# Weak Ferroelectricity in n = 2 pseudo Ruddlesden-Popper-type niobate Li2SrNb2O7

## TL;DR

This study reveals weak ferroelectricity in Li2SrNb2O7, a n=2 Ruddlesden-Popper-type niobate, showing coexistence of polarization and anti-ferroelectric-like response below 217 K, with insights from first-principles calculations and X-ray diffraction.

## Contribution

It demonstrates the presence of weak ferroelectricity in LSNO and clarifies its polar structure, offering new design perspectives for related materials.

## Key findings

- Weak ferroelectricity observed below 217 K.
- Polar P21cn structure identified for LSNO.
- Coexistence of in-plane anti-ferroelectric displacement and out-of-plane polarization.

## Abstract

Li2SrNb2O7 (LSNO) crystallizes in a structure closely related to n = 2 Ruddlesden-Popper-type compounds, which is gen-erally formed by intergrowth of 2-dimensional perovskite-type blocks and rocksalt-type layers. The present study demonstrates a coexistence of spontaneous polarization and anti-ferroelectric-like nonlinear response in LSNO at 80 K, suggesting a weak ferroelectricity below the phase transition temperature of 217 K. A combination of first-principles cal-culations and single crystal x-ray diffractions clarifies a polar P21cn structure for the ground state of LSNO, where an in-plane anti-ferroelectric displacement and an out-of-plane polar shift simultaneously take place. The present study offers a new perspective to design ferroelectric and antiferroelectric materials with Ruddlesden-Popper-type compounds.

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Source: https://tomesphere.com/paper/1906.07501