- Three new phases in the K/Cu/Th/S system: KCuThS3, K 2Cu2ThS4, and K3Cu 3Th2S7
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Synthetic exploration of K/Cu/Th/S quaternary phase space has yielded three new compounds: KCuThS3 (I), K2Cu2ThS 4 (II), and K3Cu3Th2S7 (III). All three phases are semiconductors with optical band gaps of 2.95, 2.17, and 2.49 eV(I-III). Compound I crystallizes in the orthorhombic space group Cmcm with a = 4.076(1) A, b = 13.864-(4) A, and c = 10.541(3) A. Compound II crystallizes in the monoclinic space group C2/m with a = 14.522(1) A, b = 4.026(3) A, and c = 7.566(6) A; β = 109.949(1)°. Compound III crystallizes in orthorhombic space group Pbcn with a = 4.051(2) A, b = 14.023(8) A, and c = 24.633(13) A. The compounds are all layered materials, with each layer composed of threads of edge-sharing ThS6 octahedra bridged by CuS4 tetrahedral threads of varying dimension. The layers are separated by well-ordered potassium ions. The relatively wide range of optical band gaps is attributed to the extent of the CuS4 motifs. As the dimension of the CuS4 chains increases, band gaps decrease in the series. All materials were characterized by single-crystal X-ray diffraction, microprobe chemical analysis, and diffuse reflectance spectroscopy (NIR-UV).
- Selby, Hugh D.,Chan, Benny C.,Hess, Ryan F.,Abney, Kent D.,Dorhout, Peter K.
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- Structural frustration and occupational disorder: The rare earth metal polysulfides Tb8S14.8, Dy8S14.9, Ho8S14.9, and Y8S14.8
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Dark red crystals of Y8S14.8, Tb8S 14.8, Dy8S14.9, and Ho8S 14.9 have been obtained following different reaction routes. The isostructural title compounds adopt the Gd8Se15 type, a 24-fold superstructure of the ZrSSi-type and can be described in space group A112 (non standard setting of C121, no. 5) with lattice parameter of a = 11.505(1) A, b = 15.385(1) A, c = 15.726(1) A, and γ = 90.21(2)° for Y8S15-x; a = 11.660(1) A, b = 15.468(2) A, c = 15.844(2) A, and γ = 90.19(2)° for Tb8S15-x; a = 11.584(1) A, b = 15.340(2) A, c = 15.789(2) A, and γ = 90.34(2)° for Dy8S 15-x; and a = 11.538(1) A, b = 15.288(2) A, c = 15.740(2) A, and γ = 90.23(1)° for Ho8S15-x, respectively. The structure consists of an alternating stacking of puckered [RES] (RE, rare-earth metals) double slabs and planar sulfur layers along [001]. The planar sulfur layers have a complex arrangement of S2 2- dinuclear dianions, isolated S2- ions, and vacancies. All compounds contain trivalent rare-earth metal ions, for Tb8S 15-x and Dy8S15-x antiferromagnetic order was found at TN = 5.4(2) K and 3.8(1) K, respectively. Short wavelength cutoff optical band gaps of 1.6 to 1.7 eV were determined.
- Doert, Thomas,Graf, Christian,Vasilyeva, Inga G.,Schnelle, Walter
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- Synthesis, structure, and optical properties of K2.4Ga2.4M1.6Q8 (M = Si, Ge; Q = S, Se) crystals and glasses
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Four new compounds, K2.4Ga2.4M1.6Q8 (M = Si, Ge; Q = S, Se), were successfully synthesized via a reactive flux method. All compounds crystallize in the tetragonal system of space group I4/mcm, and belong to the Tl2Se2 structure type (Pearson symbol tI16). The isostructural scaffold of the compounds feature [(Ga0.6/M0.4)Q4/2] one-dimensional chains separated by K+ ions. The chains are composed of edge-sharing [(Ga0.6/M0.4)Q4/2] tetrahedrons. Powder and glass samples were synthesized from solid state reactions with different annealing processes. The transport properties of crystalline K2.4Ga2.4Ge1.6S8 and K2.4Ga2.4Ge1.6Se8 were determined from optical absorption measurements to be wide band gap semiconductors (Eg = 3.5 eV for K2.4Ga2.4Ge1.6S8 and 2.7 eV for K2.4Ga2.4Ge1.6Se8). A red shift of the band gap energy in the glass samples was observed. K2.4Ga2.4Ge1.6S8 glass showed a wide transparent range from 0.6 μm to 10 μm and a high soften-temperature of 533 °C. First-principles calculations fitted well with the optical measurements, indicating that the Ge substitution is beneficial for narrowing the band gap.
- He, Jianqiao,Zhang, Xian,Guo, Pan,Cheng, Ye,Zheng, Chong,Huang, Fuqiang
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p. 76789 - 76794
(2016/08/30)
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- Highly efficient iodine capture by layered double hydroxides intercalated with polysulfides
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We demonstrate strong iodine (I2) vapor adsorption using Mg/Al layered double hydroxide (MgAl-LDH) nanocomposites intercalated with polysulfide (Sx2-) groups (Sx-LDH, x = 2, 4, 6). The as-prepared LDH/polysulfide hybrid materials display highly efficient iodine capture resulting from the reducing property of the intercalated polysulfides. During adsorption, the I2 molecules are reduced to I3- anions by the intercalated [Sx]2- groups that simultaneously are oxidized to form S8. In addition to the chemical adsorption, additional molecular I2 is physically captured by the LDH composites. As a result of these parallel processes, and despite their very low BET surface areas, the iodine capture capacities of S2-LDH, S4-LDH, and S6-LDH are 1.32, 1.52, and 1.43 g/g, respectively, with a maximum adsorption of 152% (wt %). Thermogravimetric and differential thermal analysis (TG-DTA), energy dispersive X-ray spectroscopy (EDS), and temperature-variable powder X-ray diffraction (XRD) measurements show the resulting I3- ions that intercalated into the LDH gallery have high thermal stability (¥350 °C). The excellent iodine adsorption performance combined with the facile preparation points to the Sx-LDH systems as potential superior materials for adsorption of radioactive iodine, a waste product of the nuclear power industry.
- Ma, Shulan,Islam, Saiful M.,Shim, Yurina,Gu, Qingyang,Wang, Pengli,Li, Hao,Sun, Genban,Yang, Xiaojing,Kanatzidis, Mercouri G.
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p. 7114 - 7123
(2015/02/19)
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- Energetics of a zinc-sulfur fuel cell
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Energetics of a novel zinc-sulfur charge storage (generalized as Zn + S a?? ZnS) is explored to access the high (> 1000 Ah/kg) charge capacity of sulfur. At 25 ?°C, the theoretical energy density of the complete Zn/S system is a high 572 Wh/kg, at E?
- Bendikov, Tatyana A.,Yarnitzky, Chaim,Licht, Stuart
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p. 2989 - 2995
(2007/10/03)
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- Polysulfide anions. 1. Structure and vibrational spectra of the S22- and S32- anions. Influence of the cations on bond length and angle
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In a comprehensive study of the M2Sn and M′Sn alkali (M) and alkaline-earth (M′) polysulfides, the alkali polysulfides K2S2, Na2S3·NH3, and K22S3 have been prepared by reaction of the metal with sulfur in liquid ammonia and subsequent heat treatments. Their Raman spectra have been analyzed in relation to their known X-ray structures, and that of BaS3 has been revisited. The structure of K2S2 seems intermediate in the M2S2, M′S2 series since it has two slightly different anions in the unit cell. As for Na2S2, K2S2 has two α and β phases but with a much higher transition temperature ~310°C. These results, and those of the literature, allow the S22- bond length to be related to the variation of its electronic structure with the cation electric field. The results obtained for the M2S3 and M′S3 polysulfides, and those of the literature, show the existence of a low- and a high-temperature phase for K2S3 as for the other M2S3 compounds. The S32- anion geometry, as for S22-, is directly related to the cation electric field. The opening of the SSS angle in BaS3 is linked to the absence of cations at short distance of both terminal sulfur atoms of the S32- anion. It is thus shown that the bond length decreases with the polarizing power of the cations. The force field calculated for these anions are related to the SS bond length. The phase transformations and the stability of these compounds is explained by the polarizing power of the cation, which drives the volume left free for the anion in the crystal.
- Jaroudi, Omar El,Picquenard, Eric,Demortier, Antoine,Lelieur, Jean-Pierre,Corset, Jacques
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p. 2394 - 2401
(2008/10/08)
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- KINETICS AND MACROKINETICS OF THE HIGH-TEMPERATURE REDUCTION OF POTASSIUM SULFATE BY HYDROGEN. I. EXPERIMENTAL RESULTS AND REACTION MECHANISM.
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A study was carried out on the kinetics of the heterogeneous reduction of potassium sulfate (50 mu m mean paraticle size) by hydrogen at 1033-1073 degree K in a quartz flow reactor at atmospheric pressure. Measurements were carried out for the temperatures of the gas flow and sample and the condensed phase and exit gases were subjected to chemical analysis. The reduction products are liquid potassium sulfide, potassium polysulfides, and potassium hydroxide and gaseous water and hydrogen sulfide. Two mechanistic variants were proposed for the reduction of potassium sulfate by hydrogen.
- Ibragimiov,Zyryanov,Mostinskii,Rozovskii
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p. 1255 - 1260
(2008/10/08)
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