Hg2(SeO3)(SO4): the first sulfate selenite with large birefringence explored from d10 transition metal compounds

Abstract

The exploration of new birefringent materials in the d¹⁰ transition metal sulfate selenite system resulted in three new compounds, namely, Hg₂(SeO₃)(SO₄), La₂Hg₃(SeO₃)₄(SO₄)₂(H₂O)₂ and Ag₂Cd(Se₂O₅)(Se_0.3S_0.7O₄), using mild hydrothermal methods. Hg₂(SeO₃)(SO₄) shows a 3D structure composed of 2D mercury selenite layers connected by 1D mercury sulfate chains; La₂Hg₃(SeO₃)₄(SO₄)₂(H₂O)₂ features a novel 3D network composed of 1D lanthanum sulfate chains and 2D mercury oxide layers, which are connected by a SeO₃ triangular pyramid bridge; Ag₂Cd(Se₂O₅)(Se_0.3S_0.7O₄) exhibits a novel 3D framework that consists of selenate silver layers bridged by SO₄ tetrahedra and CdO₆ octahedra. These compounds can remain stable above 250 °C and their optical band gap values are larger than 3.5 eV. The birefringence (Δn) of Hg₂(SeO₃)(SO₄) was calculated to be 0.133 at 532 nm and 0.126 at 1064 nm. Hg₂(SeO₃)(SO₄) was proved as the first reported metal selenite sulfate exhibiting a large birefringence. In addition, the IR spectra, TG-DSC curves and theoretical calculations of the three compounds were studied.