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Previous study suggested that Se-site doping with Te or S in tetragonal FeSe adjusts the superconductivity only by expanding or compressing the lattice parameters. However, three chalcogens X ( X = S, Se, Te) show different electronegativity, which could directly change the interaction between Fe & X , and their electronic structures. In order to understand this underlying mechanism, the samples with different anion compositions but the same lattice parameters are required. In this work, two superconductors: FeSe 0.95 Te 0.03 S 0.02 and FeSe 0.9 Te 0.057 S 0.043 have been synthesized by solid state reaction. The thus-obtained samples have the same lattice parameters in tetragonal single phase as that of undoped FeSe. It is found that despite the unchanged lattice, S/Te co-doping on Se-site still increased the density of the electronic states (DOS) near the Fermi level, thereby enhanced the superconductivity. Our results suggest that the influence of Se-site doping with the same valence chalcogen in superconducting FeSe is not simply in the view of the lattice size, effects on electronic structures originated from different electronegativity during Se-site doping should also be considered. [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]

The materials with quasi-one-dimensional crystal structure have gained intense interest because of their novel structure and related properties such as electron correlations, charge-density wave and potential superconductivity. Here we report two new Ni-based quasi-one-dimensional selenides: Rb 0.9 Ni 3.1 Se 3 and K 0.7 Ni 3.1 Se 3. These two compounds are nonstoichiometric and composed of one-dimensional (Ni 3 Se 3) ∞ infinite chains with face-sharing Ni 6 octahedra along the c direction. It is found that the interchain distance in these compounds is strongly influenced by the radius of intercalated alkali-metal cations, while the configuration of (Ni 3 Se 3) ∞ chains is basically unaffected. The conductivity measurement indicates the metallic behavior of Rb 0.9 Ni 3.1 Se 3 and K 0.7 Ni 3.1 Se 3. Meanwhile, the magnetic susceptibility reveals the spin-glass state below 10 K. It is indicated that the magnetic moments in these compounds are related to the Ni Ni bonding distance. First-principles calculation reproduces the metallic state of this 133 phase, and also suggests that the magnetic interaction is attributed to the extra Ni in structure. These compounds form a Ni-based quasi-one-dimensional material family, which provides new platform to understand the structure-property relationship of quasi-one-dimensional materials, and also offer a series of potential precursors to synthesis the novel (Ni 3 Se 3) ∞ molecular wires. Image 1 • Two new quasi-one-dimensional Ni selenides were synthesized. • They contain novel (Ni 3 Se 3) ∞ double-walled chains with face-sharing Ni 6 octahedra inside. • These two compounds show the metallic behavior. • The spin-glass state was observed below 10 K. [ABSTRACT FROM AUTHOR]

Pavonite homologues are semiconductors that show potential for thermoelectric applications. Herein, we report the synthesis of a quaternary selenide, In 0.5 Mn 2 Bi 3.5 Se 8 , that exhibits good thermal stability below 1032 K. Whereas most pavonite compounds exhibit the metallic properties of degenerate semiconductors, In 0.45 Mn 2.17 Bi 3.38 Se 8 possesses a band gap of 0.85 eV. In addition, its electrical conductivity and Seebeck coefficient exceed 3 S/cm and 300 μV/K at 810 K, respectively, with the compound mainly displaying semiconductor properties. In 0.45 Mn 2.17 Bi 3.38 Se 8 exhibits paramagnetism at room temperature followed by a paramagnetic-to-antiferromagnetic transition at ∼10.2 K. Our findings enrich the current understanding of the pavonite homologous series, providing useful insight for future exploration in related fields. • A homologue of pavonite series with N = 3 showed good thermal stability. • The conductivity to exhibit semiconducting behavior at high temperatures. • Low thermal conductivity can be observed over the entire temperature range. • At ∼10.2 K, the compound underwent an antiferromagnetic transition. [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]