Synthesis and Characterizations of Two Tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 with Flexible Chain Structure

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides β-BaGa₂Te₄ and Ba₅Ga₂Ge₃Te₁₂ have been discovered. β-BaGa₂Te₄ crystallizes in the orthorhombic space group Imma (no. 74) with unit cell constants of a = 23.813(3) Å, b = 11.9673(19) Å, and c = 6.7215(9) Å, while Ba₅Ga₂Ge₃Te₁₂ crystallizes in the monoclinic space group P2₁/c (no. 14) with unit cell constants of a = 13.6540(3) Å, b = 9.6705(2) Å, and c = 23.1134(7) Å. The structure of β-BaGa₂Te₄ can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe₂] chains formed by edge-sharing GaTe₄ tetrahedra, which are separated by Ba²⁺ cations. In the crystal structure of Ba₅Ga₂Ge₃Te₁₂, two kinds of 1D chains, namely chain 1 _∞¹[(GaGe)₃Te₈] and chain 2 _∞¹[(GaGe)₂Te₄], are stacked alternately and put together by the coulomb force with Ba²⁺ cations. In addition, First-principles calculations indicate that β-BaGa₂Te₄ has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe₄ tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.

Growth of Sb(2)E(3) (E = S, Se) polygonal tubular crystals via a novel solvent-relief-self-seeding process

A novel solvent-relief-self-seeding (SRSS) process was applied to grow bulk polygonal tubular single crystals of Sb(2)E(3) (E = S, Se), using SbCl(3) and chalcogen elements E (E = S, Se) as the raw materials at 180 degrees C for 7 days in ethanol solution. The products were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM), electronic diffraction (ED), and X-ray photoelectron spectra (XPS). The calculated electrical resistivities of the tubular single crystals in the range 20-320 K were of the order of 10(5)-10(6) Omega cm for Sb(2)S(3) and 10(3)-10(4) Omega cm for Sb(2)Se(3), respectively. The studies of the optical properties revealed that the materials formed had a band gap of 1.72 eV for Sb(2)S(3) and 1.82 eV for Sb(2)Se(3), respectively. The optimal reaction conditions for the growth of bulk tubular single crystals were that the temperature was not lower than 180 degrees C and the reaction time was not shorter than 7 days. The possible growth mechanism of tubular crystals was also discussed.

Synthesis and characterization of four new europium group XIV chalcogenides: K(2)EuTSe(5) and KEuTS(4) (T = Si, Ge)

Four europium group XIV chalcogenides have been synthesized using the reactive flux method: K(2)EuTSe(5) (I, II) and KEuTS(4) (III, IV) where T = Si, Ge. K(2)EuSiSe(5), I, crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 11.669(3) A, b = 9.844(2) A, c = 8.917(2) A, beta = 91.583(5) degrees, and Z = 4. K(2)EuGeSe(5), II, crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 11.8056(3) A, b = 9.9630(1) A, c = 8.9456(1) A, beta = 91.195(1) degrees, and Z = 4. Both K(2)EuSiSe(5) and K(2)EuGeSe(5) are semiconductors with optical band-gaps of approximately 2.00 and 1.84 eV, respectively. Raman spectroscopy shows vibrations from the (TSe(5))(4-) (T = Si, Ge) unit. KEuSiS(4), III, crystallizes in the monoclinic space group P2(1) with cell parameters a = 6.426(4) A, b = 6.582(5) A, c = 8.566(7) A, beta = 107.83(6) degrees, and Z = 2. KEuGeS(4), IV, crystallizes in the monoclinic space group P2(1) with cell parameters a = 6.510(2) A, b = 6.649(2) A, c = 8.603(3) A, beta = 107.80(2) degrees, and Z = 2. Band-gap analysis shows that both compounds are semiconductors with optical band-gaps of 1.72 and 1.71 eV, respectively. The Raman spectrum of KEuGeS(4) shows the vibrations of the (GeS(4))(4-) unit. Fluorescence spectroscopy confirms the presence of Eu(III) in III and IV instead of Eu(II) as in I and II. These four crystalline products were formed under equivalent stoichiometric reaction conditions. The fact that two different products are observed can be used to understand the relationship between the oxidative and reductive potentials within these flux reactions.

Rb(4)Hg(5)(Te(2))(2)(Te(3))(2)Te(3), [Zn(en)3](4)In(16)(Te2)4(Te3)Te22, and K2Cu2(Te2)(Te3): novel metal polytellurides with unusual metal-tellurium coordination

Three novel metal polytellurides Rb(4)Hg(5)(Te(2))(2)(Te(3))(2)Te(3) (I), [Zn(en)(3)](4)In(16)(Te(2))(4)(Te(3))Te(22) (II), and K(2)Cu(2)(Te(2))(Te(3)) (III) have been prepared by solvothermal reactions in superheated ethylenediamine at 160 degrees C. Their crystal structures have been determined by single-crystal X-ray diffraction techniques. Crystal data for I: space group Pnma, a = 9.803(2) A, b = 9.124(2) A, c = 34.714(7) A, Z = 4. Crystal data for II: space group C2/c, a = 36.814(7) A, b = 16.908(3) A, c = 25.302(5) A, beta = 128.46(3) degrees, Z = 4. Crystal data for III: space group Cmcm, a = 11.386(2) A, b = 7.756(2) A, c = 11.985(2) A, Z = 4. The crystal structure of I consists of 1D infinite ribbons of [Hg(5)(Te(2))(2)(Te(3))(2)Te(3)](4-), which are composed of tetrahedral HgTe(4) and trigonal HgTe(3) units connected through the bridging Te(2-), (Te(2))(2-), and (Te(3))(2-) ligands. II is a layered compound containing InTe(4) tetrahedra that share corners and edges via Te, Te(2), and Te(3) units to form a 2D slab that contains relatively large voids. The [Zn(en)(3)](2+) template cations are filled in these voids and between the slabs. The primary building blocks of III are CuTe(4) tetrahedra that are linked by intralayer (Te(3))(2-) and interlayer (Te(2))(2-) units to form a 3D network with open channels that are occupied by the K(+) cations. All three compounds are rare polytelluride products of solvothermal reactions that contain both Te(2) and Te(3) fragments with unusual metal-tellurium coordination.