Alkali chalcogenido ortho manganates(II) A6MnQ4 (A=Rb, Cs; Q=S, Se, Te)

2018 ◽  
Vol 73 (11) ◽  
pp. 837-848 ◽  
Author(s):  
Michael Langenmaier ◽  
Tobias Rackl ◽  
Dirk Johrendt ◽  
Caroline Röhr
Keyword(s):  
Magnetic Measurements ◽  
Magnetic Moments ◽  
Electronic Band ◽  
Chiral Structures ◽  
Pure Phase ◽  
Maximum Temperatures ◽  
Alkali Elements ◽  
Electronic Band Structures ◽  
Bonding Characteristics ◽  
Tetrahedral Voids

AbstractThe six isotypic alkali ortho chalcogenido manganates A6[MnIIQ4] (A=Rb, Cs; Q=S, Se, Te) were synthesized – in most cases in pure phase – from stoichiometric mixtures of the manganese monochalcogenides MnQ, the elemental chalcogens and Rb2S/Cs2S2 (sulfido salts) or the pure alkali elements (selenido and tellurido salts) as alkali sources at maximum temperatures between 650 and 800°C. Their hexagonal crystal structures were refined by means of X-ray single crystal data (space group P63mc, Na6ZnO4-type structure, Z=2; A/Q: Rb/S: a=1019.34(2), c=792.560(10) pm, R1=0.0166; Rb/Se: a=1055.74(2), c=821.14(2) pm, R1=0.0275; Rb/Te: a=1126.68(2), c=860.54(2) pm, R1=0.0152; Cs/S: a=1056.68(2), c=831.22(2) pm, R1=0.0168; Cs/Se: a=1096.04(3), c=858.13(2) pm, R1=0.0194; and Cs/Te: a=1167.72(3), c=896.95(2) pm, R1=0.0140). The chiral structures contain isolated C3 symmetric, but very close to ideal tetrahedral, ortho manganate(II) anions [MnIIQ4]6− with Mn–Q distances of 248.7–250.7 (Q=S), 260.7–263.0 (Q=Se) and 280.0–282.4 pm (Q=Te). The chalcogenide ions form a hexagonal closed packing with slightly puckered 36 nets, in which the A(2) cations occupy 3/4 of the octahedral interstices, whereas Mn takes 1/8 and A(1) 3/8 of the tetrahedral voids. Magnetic measurements on the three Cs compounds showed Curie-Weiss behavior down to a temperature of 1.9 K, with magnetic moments significantly reduced with respect to the expected spin-only value of a d5 ion. The electronic band structures of the four salts (Na/Rb)6Mn(S/Te)4, which were calculated within the GGA+U approach, allow a comparison of the chemical bonding characteristics and the magnetic properties within the alkali cation and the chalcogenido ligand series.

Comparatively Low Temperature Synthesis, Characterization and Some Physical Studies on Transition Metal Vanadates

2021 ◽  
Vol 13 (2) ◽  
pp. 571-578
Author(s):  
T. Vaz ◽  
A. V. Salker
Keyword(s):  
Transition Metal ◽  
Magnetic Moments ◽  
Band Gap Energy ◽  
Electronic Band ◽  
Photo Degradation ◽  
Triclinic Structure ◽  
Pure Transition ◽  
Co Precipitation ◽  
Electronic Band Structures ◽  
Bonding Characteristics

Pure transition metal vanadates NiV2O6 and CuV2O6 were successfully prepared via co-precipitation technique as low as at 600 °C. The crystal structure and their phase formation were confirmed by X-ray powdered diffraction. Both the compounds were identified to have a single-phase triclinic structure. The bonding characteristics were studied by FTIR spectroscopy. The temperature dependence of electrical resistivity of these vanadates shows a typical semiconducting nature of NiV2O6 and CuV2O6, consistent with their electronic band structures. The calculated band gap energy values of NiV2O6 and CuV2O6 were found to be 2.42 and 2.0 eV respectively, employing a DRS UV-Visible spectrophotometer. Magnetic susceptibility measurements and calculated Magnetic moments confirm their paramagnetic nature. The photocatalytic efficiency was investigated by photo-degradation of methylene blue (MB) solutions employing solar light and found to be promising photocatalysts.

THE ELECTRONIC BAND STRUCTURES FOR AN ANTIFERROMAGNETIC STATE OF Cu2Sb-TYPE INTERMETALLIC COMPOUND Cr2As

1993 ◽  
Vol 07 (01n03) ◽  
pp. 770-773 ◽  
Author(s):  
M. SHIRAI ◽  
T. KAWAMOTO ◽  
K. MOTIZUKI
Keyword(s):  
Intermetallic Compound ◽  
Electronic Band Structure ◽  
Magnetic Moments ◽  
Partial Density ◽  
Energy Splitting ◽  
Antiferromagnetic State ◽  
Good Correspondence ◽  
Electronic Band ◽  
Linearized Augmented Plane Wave ◽  
Electronic Band Structures

Electronic band structure calculations are carried out for the antiferromagnetic state of an intermetallic compound Cr2As, having the Cu2Sb-type crystal structure, by using a self-consistent linearized augmented-plane-wave (LAPW) method. The partial density of states (DOS) for Cr (II) 3d states shows a small energy splitting (about 1 eV) between the spin-up and spin-down bands, while that for Cr (I) 3d states hardly shows. The magnetic moments at Cr (I) and Cr (II) sites are evaluated to be 0.33μB and 1.37µB per atom, respectively. These values agree well with the observed values. The calculated DOS shows good correspondence with photoemission and inverse photoemission spectra measured recently.

scholarly journals Rubidium chalcogenido diferrates(III) containing dimers [Fe2Q6]6− of edge-sharing tetrahedra (Q=O, S, Se)

2017 ◽  
Vol 72 (8) ◽  
pp. 529-547 ◽  
Author(s):  
Michael Schwarz ◽  
Pirmin Stüble ◽  
Caroline Röhr
Keyword(s):  
Magnetic Moments ◽  
Magnetic Ordering ◽  
Monoclinic Space Group ◽  
Orthorhombic Space Group ◽  
Electronic Band ◽  
Space Group ◽  
Coordination Numbers ◽  
Spin Ordering ◽  
Maximum Temperatures ◽  
Type Orthorhombic

AbstractThe two isotypic rubidium chalcogenido diferrates Rb12[Fe2Q6](Q2)3 (Q=S/Se), which both form needles with green-metallic lustre, were synthesized from Rb2S, elemental iron, rubidium and sulfur (Q=S) or from the pure elements (Q=Se) at maximum temperatures of 500–800°C. Their triclinic crystal structures were determined by means of X-ray single crystal data (space group P1̅, a=863.960(10)/903.2(3), b=942.790(10)/982.1(3), c=1182.70(2)/1227.4(4) pm, α=77.4740(10)/77.262(6), β=71.5250(10)/71.462(6), γ=63.7560(10)/63.462(5)°, Z=1, R1=0.0308/0.0658 for Q=S/Se). The structures contain isolated dinuclear anions [FeIII2Q6]6− composed of two edge-sharing [FeQ4] tetrahedra (dFe−Q =223.4–232.3/236.2–244.8 pm), which are also found in the two polymorphs of the pure alkali diferrates Rb6[Fe2Q6]. The diferrate ions are arranged in layers running in the a/b plane around z=0. Inbetween (around $z \approx {1 \over 2}$), two crystallographically different disulfide/diselenide ions $Q_2^{2 - }$ (dQ−Q =211.1–213.4/237.9–241.1 pm), which are arranged in slightly puckered 36 nets, are intercalated. The intra-anionic distances and angles, the Rb coordination numbers and the molar volumes of these two ‘double-salts’ are in accordance with their corresponding reference compounds, Rb6[Fe2Q6] and Rb2Q2. In addition, the two polymorphs of Rb6[Fe2Se6], which are both isotypic with the sulfido analogous (Cs6[Ga2Se6]-type, monoclinic, space group P21/c, a=827.84(5), b=1329.51(7), c=1074.10(6) pm, β=127.130(5)°, R1=0.0443 and Ba6[Al2Sb6]-type, orthorhombic, space group Cmce, a=1963.70(3), b=718.98(3), c=1348.40(7) pm, R1=0.0264) were prepared and characterized to complete the series of alkali diferrates(III) with oxido, sulfido and selenido ligands. The electronic band structures of the three Rb salts Rb6[Fe2Q6], which have been calculated within the GGA+U approach applying an AFM spin ordering in the dimers and appropriate Hubbard parameters, allow a comparison of the chemical bonding characteristics (e.g. covalency) and the magnetic properties (magnetic moments) within the series of chalcogenido ligands. An analysis of the spin densities enables a comparative consideration of the mechanisms crucial for the magnetic ordering in chalcogenido ferrates. Ultimately, the electronic structure of the new compound Rb12[Fe2S6](S2)3 nicely compares with those of the S2-free reference compound Rb6[Fe2S6].

Electronic Structure of Rare-Earth Pnictides for Metallization of Semiconductors

1994 ◽  
Vol 337 ◽  
Author(s):  
A. G. Petukhov ◽  
W. R. L. Lambrecht ◽  
B. Segall
Keyword(s):  
Experimental Data ◽  
Rare Earth ◽  
Magnetic Moments ◽  
Magnetic Exchange ◽  
Cross Sectional ◽  
Electronic Band ◽  
Lattice Constants ◽  
Rocksalt Structure ◽  
Cohesive Energies ◽  
Electronic Band Structures

ABSTRACTThe results of first-principles calculations of the electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli, and magnetic moments are presented for the rare-earth pnictides with the rocksalt structure and chemical formula RX, where R = Gd, Er and X = N, P, As. Some of these materials are semimetals and are suitable for metallization of III-V semiconductors. The results for the lattice constants are in good agreement with experimental data. For ErAs, which is closely lattice-matched to GaAs, the calculated magnetic exchange splittings, electron and hole concentrations, Fermi surface cross-sectional areas and cyclotron masses are found to be in satisfactory agreement with the available experimental data.

New sodium-rich mixed Mn/In chalcogenido metallates Na12MnIn2Q10 (Q = S, Se)

2020 ◽  
Vol 75 (9-10) ◽  
pp. 825-832
Author(s):  
Michael Langenmaier ◽  
Julian Brantl ◽  
Caroline Röhr
Keyword(s):  
Structure Type ◽  
Close Packing ◽  
Monoclinic Space Group ◽  
Crystallographic Site ◽  
Slow Cooling ◽  
Sodium Cations ◽  
Structure Relation ◽  
Pure Phase ◽  
Maximum Temperatures ◽  
Tetrahedral Voids

AbstractThe sodium-rich sulfido and selenido metallates Na12MnIn2Q10 (Q = S/Se) were synthesized in pure phase from melts composed of stoichiometric quantities of the manganese monochalcogenides MnQ, elemental indium and the chalcogens together with either Na2S (Q = S) or elemental sodium (Q = Se) as starting material. The samples were heated up to maximum temperatures of 1000/900 °C under an argon atmosphere; crystallization was achieved by slow cooling rates of 10 K h−1. The two isotypic compounds (monoclinic, space group P21/m, a = 678.26(2)/698.85(10), b = 2202.77(7)/2298.7(3), c = 766.39(3)/800.59(13) pm, β = 90.232(2)/90.147(5)°, Z = 2, R1 = 0.0516/0.0575) crystallize in a new structure type. According to the division of the formula as Na12[InQ4][MnInQ6] the salts contain ortho indate anions [InIIIQ4]5− besides hetero-bimetallic dimers [MnIIInIIIQ6]7−, which consist of two edge-sharing [MQ4] tetrahedra. The seven crystallographically different sodium cations exhibit an either tetrahedral or octahedral coordination by the chalcogen atoms. Thus, the overall structure of the salt is best described by a hexagonal close packing of the sulfide/selenide anions, in which the octahedral voids of every second interlayer section are fully occupied by the (overall 5/f.u.) Na+ positions with CN = 6. In the other half of the interlayer sheets, all tetrahedral voids (overall 10/f.u.) are occupied by the seven CN = 4 Na+ cations, one In3+ of the ortho anion and the two Mn2+/In3+ cations (which statistically occupy one crystallographic site). This structure relation is also verified by a Bärnighausen group-subgroup tree connecting the h.c.p. (Mg type) aristotype (with its tetrahedral and octahedral voids) by an overall index of 60 with the structure of the two title compounds.

Electronic band structures of NdFe3(BO3)4 and NdGa3(BO3)4 crystals: ab initio calculations

2021 ◽  
Vol 575 (1) ◽  
pp. 11-17
Author(s):  
S. Krylova ◽  
I. Gudim ◽  
A. Aleksandrovsky ◽  
A. Vtyurin ◽  
A. Krylov
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Band Structures ◽  
Electronic Band ◽  
Electronic Band Structures

scholarly journals Phase-selective active sites on ordered/disordered titanium dioxide enable exceptional photocatalytic ammonia synthesis

2021 ◽  
Author(s):  
Jinsun Lee ◽  
Xinghui Liu ◽  
Ashwani Kumar ◽  
Yosep Hwang ◽  
Eunji Lee ◽  
...  
Keyword(s):  
Titanium Dioxide ◽  
Active Sites ◽  
Rational Design ◽  
Ammonia Synthesis ◽  
Reduction Reaction ◽  
Band Structures ◽  
Electronic Band ◽  
Defect Sites ◽  
Electronic Band Structures ◽  
Reaction Routes

This work highlights the importance of a rational design for more energetically suitable nitrogen reduction reaction routes and mechanisms by regulating the electronic band structures with phase-selective defect sites.

Molecular Vibrations in the Exciton Theory for Molecular Aggregates. II. Dimeric Systems

1961 ◽  
Vol 14 (3) ◽  
pp. 344 ◽  
Author(s):  
EG McRae
Keyword(s):  
Absorption Spectrum ◽  
Perturbation Theory ◽  
Fluorescence Spectra ◽  
Numerical Calculations ◽  
Molecular Vibrations ◽  
Molecular Aggregates ◽  
Absorption And Fluorescence Spectra ◽  
Band Structures ◽  
Electronic Band ◽  
Electronic Band Structures

The theory of Part I of this series (McRae 1961) is developed in detail for dimeric systems. The simplest possible theory of the exciton states for a system of two non-rigid molecules is obtained through the use of perturbation theory. The theory makes possible the prediction of electronic band structures in absorption and fluorescence spectra as functions of the theoretical Davydov splitting for two rigid molecules. Numerical calculations are made for a dimer of a typical dye, and the results are compared with the observed absorption spectrum of the 1,1'-diethyl-2,2'-pyridocyanine iodide dimer.

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