Ali Saha Rafikul, Halder Anita, Fu Desheng, Itoh Mitsuru, Saha-Dasgupta Tanusri, Ray Sugata
School of Materials Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India.
Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector 3, Saltlake, Kolkata 700106, India.
Inorg Chem. 2021 Mar 15;60(6):4068-4075. doi: 10.1021/acs.inorgchem.1c00117. Epub 2021 Mar 4.
In this paper, a comparative structural, dielectric, and magnetic study of two langasite compounds BaTeCoPO (absence of lone pair) and PbTeCoPO (Pb 6s lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in the presence of a stereochemically active lone pair. In the case of PbTeCoPO, mixing of both Pb 6s with Pb 6p and O 2p helps 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 the BaTeCoPO compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric fields confirms room temperature ferroelectricity for PbTeCoPO, which was not the case for BaTeCoPO. A detailed study was carried out to understand the microscopic mechanism of ferroelectricity, which revealed the exciting underlying activity of a polar TeO octahedral unit as well as Pb-hexagon.
在本文中，对两种硅酸镧化合物BaTeCoPO（无孤对电子）和PbTeCoPO（Pb 6s孤对电子）进行了结构、介电和磁性的对比研究，以精确探究在存在立体化学活性孤对电子的情况下室温自发极化的发展情况。在PbTeCoPO的情况下，Pb 6s与Pb 6p以及O 2p的混合有助于孤对电子具有立体化学活性。这种立体化学活性孤对电子在晶胞内引起了较大的结构畸变并产生了极性几何结构，而BaTeCoPO化合物由于不存在任何此类效应而保持非极性结构。因此，在不同电场下的极化测量证实了PbTeCoPO具有室温铁电性，而BaTeCoPO并非如此。为了解铁电性的微观机制进行了详细研究，结果揭示了极性TeO八面体单元以及Pb六边形令人兴奋的潜在活性。
