Hg4(Te2O5)(SO4): A Giant Birefringent Sulfate Crystal Triggered by a Highly Selective Cation

Sulfate crystals are often criticized for their low birefringence. The small anisotropic SO4 group is becoming the biggest bottleneck hindering the application of sulfates in optical functional materials. In this study, we report a new method to significantly enhance the birefringence of sulfates. The title compound increases the birefringence recording of sulfates to 0.542@546 nm, which is significantly larger than that of the commercial birefringent crystal of TiO2 (0.306@546.1 nm). At the infrared wavelength, the birefringence of Hg4(Te2O5)(SO4) can be up to 0.400@1064 nm, which is also much larger than the infrared birefringent crystal of YVO4 (0.209@1064 nm). In addition, it also has a wide transparency range, high thermal stability, and excellent environmental stability, making it a potential birefringent material. Hg4(Te2O5)(SO4) features a novel two-dimensional layered structure composed of [Hg4(Te2O5)]2+ layers separated by isolated (SO4)2- tetrahedra. This compound was designed by introducing a highly selective cation in a tellurite sulfate system. The low valence low coordination cations connect with tellurite groups only, making the sulfate isolated in the structure. The steric repulsive action of the isolated SO4 tetrahedra may regulate the linear and lone pair groups arranged in a way that favors large birefringence. This method can be proven by theoretical calculations. PAWED studies showed that the large birefringence originated from the synergistic effect of (Hg2O2)2-, (Te2O5)2-, and (SO4)2- units, with a contribution ratio of 42.17, 37.92, and 19.88%, respectively. Our work breaks the limitation of low birefringence in sulfates and opens up new possibilities for their application as birefringent crystals.

Y2(Te4O10)(SO4): a new sulfate tellurite with a unique Te4O10 polyanion and large birefringence

Y₂(Te₄O₁₀)(SO₄), featuring a unique (Te₄O₁₀)⁴⁻ polyanion, exhibits a large birefringence (0.124@1064), wide energy band gap (4.1 eV) and high thermal stability (>700 °C), which make it a potential birefringent material.

Pb2Cd(SeO3)2X2 (X = Cl and Br): two halogenated selenites with phase matchable second harmonic generation

The second harmonic generation (SHG) efficiencies of Pb₂Cd(SeO₃)₂X₂ (X = Cl and Br) are higher than that of commercial KDP (KH₂PO₄) and their laser damage thresholds are 30 times more than that of AGS (AgGaS₂).

Alkali earth MOx (x = 6, 7, 9, 12) polyhedra tuned cadmium selenites with different dimensions and diverse SeO32− coordinations

Alkali earth cation-tuned framework of cadmium selenites resulting in evolvement of the structures from high dimension to low dimension.

Structural and magnetic studies on three new mixed metal copper(II) selenites and tellurites

Three new transition metal copper(II) selenites or tellurites, namely, CdCu(SeO3)2 (1), HgCu(SeO3)2 ()2, and Hg2Cu3(Te3O8)2 (3), have been obtained by conventional hydrothermal reactions of CdO (or Hg2Cl2), CuO and SeO2 (or TeO2). Compounds 1 and 2 are isostructural and crystallize in P2(1)/c. Their structures feature a 3D anionic framework of Cu(SeO3)2(2-) with 1D channels of eight-membered rings (MRs) along the c-axis and a-axis, respectively, which are filled by Cd(2+) or Hg(2+) cations. Compound 3 crystallizes in a tetragonal system of space group P42(1)2. Its structure is characterized by a [Cu3(Te3O8)2](2-) honeycomb layer composed of [Te3O8](4-) anions interconnected by Cu(2+) ions with 1D channels of 8-MRs along the c-axis. TOPOS analysis indicates that the copper(ii) tellurite layer exhibits a new topological structure with a Schläfli symbol of {4(6)·8(9)}(2){4(6)}(3). The above anionic copper(II) tellurite layers are further linked by dumbbell Hg2(2+) cations to form a novel 3D framework. Magnetic measurements based on magnetic susceptibility and heat capacity indicate that compounds 1 and 2 show a spin-singlet ground state with a spin gap based on the [Cu2O8](12-) dimeric model, whereas compound e3 xhibits a 2D spin-system with an antiferromagnetic ordering around 25 K correlated with its honeycomb [Cu3(Te3O8)2](2-) layer. Furthermore, crystalline structures, thermal stabilities, IR spectra and UV-Vis diffuse reflectance spectra have also been studied.