Jianqiao He

Quaternary Sulfide Ba6Zn6ZrS14: Synthesis, Crystal Structure, Band Structure, and Multiband Physical Properties

Ba6Zn6ZrS14 was synthesized by a traditional salt-melt method with KI as flux. The pale yellow crystals of Ba6Zn6ZrS14 crystallize in the tetragonal space group I4/mcm with a=16.3481 (4) Å and c=9.7221(6) Å. The structure features unique one-dimensional parallel [Zn6S9](6-) and [ZrS5](6-) straight chains. The D2h-symmetric [Zn6S9](6-) cluster serves as the building block of the [Zn6S9](6-) chains. A powder sample was investigated by X-ray diffraction, optical absorption, and photoluminescence measurements. The compound shows multiple-absorption character with three optical absorption edges around 1.78, 2.50, and 2.65 eV, respectively, which are perfectly consistent with the results of first-principles calculations. Analysis of the density of states further revealed that the three optical absorption bands are attributable to the three S(3p(6))→Zr(4d(0)) transitions due to the splitting of the Zr 4d orbitals in the D4h crystal field. The multiband nature of Ba6Zn6ZrS14 also results in photocatalytic activity under visible-light irradiation and three band-edge emissions.

Synthesis, Structure, Multiband Optical, and Electrical Conductive Properties of a 3D Open Cubic Framework Based on [Cu8Sn6S24](z-) Clusters.

Two compounds with the formulas of Na4Cu32Sn12S48·4H2O and K11Cu32Sn12S48·4H2O were synthesized via flux (with thiourea as reactive flux) and hydrothermal method, respectively. The black crystals of Na4Cu32Sn12S48·4H2O and K11Cu32Sn12S48·4H2O both crystallize in the cubic space group of Fm3̅c with the cell constants a = 17.921(2) Å and a = 18.0559(6) Å, respectively. The crystal structures feature a 3D open-framework with the unique [Cu8Sn6S24](z-) (z = 13 for Na4Cu32Sn12S48·4H2O; z = 14.75 for K11Cu32Sn12S48·4H2O) clusters acting as building blocks. The [Cu8Sn6S24](z-) cluster of the Th symmetry is built up by eight [CuS3] triangles and six [SnS4] tetrahedra. The powder samples were investigated by X-ray diffraction and optical absorption measurements. Both phase-pure compounds show multiabsorption character with a main absorption edge (2.0 eV for Na4Cu32Sn12S48·4H2O and 1.9 eV for K11Cu32Sn12S48·4H2O) and an additional absorption peak (1.61 eV for Na4Cu32Sn12S48·4H2O and 1.52 eV for K11Cu32Sn12S48·4H2O), which are perfectly consistent with the first-principle calculation results. The analyses of the density of states further reveal that the two optical absorption bands in each compound are attributed to the two transitions of Cu-3d-S-3p → Sn-5s. The multiband nature of two compounds also enhances photocatalytic activity under visible light irradiation, with which the degradation of methyl blue over Na4Cu32Sn12S48·4H2O reached 100% in 3 h. The 3D open-framework features also facilitate the ionic conductivity nature of the Na4Cu32Sn12S48·4H2O compound, which achieved ∼10(-5) S/cm at room temperature.

Synthesis, crystal structure and physical properties of [Li0.85Fe0.15OH][FeS]

The layered mixed anion compound with the formula [Li0.85Fe0.15OH][FeS] was synthesized via a facile hydrothermal method. [Li0.85Fe0.15OH][FeS], which is determined by single crystal X-ray diffraction and refined by the SHELXTL program, crystallizes in the tetragonal space group of P4/nmm (a = b = 3.6886(3) A, c = 8.915(1) A, V = 121.29(2) A3, Z = 2). The structure features alternatively packed anti-PbO-like [Li0.85Fe0.15OH] and anti-PbO [FeS] layers. The sample was characterized by Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM). Powder X-ray diffraction results confirm the phase purity of the as-synthesized crystals. Temperature-dependent measurements of magnetic susceptibility reveal the presence of a paramagnetic-to-ferromagnetic phase transition around 50 K, accompanied by the metal-to-semiconductor phase transition in the temperature-dependent resistance of the [Li0.85Fe0.15OH][FeS] single crystal.

Semiconductor Pb2P2S6 and size-dependent band gap energy of its nanoparticles

Microcrystalline Pb2P2S6 powder was synthesized via a traditional melting salt method with KI or LiBr/KBr mixture (mole ratio is 3/2) acting as flux. The nanostructured Pb2P2S6 powder was further synthesized by a high-speed ball milling technique. The Pb2P2S6 powder was investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), optical absorption (UV-vis) and photoluminescence measurements. The average particle size of the nanostructured Pb2P2S6 powder changes from 500 to 60 nm when increasing the milling time from 0.5 h to 4 h. The optical properties of the Pb2P2S6 powder show a size-dependence, with the band gap ranging from 2.56 eV to 2.88 eV. First-principle calculation reveal that the Pb2P2S6 is a semiconductor with an indirect band gap of 2.15 eV. The size-dependent nature also makes the photoluminescence properties of the material tunable.

Antiperovskite Chalco-Halides Ba3(FeS4)Cl, Ba3(FeS4)Br, and Ba3(FeSe4)Br with Spin Super-Super Exchange.

Perovskite-related materials have received increasing attention for their broad applications in photovoltaic solar cells and information technology due to their unique electrical and magnetic properties. Here we report three new antiperovskite chalco-halides: Ba3(FeS4)Cl, Ba3(FeS4)Br, and Ba3(FeSe4)Br. All of them were found to be good solar light absorbers. Remarkably, although the shortest Fe-Fe distance exceeds 6 Å, an unexpected anti-ferromagnetic phase transition near 100 K was observed in their magnetic susceptibility measurement. The corresponding complex magnetic structures were resolved by neutron diffraction experiments as well as investigated by first-principles electronic structure calculations. The spin-spin coupling between two neighboring Fe atoms along the b axis, which is realized by the Fe-S···S-Fe super-super exchange mechanism, was found to be responsible for this magnetic phase transition.

Synthesis, structure, magnetic and photoelectric properties of Ln3M0.5M′Se7 (Ln = La, Ce, Sm; M = Fe, Mn; M′ = Si, Ge) and La3MnGaSe7

Six new isostructural compounds, with the formulas La3Fe0.5GeSe7, La3MnGaSe7, Ce3Fe0.5SiSe7, Ce3Mn0.5SiSe7, Sm3Fe0.5SiSe7 and Sm3Mn0.5GeSe7, have been successfully synthesized via a molten salt method. Their structures are determined by single crystal X-ray diffraction and they crystallize in the Ce6Al3.33S14 structure type (space group: P63, Pearson symbol: hP24). Pure phases of the Ce3Fe0.5SiSe7, Ce3Mn0.5SiSe7, Sm3Fe0.5SiSe7 and Sm3Mn0.5GeSe7 compounds were obtained by solid state reaction and were characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), ultraviolet-visible-infrared (UV-vis-IR) absorbance spectroscopy, and magnetization measurements. The Ce3Fe0.5SiSe7 and Ce3Mn0.5SiSe7 compounds show paramagnetic domination accompanied by antiferromagnetic contributions, while the Sm3Mn0.5GeSe7 and Sm3Fe0.5SiSe7 compounds show anti-ferromagnetic phase transitions with Neel temperatures of 13 K and 24 K, respectively. Optical measurements reveal that all of the four compounds can absorb most of visible light. These four compounds also show photoelectric properties with the photocurrent densities of 81, 1.3, 1.8 and 0.8 μA cm−2, respectively.

Nano Titanium Monoxide Crystals and Unusual Superconductivity at 11 K

Nano TiO2 is investigated intensely due to extraordinary photoelectric performances in photocatalysis, new-type solar cells, etc., but only very few synthesis and physical properties have been reported on nanostructured TiO or other low valent titanium-containing oxides. Here, a core-shell nanoparticle made of TiO core covered with a ≈5 nm shell of amorphous TiO1+x is newly constructed via a controllable reduction method to synthesize nano TiO core and subsequent soft oxidation to form the shell (TiO1+x ). The physical properties measurements of electrical transport and magnetism indicate these TiO@TiO1+x nanocrystals are a type-ІІ superconductor of a recorded Tconset = 11 K in the binary Ti-O system. This unusual superconductivity could be attributed to the interfacial effect due to the nearly linear gradient of O/Ti ratio across the outer amorphous layer. This novel synthetic method and enhanced superconductivity could open up possibilities in interface superconductivity of nanostructured composites with well-controlled interfaces.

Synthesis, Structure, and Optical Properties of Antiperovskite-Derived Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I) Chalcohalides

Six isostructural antiperovskite-derived chalcohalides, Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I), crystallizing in the space group Pnma, have been synthesized by solid-state reactions. The crystal structure features a 3D framework with the [XBa5]9+ disordered square pyramids as building blocks and [MQ3]3- units filling the interspace. [XBa5]9+ disordered square pyramids are edge-sharing along [010], derived from the fusing of the two pyramids in octahedral [XBa6]11+. Surprisingly, Ba2AsS3X (X = Cl, Br, I) show almost the same optical band gap of 2.80 eV, and Ba2AsSe3X (X = Br, I) also have a similar band gap of 2.28 eV. The optical band gap of Ba2SbS3I is 2.64 eV. First-principles calculations reveal that the optical absorption is attributed to the transitions between Q np at the valence band maximum (VBM) and M np-Q np at the conduction band minimum (CBM). These compounds also possess interesting photoluminescence properties with splitting emission peaks on excitation at 200 nm.

Synthesis, Crystal Structure, and Optical Properties of Noncentrosymmetric Na2ZnSnS4

A new chalcogenide Na2ZnSnS4 has been successfully synthesized by using Na2S2 as reactive flux. Na2ZnSnS4 crystallizes in the tetragonal system with space group of I4̅. Its cell parameters are a = 6.4835(6) Å and c = 9.134(1) Å. The structure is a derivative of AgGaS2, in which the Ag+ ions are replaced by Na+ ions and the Ga3+ ions are replaced by Zn2+ and Sn4+ ions. All three cations are in seriously distorted tetrahedral geometry with a distortion factor (η = c/ a) of 1.4. Optical measurements show that the Na2ZnSnS4 powder sample has a large transparent range from 0.8 to 25 μm and a wide band gap of 3.1 eV. It exhibits large second-harmonic generation intensity of 0.9 × AgGaS2 in the grain size range from 41 to 74 μm. First-principles calculation results reveal that the valence band maximum and conduction band minimum are mainly composed of S 3p, Zn 3d orbitals and Sn 5s, S 3p orbitals, respectively.

Effects of Iron Doping on the Physical Properties of Quaternary Ferromagnetic Sulfide: Ba2Fe0.6V1.4S6

The mixed-metal sulfide compound with the formula Ba2Fe0.6V1.4S6 was successfully synthesized via solid-state reaction. Ba2Fe0.6V1.4S6 has a quasi-one-dimensional structure and crystallizes in the hexagonal space group P63/mmc. The structure is composed of face-sharing anion octahedron [MS6]8- (M = V or Fe) units to construct infinite chains along the c axis, in which the Fe atoms randomly occupy the V sites. The Ba2+ ions reside between adjacent chains. Magnetic susceptibility measurements reveal a transition between paramagnetism and ferromagnetism around 25 K. The small polaron hopping (SPH) conduction behavior has been observed in the higher temperature region (75-300 K), while in the lower temperature region (25-74 K), the resistivity features a variable range hopping mechanism (VRH). The analysis of density of states indicates that Fe-3dz2 and S-3p states mainly dominate the valence band maximum, while Fe-3dz2 states contribute significantly to the magnetic susceptibility.