The critical role of stereochemically active lone pair in introducing high temperature ferroelectricity

Rafikul Ali Saha; Anita Halder; Desheng Fu; Mitsuru Itoh; Tanusri Saha-Dasgupta; Sugata Ray

paper

The critical role of stereochemically active lone pair in introducing high temperature ferroelectricity

arXiv:2102.02451

Abstract

In this paper a comparative structural, dielectric and magnetic study of two langasite compounds Ba $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ (absence of lone pair) and Pb $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ (Pb $^{2 +}$ 6 $s^{2}$ lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in presence of stereochemically active lone pair. In case of Pb $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ , mixing of both Pb 6 $s$ with Pb 6 $p$ and O 2 $p$ help the lone pair to be stereochemically active. This stereochemically active lone pair brings a large structural distortion within the unit cell and creates a polar geometry, while Ba $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric field confirms room temperature ferroelectricity for Pb $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ , which was not the case of Ba $_{3}$ TeCo $_{3}$ P $_{2}$ O $_{14}$ . Detailed study was carried out to understand the microscopic mechanism of ferroelectricity which revealed the exciting underlying activity of poler TeO $_{6}$ octahedral unit as well as Pb-hexagon.