Competing polar and antipolar modes as a function of pressure in Li2SrNb2O7

Ferroelectric materials possess a permanent electric dipole, the direction of which can be switched through the application of an external electric field, and as such are widely used in electronic devices like infrared sensors. The existence of a permanent electric dipole can often be linked directly to a symmetry-breaking structural distortion, such as the relative movement of oxide and titanium ions in the prototypical ferroelectric BaTiO3, that imbalances the charge distribution in the structure. Such structural distortions also occur in the layered Ruddlesden-Popper phases, A3B2O7, where they can lead to complex behaviours such as hybrid-improper-ferroelectricity, or competing ferroelectric distortions in the different layers. Li2SrNb2O7 has a so-called ’pseudo-Ruddlesden-Popper’ structure and has been shown to have a complicated combination of ferro- and anti-ferroelectric properties. Through chemical doping, the system Li2Sr1−xCax(Nb1−xTax)2O7 shows a complex phase diagram and we look to investigate the effect of physical (rather than chemical) pressure on the 'parent' phase (Li2SrNb2O7) of this intriguing material family.