NaBa2Cu3S5: A Doped p-Type Degenerate Semiconductor

Layered NaBa2M3Q3(Q2) (M = Cu or Ag; Q = S or Se) Chalcogenides and Local Ordering in Their Mixed-Anion Compositions

Three new NaBa2M3Q3(Q2) (M = Ag or Cu; Q = S or Se) chalcogenides were prepared by using solid-state methods and structurally characterized by using single-crystal X-ray diffraction. NaBa2Ag3Se3(Se2) and NaBa2Cu3Se3(Se2) crystallize in monoclinic space group C2/m and have a two-dimensional structure composed of edge-sharing MSe4/4 tetrahedra separated by Na+ and Ba2+ cations, along with (Se2)2- dimers at the center of the spacings between [M3Se3]3- slabs. NaBa2Ag3S3(S2) adopts a related structure with space group C2/m but has additional, crystallographically distinct Ag atoms in the [Ag3S3]3- layer that are linearly coordinated. NaBa2Ag3Se3(Se2) and NaBa2Ag3S3(S2) have indirect band gaps measured to be 1.2 and 1.9 eV, respectively, which is supported by band structures calculated using density functional theory. Mixed-anion NaBa2Cu3Se5-xSx compositions were prepared to probe the presence of anion ordering and heteronuclear (S-Se)2- dimers. Structural analyses of the sulfoselenides indicate that selenium preferentially occupies the Q-Q dimer sites, while Raman spectroscopy reveals a mixture of (S2), (Se2), and heteronuclear (S-Se) units in the sulfur-rich products. The local ordering of the chalcogens is rationalized using simple bonding concepts and adds to a growing framework for understanding ordering phenomena in mixed-anion systems.

[Ba4 (S2 )][ZnGa4 S10 ]: Design of an Unprecedented Infrared Nonlinear Salt-Inclusion Chalcogenide with Disulfide-Bonds

Salt-inclusion chalcogenides (SICs) have been receiving widespread attention due to their large second harmonic generation (SHG) responses and wide bandgaps, however most of them suffer from small birefringence limiting their technical application. Herein, by introducing the π-conjugated (S2 )2- units in the ionic guest of salt-inclusion structure, the first disulfide-bond-containing SIC, [Ba4 (S2 )][ZnGa4 S10 ] has been synthesized. It exhibits the widest bandgap up to 3.39 eV among polychalcogenides and strong SHG response as large as that of AgGaS2 (AGS). Importantly, its birefringence reaches a max value of 0.053@1064 nm among AGS-like SICs, indicating it is a promising IR nonlinear optical (NLO) material. Theoretical calculations reveal that the π-conjugated (S2 )2- units and covalent GaS layers favor the enhanced birefringence and large SHG response. This work provides not only a new type of SIC for the first time, but also new lights on the design of IR NLO materials.

Synthesis and Magnetic, Optical, and Electrocatalytic Properties of High-Entropy Mixed-Metal Tungsten and Molybdenum Oxides

High-entropy oxides (HEOs) are of interest for their unique physical and chemical properties. Significant lattice distortions, strain, and tolerance for high-vacancy concentrations set HEOs apart from single-metal or mixed-metal oxides. Herein, we synthesized and characterized the structures and compositions, along with the optical, magnetic, and electrocatalytic properties, of two families of high-entropy mixed-metal tungsten and molybdenum oxides, AWO₄ and B₂Mo₃O₈, where A and B are 3d transition metals. The HEOs A⁶WO₄ (A = Mn, Fe, Co, Ni, Cu, and Zn) and B₂⁵Mo₃O₈ (B = Mn, Fe, Co, Ni, and Zn), as well as all accessible single-metal AWO₄ and B₂Mo₃O₈ parent compounds, were synthesized using high-temperature solid-state methods. X-ray photoelectron spectroscopy analysis of the surfaces revealed that the HEOs largely had the metal oxidation states expected from the bulk chemical formulas, but in some cases they were different than in the parent compounds. A⁶WO₄ exhibited antiferromagnetic (AFM) ordering with a Néel temperature of 30 K, which is less than the average of its AFM parent compounds, and had a narrow band gap of 0.24 eV, which is much lower than all of its parent compounds. B₂⁵Mo₃O₈ was paramagnetic, despite the existence of AFM and ferromagnetic ordering in several of its parent compounds and had no observable band gap, which is analogous to its parent compounds. Both A⁶WO₄ and B₂⁵Mo₃O₈ exhibited superior catalytic activity relative to the parent compounds for the oxygen evolution reaction, the oxidation half reaction of overall water splitting, under alkaline conditions, based on the overpotential required to reach the benchmark surface area normalized current density. Consistent with literature predictions of OER durability for ternary tungsten and molybdenum oxides, A⁶WO₄ and B₂⁵Mo₃O₈ also exhibited stable performance without significant dissolution during 10 h stability experiments at a constant current.

Photocurrent, humidity sensitivity and proton conductivity properties of a new sulfide semiconductor CsCuS4

Copper chalcogenides have drawn considerable attention due to their prominent semiconducting properties. A new Cu-containing semiconductor, namely, CsCuS₄ (1), was obtained by a halide salt flux method. Its structure featured 1D infinite ∞1[CuS₄] ^- chains, where the polysulfide anion S₄^2- was relatively rare in Cu chalcogenides. The compound was multifunctional and exhibited significant photocurrent, humidity sensitivity, and proton conductivity properties. Specifically, it exhibits an "on" state photocurrent response of 0.95 μA cm^-2 and an "off" state photocurrent response of 0.55 μA cm^-2 with good reversibility. The humidity-sensitive resistance in dry air (10% RH) could reach up to six orders of magnitude higher than that in wet air (100% RH). Compound 1 showed an activation energy of 0.19 eV and may have potential electrochemical applications.

Low temperature thermoelectric and magnetoresistive properties of Tl2Cu3FeQ4 (Q = S, Se, Te)

Layered Tl₂Cu₃FeSe₄ and Tl₂Cu₃FeTe₄ possess low thermal conductivity, of which the selenide offers promising thermoelectric features and the presence of Fe in the weakly connected Cu square-net substructure results in intriguing ferromagnetic and magnetoresistance features.

Ag+ insertion into 3D hierarchical rose-like Cu(1.8)Se nanocrystals with tunable band gap and morphology genetic

In this study, novel hierarchical rose-like Cu1.8Se microspheres with a porous three-dimensional (3D) framework were successfully synthesized by using a one-pot in situ growth method at low temperature (60 °C). The Cu1.8Se microspheres covered the surface of the 3D porous framework. The formation mechanism was investigated in detail by adjusting the volume ratio of DMF and EDA, as the blend solvents, and the reaction time. Then, the chemical composition of the Cu1.8Se microspheres was altered by Ag(+) exchange without changing their morphology and structure. In this way, the binary Cu1.8Se was efficiently converted into the ternary CuAgSe. Notably, the band gap of materials was tuned continuously from 3.83 eV to 3.03 eV, and CuAgSe was produced continuously by adjusting the replacement time. This work provides a novel concept and a simple method that can serve as a good reference for improving the performance of tunable materials and the preparation of multielement alloy materials.