Homologous Series of 2D Chalcogenides Cs–Ag–Bi–Q (Q = S, Se) with Ion-Exchange Properties

Phase Discovery and Selected Synthesis of Subvalent Niobium Tellurides Using a Polytelluride Flux Strategy

Transition metal subchalcogenides involve electron-rich metals and can facilitate an in-depth understanding of the relationships among quantum properties such as superconductivity, charge density wave, and topological band structures. However, effective experimental routes toward synthesizing transition metal subchalcogenides are still lacking, hindering the development of new quantum materials. Herein, we propose a eutectic polytelluride flux strategy as an excellent solution to address phase discovery and crystal growth in transition metal subtelluride systems. We report new phases easily and selectively synthesized using a eutectic "K₃Te₄" polytelluride flux upon adjusting the ratio of Nb metal to flux in the starting materials (K/Nb/Te = 3:x:4). Using a high Nb content in the solvent (x = 2 and 1), crystals of KNb₃Te₃O_0.38 and K_0.9Nb₃Te₄ are obtained. Both subtellurides exhibit diverse Nb clusters, including face-sharing and edge-sharing Nb₆ octahedral columns and zig-zag Nb chains. Reducing the Nb content to x = 0.33 leads to the formation of a layered compound, K_1.06NbTe₂. This compound comprises a NbTe₆ trigonal prism with K intercalated between the layers. Single crystals of known binary Nb tellurides can also be grown using another eutectic flux "KTe_3.2", and the obtained NbTe₂ exhibits a new polymorphism with extra trimerization along the b-axis in the Nb-Nb bonded double zig-zag cluster. Precise control over the structural dimensionality and oxidation state, combined with the facile crystal growth process, makes our synthetic strategy an efficient route to explore quantum materials in transition metal subchalcogenides.

Highly selective cesium removal under acidic and alkaline conditions using a novel potassium aluminum thiostannate

The pH values of nuclear wastewater are extremely low or high, which make the efficient removal of ¹³⁷Cs a major concern among the issues for safety management and environmental remediation. Existing metal sulfides for Cs⁺ adsorption have shown poor performance at acidic and alkaline conditions, and the reason has not been revealed yet. Herein, a novel potassium aluminum thiostannate (KAlSnS-3) adsorbent was designed and its Cs⁺ adsorption mechanism over a wide pH range was investigated. We hypothesized that Al³⁺ dopant on Sn⁴⁺ sites would allow stable adsorption for Cs⁺ upon its partial release at acidic and alkaline conditions. As a result, KAlSnS-3 demonstrated excellent adsorption performance across a broad pH range (1-13), and high selectivity toward Cs⁺, even under high salinity conditions (in tap water K_d = 3.12 × 10⁴ mL/g; and in artificial seawater K_d = 3.42 × 10³ mL/g). KAlSnS-3 also exhibited rapid adsorption kinetics (R = 97.6% in the first minute), a remarkable adsorption capacity (259.31 mg/g), and a high distribution coefficient (2.09 × 10⁵ mL/g) toward Cs⁺. In addition, the high reusability of KAlSnS-3 was observed, suggesting its potential for real-world applications. The mechanism for enhancing performance at low and high pH values was discussed with the evidence of crystallinity, elemental concentrations, and binding energy of electrons based on the concept of electrostatic interactions and chemical affinity. In summary, this work provides insights into the mechanism of Cs⁺ removal under a wide pH range, and the impressive Cs⁺ adsorption performance indicates the application potential of KAlSnS-3 in wastewater treatment.

2D Homologous Series SrFMnBiSn+2 (M = Pb, Ag0.5Bi0.5; n = 0, 1) and Commensurately Modulated Sr2F2Bi2/3S2

We report three new mixed-anion two-dimensional (2D) compounds: SrFPbBiS₃, SrFAg_0.5Bi_1.5S₃, and Sr₂F₂Bi_2/3S₂. Their structures as well as the parent compound SrFBiS₂ were refined using single-crystal X-ray diffraction data, with the sequence of SrFBiS₂, SrFPbBiS₃, and SrFAg_0.5Bi_1.5S₃ defining the new homologous series SrFM_nBiS_n+2 (M = Pb, Ag_0.5Bi_0.5; n = 0, 1). Sr₂F₂Bi_2/3S₂ has a different structure, which is modulated with a q vector of 1/3b* and was refined in superspace group X2/m(0β0)00 as well as in the 1 × 3 × 1 superstructure with space group C2/m (with similar results). Sr₂F₂Bi_2/3S₂ features hexagonal layers of alternating [Sr₂F₂]²⁺ and [Bi_2/3S₂]^2-, and the modulated structure arises from the unique ordering pattern of Sr²⁺ cations. SrFPbBiS₃, SrFAg_0.5Bi_1.5S₃, and Sr₂F₂Bi_2/3S₂ are semiconductors with band gaps of 1.31, 1.21, and 1.85 eV, respectively. The latter compound exhibits room temperature red photoluminescence at ∼700 nm.

Syntheses and characterization of two new layered ternary chalcogenides NaScQ2 (Q = Se and Te)

Two new metal ternary chalcogenides, NaScSe2 and NaScTe2, have been synthesized via high-temperature reaction.

Syntheses of five new layered quaternary chalcogenides SrScCuSe3, SrScCuTe3, BaScCuSe3, BaScCuTe3, and BaScAgTe3: crystal structures, thermoelectric properties, and electronic structures

Five new layered transition metal-based chalcogenides (SrScCuSe3, SrScCuTe3, BaScCuSe3, BaScCuTe3, and BaScAgTe3) were discovered by the exploratory solid-state method.

Non-centrosymmetric sulfides A2Ba6MnSn4S16 (A = Li, Ag): syntheses, structures and properties

Li₂Ba₆MnSn₄S₁₆ and Ag₂Ba₆MnSn₄S₁₆ are synthesized for the first time. By modulating disordered sites with Mn²⁺, they not only show strong SHG responses and wide band gaps (5.1, 2.7 × AgGaS₂; 2.88, 2.76 eV), but also possess paramagnetism.

Thermoelectric Material SnPb2Bi2S6: The 4,4L Member of Lillianite Homologous Series with Low Lattice Thermal Conductivity

Although the binary sulfides Bi₂S₃, PbS, and SnS have attracted extensive interest as thermoelectric materials, no quaternary sulfides containing Sn/Pb/Bi/S elements have been reported. Herein, we report the synthesis of a new quaternary sulfide, SnPb₂Bi₂S₆, which crystallizes in the orthorhombic space group Pnma with unit cell parameters of a = 20.5458(12) Å, b = 4.0925(4) Å, c = 13.3219(10) Å. SnPb₂Bi₂S₆ has a lillianite-type crystal structure consisting of two alternately aligned NaCl-type structural motifs separated by a mirror plane of PbS₇ monocapped trigonal prisms. In the lillianite homologous series, SnPb₂Bi₂S₆ can be classified as ^4,4L, where the superscripted numbers indicate the maximum numbers of edge-sharing octahedra in the two adjacent NaCl-shaped slabs along the diagonal direction. The obtained SnPb₂Bi₂S₆ phase exhibited good thermal stability up to 1000 K and n-type degenerate semiconducting behavior, with a power factor of 3.7 μW cm^-1 K^-2 at 773 K. Notably, this compound exhibited a very low lattice thermal conductivity of 0.69-0.92 W m^-1 K^-1 at 300-1000 K. Theoretical calculations revealed that the low thermal conductivity is caused by the complex crystal structure and the related elastic properties of a low Debye temperature, low phonon velocity, and large Grüneisen parameters. A reasonable figure of merit (ZT) of ∼0.3 was obtained at 770 K.

BaMnSnS4 and BaCdGeS4: infrared nonlinear optical sulfides containing highly distorted motifs with centers of moderate electronegativity

IR NLO sulfides BaMnSnS₄ and BaCdGeS₄ exhibit significant SHG efficiencies (1.2 and 0.3AgGaS₂) with phase-matching behavior and high laser-induced damage thresholds (10 and 13AgGaS₂).

Two Mercury Antimony Chalcogenides Cs2HgSb4S8 and Cs2Hg2Sb2Se6 with Cesium Cations as Counterions

Two novel layer structure compounds, Cs₂HgSb₄S₈ and Cs₂Hg₂Sb₂Se₆, were synthesized in organic solvent under solvothermal conditions. The Cs₂HgSb₄S₈ is formed of [HgSb₄S₈]^2- ribbons and S atoms by corner sharing. The Cs₂Hg₂Sb₂Se₆ is made up of [SbHg₂Se₆]^5- ribbon and disorder trigonal-pyramidal SbSe₃ by sharing μ₃-Se. These compounds are characterized by single-crystal X-ray diffraction, powder X-ray diffraction, solid-state optical absorption spectra, and so on.