Crystal chemistry of oxide–chalcogenides. II. Synthesis and crystal structure of the first bismuth oxide–sulfide, Bi2O2S

Structural Diversity of Rare-Earth Oxychalcogenides

Mixed-anion systems have garnered much attention in the past decade with attractive properties for diverse applications such as energy conversion, electronics, and catalysis. The discovery of new materials through mixed-cation and single-anion systems proved highly successful in the previous century, but solid-state chemists are now embracing an exciting design opportunity by incorporating multiple anions in compounds such as oxychalcogenides. Materials containing rare-earth ions are arguably a cornerstone of modern technology, and herein, we review recent advances in rare-earth oxychalcogenides. We discuss ternary rare-earth oxychalcogenides whose layered structures illustrate the characters and bonding preferences of oxide and chalcogenide anions. We then review quaternary compounds which combine anionic and cationic design strategies toward materials discovery and describe their structural diversity. Finally, we emphasize the progression from layered two-dimensional compounds to three-dimensional networks and the unique synthetic approaches which enable this advancement.

Metal Oxysulfides: From Bulk Compounds to Nanomaterials

This review summarizes the syntheses and applications of metal oxysulfides. Bulk compounds of rare earth and transition metals are discussed in the section Introduction. After a presentation of their main properties and applications, their structures are presented and their syntheses are discussed. The section Bulk Materials and Their Main Applications is dedicated to the growing field of nanoscaled metal oxysulfides. Synthesis and applications of lanthanide-based nanoparticles are more mature and are discussed first. Then, works on transition-metal based nanoparticles are presented and discussed. Altogether, this review highlights the opportunities offered by metal oxysulfides for application in a range of technological fields, in relation with the most advanced synthetic routes and characterization techniques.

Band Gap Tuning in Bismuth Oxide Carbodiimide Bi2O2NCN

Layered bismuth oxides exhibit a broad range of tunable physical properties as a result of their excellent structural versatility which facilitates compositional substitutions at both cationic and anionic positions. Here we expand this family in a new direction through the preparation of the first example of a bismuth-containing oxide carbodiimide, Bi₂O₂NCN, which assumes an extended variant of the anti-ThCr₂Si₂ structure-type adopted by Bi₂O₂ Ch ( Ch = Se or Te) oxide chalcogenides. Electronic structure calculations reveal the title compound to be an indirect band gap semiconductor with a band gap of approximately 1.4 eV, in good agreement with the measured value of 1.8 eV, and intermediate between that of structurally related Bi₂O₂S (1.12 eV) and β-Bi₂O₃ (2.48 eV). Mott-Schottky experiments demonstrate Bi₂O₂NCN to be an n-type semiconductor with a conduction band edge position of -0.37 V vs reversible hydrogen electrode. This study highlights the pseudochalcogenide nature of the ^-N═C═N^- carbodiimide anion, which may be substituted in place of oxide or chalcogenide anions in this and potentially other structural classes as an effective means of electronic tuning.

One-Pot Synthesis of BiCuSO Nanosheets under Ambient Atmosphere as Broadband Spectrum Photocatalyst

Cuprous based chalcogenides have attracted intensive research interest due to the potential applications in solar energy conversion. However, typical fabrications of these compounds are often carried out under severe conditions, such as inert gas protection, high vacuum, and/or extreme high temperature. Here we reported a one-pot process for cuprous based chalcogenides synthesis in aqueous solution. A strategy for BiCuSO nanosheets fabrication without toxic chemicals or rigorous reagents at pretty low temperatures under an ambient atmosphere was established, with the practicality of morphology controlling and the compatibility of multifarious precursors. Platelike BiCuSO with a thickness range from several to hundreds nanometers are fabricated by adjusting the alkali concentration, reaction time, and temperature. The positive effect of alkali hydroxide concentration is proposed cautiously based on the experimental results. The photocatalytic activities of BiCuSO nanosheet under UV, visible, and near-infrared irradiation were also investigated. BiCuSO obtained at room temperature with a thickness of 4.5 nm showed the most impressive efficiency to decompose organic contaminants. Our research presented a new way for cuprous sulfides fabrication, and might open up a new vista for large-scale synthesis of cuprous based materials as promising broadband spectrum light-absorbing materials.

Infrared and Raman spectra of Bi2O2X and Bi2OX2 (X = S, Se, and Te) studied from first principles calculations

Crystal structures of bismuth oxychalcogenide compounds Bi₂O₂X and Bi₂OX₂ (X = S, Se, and Te).

Bismuth oxysulfide film electrodes with giant incident photon-to-current conversion efficiency: the dynamics of properties with deposition time

The dynamics of the properties of bismuth oxysulfide films has been investigated, e.g. a red shift of the absorption edge with the film thickness.

Giant Incident Photon-to-Current Conversion with Photoconductivity Gain on Nanostructured Bismuth Oxysulfide Photoelectrodes under Visible-Light Illumination

Nanostructured layered bismuth oxysulfide films synthesized by chemical bath deposition reveal a giant incident photon-to-current conversion efficiency (IPCE). This study shows that surprisingly for the cathodic photocurrent in the photoreduction process, the IPCE reaches ≈2500% in aqueous solutions containing [Fe(CN)₆ ]^3- . The giant IPCE is observed starting from a certain minimal oxidizer concentration (c > 10^-3 m for [Fe(CN)₆ ]^3- ) and decreases nonlinearly with an increase of illumination intensity. Giant IPCE is determined by the decrease in resistivity of the bismuth oxysulfide film under illumination with photoconductivity gain, which provides the possibility of charge carriers from an external circuit to participate in the photoreduction process. Giant IPCE is observed not only in [Fe(CN)₆ ]^3- solutions, but also in electrolytes containing other photoelectron acceptors: Fe³⁺ , I₃^- , quinone, H₂ O₂ . In all, solution-processed layered bismuth oxysulfide films offer large-area coverage, nontoxicity, low cost, and compatibility with a wide range of substrates. Abnormally high photoelectrochemical activity, as well as a band gap energy value favorable for efficient conversion of solar light (1.38 eV, direct optical transitions), proves the potential of bismuth oxysulfide photoelectrodes for a new generation of high-performance photoconverters.

Synthesis and characterization Bi2O2S thin film via chemical bath deposition at low pH

Bismuth oxysulfide thin film was prepared using Bi(NO3)3 and Na2S as reactive. Since bismuth in the form of bismuth oxide is dissolved into water, bismuth and sulfide concentration of the chemical bath is very important. Bismuth oxysulfide (Bi2O2S) thin films were produced below pH2. Tested bismuth and sulfide concentrations are as follows: 2×10(-1)M, 2×10(-2)M, 2×10(-3)M, 2×10(-4)M bismuth and 1×10(-1)M, 1×10(-2)M, 1×10(-3)M, 1×10(-4)M sulfide. The structure of the films was examined via X-ray diffraction (XRD). Optical properties, such as transmission and absorbance were measured with Ultra violet-visible spectrum, and then refractive index and reflectivity were calculated. The pH of chemical bath was stabilized below pH of 2 using 13.85mL concentrated nitric acid. Deposition time and temperature of the baths were 4h and 30°C. It has been found that bismuth and sulfide concentrations affected the structure and thickness of the film. Also, optical band gap of the films varied with concentration, parallel to the change of the structure and film thickness.

Fully Understanding the Photochemical Properties of Bi2O2(CO3)1-xSx Nanosheets

The photochemical properties of crystal facets with obviously distinct atomic and geometric structures have been studied widely to date. However, little work has been performed for two or more facets with very similar atomic and geometric structures. Herein, we mainly report the photochemical properties of {001} and {100} facets of Bi2O2(CO3)1-xSx with very similar atomic and geometric structures. The simulation and experimental results show that over {100} facets, sulfur prefers to substitute for the carbonate anion, leading to the formation of an interesting serpentine internal electric field that greatly inhibits the charge recombining of electrons and holes, which has rarely been demonstrated; over {001} facets, however, sulfur preferentially adsorbs in oxygen vacancies, which greatly reduces the surface energy of {001} facets, leading to 80% of the high-energy {001} facets exposed. As a result, the photochemical properties of nanosheets have been greatly improved. This study could help us to fully understand the photochemical properties of semiconductors.

Thermal decomposition of bismuth oxysulfide from photoelectric Bi2O2S to superconducting Bi4O4S3

With the addition of oxygen into the chain-like bismuth sulfide of Bi2S3, there are two interesting functional compounds of Bi2O2S (photoelectric) and Bi4O4S3 (superconducting) containing the PbO-like [Bi2O2] layers. Nanoscale Bi2O2S crystals with an indirect band gap of 1.12 eV are synthesized via a facile hydrothermal method. This semiconductor shows excellent photoelectric response under the irradiation of visible light lamp at room temperature. Theoretical calculations and packing factor model both indicate that the loosely packed Bi2O2S is an excellent photoelectric material. When the Bi2O2S phase was annealed at 500 °C in an evacuated quartz tube, nanocrystals of Bi4O4S3 were obtained. The powder X-ray diffraction and electron microscope analyses (SEM, TEM, EDX) confirmed the thermal decomposition from orthorhombic Bi2O2S to tetragonal Bi4O4S3. The superconducting transition temperature of Bi4O4S3 was observed to be 4.6 K from the temperature-dependence measurements of electrical resistivity and magnetic susceptibility. Our results also provide a new method utilizing thermal decomposition to prepare a new phase without high temperature reaction.

Synthesis, characterisation and properties of rare earth oxyselenides A4O4Se3(A = Eu, Gd, Tb, Dy, Ho, Er, Yb and Y)

We report the synthesis of new A₄O₄Se₃(A = rare earth element) materials and identify three new structure types (β, γ, δ).

Stacking variants and superconductivity in the Bi-O-S system

High-temperature superconductivity has a range of applications from sensors to energy distribution. Recent reports of this phenomenon in compounds containing electronically active BiS2 layers have the potential to open a new chapter in the field of superconductivity. Here we report the identification and basic properties of two new ternary Bi-O-S compounds, Bi2OS2 and Bi3O2S3. The former is non-superconducting; the latter likely explains the superconductivity at T(c) = 4.5 K previously reported in "Bi4O4S3". The superconductivity of Bi3O2S3 is found to be sensitive to the number of Bi2OS2-like stacking faults; fewer faults correlate with increases in the Meissner shielding fractions and T(c). Elucidation of the electronic consequences of these stacking faults may be key to the understanding of electronic conductivity and superconductivity which occurs in a nominally valence-precise compound.

Vertex-Linked ZnO2S2 Tetrahedra in the Oxysulfide BaZnOS: a New Coordination Environment for Zinc in a Condensed Solid

The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) angstroms, b = 12.8541(7) angstroms, c = 6.1175(4) angstroms, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible.