so the structural effects that cause this behaviour are hard to determine. Our recent work on La1/3NbO3 and Nd1/3NbO3 has shown that at cryogenic temperatures, RFE and incipient ferroelectric behaviours (which have the same permittivity-temperature profiles as QLD) are observed. Both these materials are not chemically complex and have orthorhombic Cmmm crystal symmetry at RT. Neutron studies had previously been conducted at cryogenic temperatures for La1/3NbO3, however, a phase transition which typically coincides with a peak in permittivity was not observed. In similar materials that have observed RFE behaviour with no phase changes, local structural effects (octahedral tilting and cation displacements) have been determined to be the cause for a peak in permittivity. We request 2 days of beam-time on POLARIS to collect total neutron scattering data to investigate the local structure of La1/3NbO3 and Nd1/3NbO3 at room temperature and 4 K. This will identify local atomic positions and structural distortions which will explain how these two materials with the same crystal structure at RT can show different ferroelectric behaviours.