Unprecedented lattice volume expansion on doping stereochemically active Pb2+ into uniaxially strained structure of CaBa1\u2212xPbxZn2Ga2O7

Pengfei Jiang,Qingzhen Huang,Rihong Cong,Joerg C Neuefeind,Xiaoyan Yang,Mufei Yue,Maxim Avdeev,Tao Yang

doi:10.1038/s41467-020-14759-2

Abstract

Lone pair cations like Pb2+ are extensively utilized to modify and tune physical properties, such as nonlinear optical property and ferroelectricity, of some specific structures owing to their preference to adopt a local distorted coordination environment. Here we report that the incorporation of Pb2+ into the polar “114”-type structure of CaBaZn2Ga2O7 leads to an unexpected cell volume expansion of CaBa1-xPbxZn2Ga2O7 (0 ≤ x ≤ 1), which is a unique structural phenomenon in solid state chemistry. Structure refinements against neutron diffraction and total scattering data and theoretical calculations demonstrate that the unusual evolution of the unit cell for CaBa1-xPbxZn2Ga2O7 is due to the combination of the high stereochemical activity of Pb2+ with the extremely strained [Zn2Ga2O7]4− framework along the c-axis. The unprecedented cell volume expansion of the CaBa1−xPbxZn2Ga2O7 solid solution in fact is a macroscopic performance of the release of uniaxial strain along c-axis when Ba2+ is replaced with smaller Pb2+.

Highlights

Lone pair cations like Pb2+ are extensively utilized to modify and tune physical properties, such as nonlinear optical property and ferroelectricity, of some specific structures owing to their preference to adopt a local distorted coordination environment
The stereochemical activity owing to the Lone pair (LP) electrons of Sn2+ in CsSnBr314, and Pb2+ and Sn2+ in rock-salt chalcogenides PbS15, PbTe15, and SnTe16, is shown to cause a local symmetry lowering in a limited temperature range upon warming
The incorporation of the stereochemically active LP cations into some structures brings intriguing physical properties and some uncommon phenomena. We report another unprecedented phenomenon based on stereochemical activity of LP cations, i.e., cell volume expansion in solid solutions of CaBa1−xPbxZn2Ga2O7 (0 ≤ x ≤ 1) when substituting Ba2+ (r = 1.61 Å in 12-fold coordination) with smaller Pb2+ (r = 1.49 Å in 12-fold coordination)[17]

Summary

Introduction

Lone pair cations like Pb2+ are extensively utilized to modify and tune physical properties, such as nonlinear optical property and ferroelectricity, of some specific structures owing to their preference to adopt a local distorted coordination environment. We report that the incorporation of Pb2+ into the polar “114”-type structure of CaBaZn2Ga2O7 leads to an unexpected cell volume expansion of CaBa1-xPbxZn2Ga2O7 (0 ≤ x ≤ 1), which is a unique structural phenomenon in solid state chemistry. We report another unprecedented phenomenon based on stereochemical activity of LP cations, i.e., cell volume expansion in solid solutions of CaBa1−xPbxZn2Ga2O7 (0 ≤ x ≤ 1) when substituting Ba2+ (r = 1.61 Å in 12-fold coordination) with smaller Pb2+ (r = 1.49 Å in 12-fold coordination)[17]. XRD, as the position for the (004) reflection evolves to lower angles, whereas the position for the (200) reflection shifts to higher angles on the Pb2+-to-Ba2+ substitutions It is firmly corroborated by plotting the lattice parameters against the Pb2+ content (Fig. 1), where the unit cell lattice contracts and expands along the a and caxes, respectively. It is obvious that all the Pb2+-containing compounds possess smaller volumes in comparison with those of Ba2+-containing compounds, which confirms that the observed cell volume expansion in CaBa1−xPbxZn2Ga2O7 is unprecedented

Methods

Results

Conclusion