Ferroelectricity vs Antiferroelectricity in n = 2 Ruddlesden–Popper Phases

Ferroelectric materials – those with a spontaneous, switchable electric polarization – find application in a wide range of electronic devices. We are investigating a new class of ferroelectric materials, the hybrid improper ferroelectrics, which gain their electric polarization through subtle structural distortions. We have observed that while LiSrTa2O7 adopts an improper ferroelectric structure down to the lowest temperatures measured (5 K), the closely related phase Li2SrNb2O7 switches from an improper ferroelectric to proper ferroelectric structure at low temperature. To better understand the competition between the proper and improper ferroelectric states and how the composition of materials favours one or the other, we have prepared a series of related materials and wish to collect high-resolution neutron powder diffraction data to determine their structures.