Na₄MgM₂Se₆ (M = Si, Ge): The First Noncentrosymmetric Compounds with Special Ethane-like [M₂Se₆]^6– Units Exhibiting Large Laser-Damage Thresholds

Two new noncentrosymmetric compounds, Na₄MgM₂Se₆ (<b>I</b>, M = Si; <b>II</b>, M = Ge), that contain special ethane-like [M₂Se₆]^6– units were reported for the first time. Remarkably, they exhibit high laser-damage thresholds [9 (<b>I</b>) and 7 (<b>II</b>) × benchmark AgGaS₂] and moderate second-harmonic-generation responses with type I phase matching

Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn): New Infrared Nonlinear Optical Materials with Strong Second Harmonic Generation Effects and High Laser-Damage Thresholds

A new family of noncentrosymmetric isostructural compounds, Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn), was successfully synthesized. They crystallize in the tetragonal space group <i>P</i>4̅<i>c</i>2 with <i>Z</i> = 2. Their major structures are composed of infinite cross-connected _<i>∞</i>(HgS₃)_<i>n</i> chains and isolated [MS₄] ligands and show the interesting tunnel features. Interestingly, compared with the structures of A₂Hg₃M₂S₈ (A = alkali metal, Na–Cs), it can be found that the structural symmetries show a gradually rising tendency from Cs to Na analogues as a result of cation size effect, which rarely exists in quaternary alkali metal chalcogenides. Property measurements show that title compounds exhibit strong second harmonic generation (SHG) effects with a phase-matching behavior at 2.09 μm, wide transparency range in the infrared (IR) region, and large laser-damage thresholds (LDTs). Remarkably, Na₂Hg₃Si₂S₈ and Na₂Hg₃Ge₂S₈ achieve the suitable balance between large SHG effects (1.3 and 2.2 × benchmark AgGaS₂) and high LDTs (4.5 and 3 × AgGaS₂), respectively, and can be expected to be potential nonlinear optical (NLO) candidates in the IR region. Moreover, band structures and NLO properties of title compounds are also theoretically studied, and the calculated NLO coefficients are consistent with the experimental observations

Na₄MgM₂Se₆ (M = Si, Ge): The First Noncentrosymmetric Compounds with Special Ethane-like [M₂Se₆]^6– Units Exhibiting Large Laser-Damage Thresholds

Two new noncentrosymmetric compounds, Na₄MgM₂Se₆ (<b>I</b>, M = Si; <b>II</b>, M = Ge), that contain special ethane-like [M₂Se₆]^6– units were reported for the first time. Remarkably, they exhibit high laser-damage thresholds [9 (<b>I</b>) and 7 (<b>II</b>) × benchmark AgGaS₂] and moderate second-harmonic-generation responses with type I phase matching

Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn): New Infrared Nonlinear Optical Materials with Strong Second Harmonic Generation Effects and High Laser-Damage Thresholds

A new family of noncentrosymmetric isostructural compounds, Na₂Hg₃M₂S₈ (M = Si, Ge, and Sn), was successfully synthesized. They crystallize in the tetragonal space group <i>P</i>4̅<i>c</i>2 with <i>Z</i> = 2. Their major structures are composed of infinite cross-connected _<i>∞</i>(HgS₃)_<i>n</i> chains and isolated [MS₄] ligands and show the interesting tunnel features. Interestingly, compared with the structures of A₂Hg₃M₂S₈ (A = alkali metal, Na–Cs), it can be found that the structural symmetries show a gradually rising tendency from Cs to Na analogues as a result of cation size effect, which rarely exists in quaternary alkali metal chalcogenides. Property measurements show that title compounds exhibit strong second harmonic generation (SHG) effects with a phase-matching behavior at 2.09 μm, wide transparency range in the infrared (IR) region, and large laser-damage thresholds (LDTs). Remarkably, Na₂Hg₃Si₂S₈ and Na₂Hg₃Ge₂S₈ achieve the suitable balance between large SHG effects (1.3 and 2.2 × benchmark AgGaS₂) and high LDTs (4.5 and 3 × AgGaS₂), respectively, and can be expected to be potential nonlinear optical (NLO) candidates in the IR region. Moreover, band structures and NLO properties of title compounds are also theoretically studied, and the calculated NLO coefficients are consistent with the experimental observations

Solid–Liquid Phase Equilibrium of Isophthalonitrile in 16 Solvents from <i>T</i> = 273.15 to 324.75 K and Mixing Properties of Solutions

The solid–liquid equilibrium of isophthalonitrile (IPN) in 16 solvents (methanol, ethanol, n-propanol, isopropanol, acetone, ethyl acetate, acetonitrile, chloroform, cyclohexanone, cyclopentanone, methyl acetate, ethyl formate, 2-pentanone, tetrahydrofuran, toluene, and diethyl ether) was measured by using a static equilibrium method at temperatures T = 273.15–324.75 K under atmospheric pressure. The results demonstrated that the solubility of IPN in these 16 monosolvents increased with increasing temperature. The largest solubility values of IPN were found in cyclopentanone, and the lowest were in isopropanol. The values of solubility in ketones were much larger than those in esters and alcohols. In alcohols, the solubility ranked as methanol > ethanol > n-propanol > isopropanol, and the sequence was identical to that of the solvent polarities. The polarity of the solvent is an important factor influencing the solubility profiles of IPN in alcohols, despite that the conclusion is not supported by other kinds of solvents studied. Moreover, the Apelblat equation, λh equation, Wilson model, and nonrandom two-liquid model were used to correlate the experimental values. The calculated values of four models all provided good fitting results with the experimental data, and the values of root-mean-square deviation and relative average deviation (RAD) were no more than 6.84 × 10–4 and 6.84 × 10–3, respectively. Furthermore, the thermodynamic properties of the mixing process for IPN in selected solvents were calculated, that is, mixing Gibbs energy (ΔmixG), molar enthalpy (ΔmixH), and molar entropy (ΔmixS). The results indicated that the mixing process of IPN was a spontaneous and entropy-driven process. The solid–liquid equilibrium data and solution thermodynamics would be helpful for the synthesis and purification of IPN in the industry

Infrared Nonlinear Optical Polymorphs α- and β‑SrCu₂SnS₄ Exhibiting Large Second Harmonic Generation Responses with Requisite Phase-Matching Behavior

α- and β-SrCu2SnS4 polymorphs, exhibiting special structural changes and excellent physicochemical performances, were successfully synthesized and characterized as promising IR NLO candidates. Note that they satisfy the essential phase-matching condition and have strong SHG responses about 0.7 and 1.0 times those of benchmark AgGaS2 under 2.09 μm incident light, respectively, which agree well with the theoretical SHG coefficients and suitable birefringences based on first-principles calculation. Moreover, it is also verified that their SHG effects originate from the synergetic contribution between CuS4 and SnS4 ligands after the SHG density calculations

Synthesis and Characterization of Mid-Infrared Transparency Compounds: Acentric BaHgS₂ and Centric Ba₈Hg₄S₅Se₇

Two mid-IR transparency compounds, namely, acentric BaHgS₂ (BHS) and centric Ba₈Hg₄S₅Se₇ (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic <i>Pmc</i>2₁ with [HgS₄] tetrahedra and isolated dumbbell-shaped [HgS₂] units, while BHSSe belongs to the orthorhombic space group <i>Pnma</i> with infinite isolated _∞[HgSe₂(S/Se)₂]^4– chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ∼6.5 times compared with that of reference AgGaS₂ at a fundamental wavelength (2.09 μm). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation