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A one-dimensional (1D) halide double perovskite, (BA)10AgBi2Br19, is synthesized, which features 1D corner-sharing perovskite ribbons with a width of three octahedra. It is the first reported 1D derivative of a halide double perovskite, showing an unexpected narrow band gap (2.46 eV) due to the unique Br trimer in structure. [ABSTRACT FROM AUTHOR]

• Two new chalcogenides KMgCuSe 2 and KMgCuTe 2 were synthesized. • They adopt TlCr 2 Si 2 -type structure with edge-sharing tetrahedral layers separated by K+. • The band gaps are measured to be 1.26 and 1.36 eV for KMgCuSe 2 and KMgCuTe 2. • KMgCuTe 2 is paramagnetic with small effect moment as 0.31 μ B per Mg/Cu. [Display omitted] Here we report the synthesis of two new quaternary chalcogenides KMgCuSe 2 and KMgCuTe 2. Both single-crystal and polycrystalline samples have been obtained using self-flux method and high temperature reaction. These two compounds adopt ThCr 2 Si 2 -type structure which is composed of edge-sharing [Mg 0.5 Cu 0.5 Se 4 ] and [Mg 0.5 Cu 0.5 Te 4 ] tetrahedral layers separated by K+ ions. Single-crystal refinement reveals the random distribution of Mg and Cu with ratio of 1:1 in the centre of tetrahedron motifs. The Mg-Se and Mg-Te bond lengths in KMgCuSe 2 and KMgCuTe 2 are markedly shorter than those in binary MgSe and MgTe, but are comparable with the Cu-Se and Cu-Te bond lengths in binary Cu chalcogenides. In addition, the tetrahedral configurations in KMgCuSe 2 and KMgCuTe 2 are highly distorted with strong compression along c axis. These two new Mg chalcogenides are semiconductors with the indirect band gaps estimated from optical absorption spectra as 1.26 and 1.36 eV for KMgCuSe 2 and KMgCuTe 2. Magnetic susceptibility measurements indicates the paramagnetic behavior of KMgCuSe 2 and KMgCuTe 2 with small effective magnetic moment u eff (0.35 and 0.31 μ B per Mg/Cu). [ABSTRACT FROM AUTHOR]

This article reports a new perovskite compound Ca 6 Sb 2 O 11. The X-ray powder diffraction technique was used to analyze its crystal structure. The results show that Ca 6 Sb 2 O 11 has a tetragonal structure with the I 4/ m space group, and the lattice parameters are a = b = 5.658 (1) Å, c = 7.984 (1) Å, α = β = γ = 90°. It exhibits a typical A 4 B' 2 B″ 2 X 12- x anoxic multi-perovskite structure with rock-salt ordering of the B-site cations. The compound's chemical composition and valence states were characterized through scanning electron microscopy-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies was confirmed by electron paramagnetic resonance (EPR) spectroscopy. A chemical and structure transition temperature and the full melting temperature of Ca 6 Sb 2 O 11 were measured, with values of 1515 ± 3 K and 1720 ± 3 K, respectively. The density functional theory (DFT)-electron structure calculation results show that Ca 6 Sb 2 O 11 is an indirect wide-band gap (∼4.47 eV) semiconductor material, which agrees well with the experimental value (∼4.38 eV) obtained through diffuse reflection spectroscopy (DRS). Moreover, the top of the valence band and bottom of the conduction band are mainly contributed to by O-2p and Ca-3d states, respectively. The synthesis of the new perovskite compound, Ca 6 Sb 2 O 11 , requires three steps. First, the raw materials, Sb 2 O 3 and CaO, are mixed in a specific proportion. Then, the Ca 6 Sb 2 O 11 compound can be synthesized by roasting the sample at 773 K for 3 days, followed by roasting it at 1173 K for 40 days, and finally at 1586 K for 12 h. The crystal structure of the compound belongs to the tetragonal space group I 4/ m. The band structure of the compound was obtained through DFT calculation, indicating that it is an indirect bandgap semiconductor material. [Display omitted] • The new compound Ca 6 Sb 2 O 11 was synthesized and its crystal structure was analyzed. • The electronic structure of Ca 6 Sb 2 O 11 was explored by DFT calculation. • Anoxic phase Ca 6 Sb 2 O 11- x (x = 0.53) can transform into Ca 6 Sb 2 O 11 at high temperatures. [ABSTRACT FROM AUTHOR]

This paper reports the results of the photocatalytic activity of hydrogen production from water reduction using a composite catalyst of SiC/CdS with two types of heterointerfaces. Type 1 consists of hexagonal SiC and hexagonal CdS, while type 2 consists of hexagonal SiC and cubic CdS. It was found that type 1 composite exhibited an H 2 evolution rate four times greater than type 2, despite the similar bandgaps and electropotentials of both cubic and hexagonal CdS. Meanwhile, increased BET surface area, good distribution of CdS, strong light absorption and low carrier recombination were observed in type 1 heterointerface. Lattice match is thought to be achieved between two hexagonal compounds with a lattice-constant-relationship of 3 a H-CdS = 4 a H-SiC . Further, the hexagonal SiC surface (006) was shown to have an affinity with the hexagonal CdS (002) facet due to their respective polar properties. The results of this paper demonstrate that lattice match plays an important role in forming efficient heterojunctions, which in turn enhance the photocatalytic performance of composite catalysts and will prove to be helpful in designing new composite photocatalytic systems. [ABSTRACT FROM AUTHOR]

Exploring semiconductors with a large band gap and a small hole effective mass are of great importance for the development of outstanding p-type transparent conducting materials. In this work, we report the single crystal growth of two Zn-based chalcogenides K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4. Single crystal X-ray diffraction revealed that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 crystallize in P 2/ c and Ibam space group, respectively. Both compounds show layered structure, and the layers are formed by edge-sharing tetragonal [Zn 3 Q 4 ]2- units and alkali-metal cations are distributed between the layers. To our surprise, compared to the previously reported structure obtained by powder X-ray diffraction, K 2 Zn 3 S 4 crystallized in a new type of structure in which adjacent layers were displaced. Both experiments and theoretical calculations indicate that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 are direct semiconductors with large band gaps, and the experimental values are 3.6 eV for K 2 Zn 3 S 4 and 3.1 eV for Rb 2 Zn 3 Se 4. Based on first-principles calculations, the hole effective masses of K 2 Zn 3 S 4 are calculated to be as small as 0.425 me, revealing the potential remarkable transparent conductivity in this Zn-based chalcogenide. [Display omitted] • The single-crystal growth of two Zn-based chalcogenides K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4. • K 2 Zn 3 S 4 is unexpectedly found to crystallize in a new structure. • Rb 2 Zn 3 Se 4 as a new compound adopts the same structure with known Cs 2 Zn 3 Se 4. • K 2 Zn 3 S 4 exhibits both a large band gap and a small calculated hole effective mass. • Indicate the potential p-type transport conducting behavior of K 2 Zn 3 S 4. [ABSTRACT FROM AUTHOR]