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.

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.