- Noncollinear magnetic structure of MnTe2
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The crystallographic and magnetic properties of the MnTe2 compound have been investigated by 125Te Moessbauer spectroscopy and by neutron diffraction on both powder and single-crystal samples. From TN down to 4.2 K, the si
- Burlet,Ressouche,Malaman,Welter,Sanchez,Vulliet
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- FAR-INFRARED REFLECTION SPECTRA, TO- AND LO-PHONON FREQUENCIES, COUPLED AND DECOUPLED PLASMON-PHONON MODES, DIELECTRIC CONSTANTS, AND EFFECTIVE DYNAMICAL CHARGES OF MANGANESE, IRON, AND PLATINUM GROUP PYRITE TYPE COMPOUNDS.
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A study is made of the far-infrared reflection spectra, the phonon frequencies, and the optical and dielectric constants of the pyrites RuS//2, RuSe//2, RuTe//2, OsS//2, OsSe//2, OsTe//2, PtP//2, PtAs//2, and PtSb//2.
- Lutz,Schneider,Kliche
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- The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2AMnTe3 (A=K, Rb), and NaCsMnTe2
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A series of new sodium and mixed Na/A (A = K, Rb, Cs) tellurido manganates have been synthesized from melts of the pure elements (or MnTe) at maximum temperatures of 600-1000°C. The monoclinic crystal structures of the two pure sodium salts Na2Mn2Te3 (space group C2/c, a = 1653.68(2), b = 1482.57(2), c = 773.620(10) pm, β = 117.52°, Z = 8, R1 = 0.0225) and Na2Mn3Te4 (space group C2/m, a = 1701.99(3), b = 438.741(8), c = 691.226(12) pm, β = 90.3171(8)°, Z = 2, R1 = 0.0270) are both based on a hexagonal close packed Te2- arrangement. Na2Mn2Te3 is isotypic with Na2Mn2S3 and Na2Mn2Se3 and contains layers of [MnTe4] tetrahedra, which are connected via common edges to form tetramers [Mn4Te6]. These tetramers are further connected via μ3-Te atoms. Na2Mn3Te4 crystallizes in a new structure type, recently also reported for the selenido salt Na2Mn3Se4. Mn(2) forms ribbons of vertex-sharing dinuclear units ∞1[Te2/2MnTe2MnTe2/2] USD_infty ^1[{rm{T}}{{rm{e}}_{2/2}}{rm{MnT}}{{rm{e}}_2}{rm{MnT}}{{rm{e}}_{2/2}}]USD running along the short b axis of the monoclinic cell. The Te atoms of these ribbons are also the ligands of edge-sharing [Mn(1)Te6] chains of octahedra. Similar to Na2Mn2Te3, the Na+ cations are octahedrally coordinated and the cations occupy tetrahedral (Mn2+) and octahedral (Na+, Mn2+) voids in the close Te2- packing. The isotypic K/Rb salts Na2AMnTe3 crystallize in a new structure type (orthorhombic, space group Pmc21, a = 1069.70(4)/1064.34(2), b = 1350.24(5)/1350.47(3), c = 1238.82(4)/1236.94(3) pm, Z = 4, R1 = 0.0445/0.0210). In contrast to the simple formula indicating a Mn(III) compound, the complex structure contains one layer consisting of undulated chains of edge-sharing tetrahedra ∞1[MnIITe4/2] USD_infty ^1[{rm{M}}{{rm{n}}^{{rm{II}}}}{rm{T}}{{rm{e}}_{4/2}}]USD separated by free ditelluride dumbbells [Te2]2- and a second layer containing a complex chain of edge- A nd vertex-sharing [MnIITe4] tetrahedra, in which Mn(II) is coordinated to μ1- A nd μ2-Te2- ligands and an η1-ditellurido ligand. The cesium salt NaCsMnTe2 (orthorhombic, space group Cccm, a = 694.21(2), b = 1536.57(4), c = 664.47(2) pm, Z = 4, R1 = 0.0131) likewise forms a new structure type, which is an ordered superstructure of ThCr2Si2. Linear chains ∞1[MnTe4/2] USD_infty ^1[{rm{MnT}}{{rm{e}}_{4/2}}]USD of edge-sharing tetrahedra are connected with similar chains ∞1[NaTe4/2] USD_infty ^1[{rm{NaT}}{{rm{e}}_{4/2}}]USD to form [NaMnTe2] layers. The larger alkali cations Cs+ between the layers exhibit a cubic (CN = 8) coordination.
- Langenmaier, Michael,R?hr, Caroline
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- THERMAL EXPANSION OF MnTe2.
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The thermal expansion of MnTe//2 has been measured. A small anomaly in thermal expansion has been observed at 60 K, which is probably due to a change of internal parameter of crystal. The coefficient of thermal expansion has been separated into lattice, magnetic and Schottky contributions. Results are discussed.
- Kasai,Waki,Ogawa
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- Syntheses, molecular structures, and thermal decomposition of cyclopentadienyldicarbonylmanganese chalcogenide derivatives
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Transmetallation of the dichalcogenide complexes [CpMn(CO) 2]2(μ-X2) (X = S or Se) with M(CO) 5(thf) (M = Cr or W) afforded new heterometallic complexes CpMn(CO)2(μ-Se2)Cr(CO)5,
- Pasynskii,Grigoriev,Torubaev,Blokhin,Shapovalov,Dobrokhotova,Novotortsev
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- MnGa2Te4-II, a high pressure modification of digallium managnese tetratelluride
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MnGa2Te4 has a very complicated crystal structure, in spite of its relatively simple stoichiometric AB2X4 composition. A preliminary crystal structure determination shows that the anions form a distorted cubic close-packed arrangement with all cations located in tetrahedral holes, as in the homologous compound MnIn2Te4. In contrast to MnIn2Te4, however, the occupied Te4 tetrahedra are not only corner-shared, but edge-shared as well. Because the stability of manganese in tetrahedral coordination by tellurium decreases with increasing pressure, a pressure-induced phase transformation for MnGa2Te4 was expected. This paper describes the results of high-pressure experiments with MnGa2Te4 and the structure refinement of the high-pressure phase MnGa2Te4-II.
- Range,Panzer,Klement
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- Synthesis and structures of new layered ternary manganese tellurides: AMnTe2 (A = K, Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2
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The synthesis and crystal structures of new ternary manganese tellurides, AMnTe2 (A = K, Rb, Cs), Na3Mn4Te6, and NaMn1.56Te2, are reported. These compounds are synthesized by solid-state reaction and cation exchange techniques in sealed Nb tubes. The single-crystal structures of AMnTe2 (A = K, Rb), Na3Mn4Te6, and NaMn1.56Te2 have been determined; KMnTe2: a = 4.5110(4) ?, c = 14.909(2) ?, I4m2 (No. 119, Z = 2); RbMnTe2: a = 4.539(1) ?, c = 15.055(2) ?, I4?m2 (No. 119, Z = 2); Na3Mn4Te6: a = 8.274(4) ?, b = 14.083(6) ?, c = 7.608(6) ? β = 91.97(4)°, C2/m (No. 12, Z = 2); NaMn1.56Te2: a = 4.4973(8) ?, c = 7.638(2) ?, P3?m1 (No. 164, Z = 1). The fundamental building blocks of the title compounds are MnTe4 tetrahedra. AMnTe2 (A = K, Rb, Cs) are isostructural with TlFeS2, consisting of layers built up by four corner-shared MnTe4 tetrahedra. Manganese telluride layers in Na3Mn4Te6 consist of two hexagonal nets of Te atoms between which two-thirds of the tetrahedral interstices are filled with Mn atoms to form two 63 honeycomb nets. NaMn1.56Te2 adopts a defective CaAl2Si2 structure type, in which Mn atoms partially and randomly occupy 78% of tetrahedral sites. Temperature-dependent magnetic susceptibilities measurements show that AMnTe2 (A = K, Rb, Cs) exhibit Curie-Weiss paramagnetism, whereas Na3Mn4Te6 and NaMn1.56Te2 show paramagnetism with a weak dependence on temperature.
- Kim, Joonyeong,Wang, Chwanchin,Hughbanks, Timothy
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- Moessbauer and X-ray study of MnTe2
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Experiments on the Moessbauer effect of 125Te and the X-ray diffraction for antiferromagnetic MnTe2 were performed. Temperature dependence of the spin direction has been observed for a magnetic ordering of the first kind fcc lattice. The angle between the spin direction of Mn and the principal axis of electric field gradient increases from 23° at 4.2 K to 30° at 60 K and decreases to 0° at 70 K. Discontinuous changes are found in hyperfine field and quadrupole splitting at 60 K. An analysis of X-ray diffraction intensities for (742), (732) and (721) reflections shows that u parameter increases by 0.0015 at 60 K as temperature decreases and that Einstein temperature increases from 95 K to 105 K below 60 K. The crystallographic phase diagram of MnTe-Te system is given.
- Kasai, Naoko,Nishihara, Yoshikazu,Ogawa, Shinji
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- Magnetic and electrical properties of manganese telluride
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The temperature dependence of the susceptibility of the antiferromagnetic compound MnTe was measured over a range of temperature between liquid nitrogen temperature and 720°C. An abrupt change in slope and a maximum of the susceptibility curve were found at 37°C and at 55°C respectively. These results are compared with the observed Neel temperatures previously reported by Squire and by Serre. A thermal hysteresis was also found above the Neel temperature, relating to the heat history of the specimen. It is shown that the susceptibility of MnTe1+x (O≤x≤1), where x is the excess content of tellurium, is explicable in terms of two phases, MnTe and MnTe2 which possess different susceptibilities. The electrical properties, i.e., the resistivity, the thermo-emf and the Hall emf, were measured as functions of temperature. Evidence was found of anomalous behaviours at the Neel temperature for them. A large thermal hysteresis of the resistivity is also found above the Neel temperature, which suggests a change of the crystal structure at about 130°C.
- Uchida, Enji,Kondoh, Hisamoto,Fukuoka, Nobuo
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- New criteria for the applicability of combustion synthesis: The investigation of thermodynamic and kinetic processes for binary Chemical Reactions
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Combustion synthesis is a novel technique that utilizes the exothermic heat of a chemical reaction to maintain the reaction and to rapidly prepare materials. But, hitherto, none of unified criterion for the validation of combustion synthesis has been proposed. Herein, we proposed the conditions need to be met. In terms of kinetics, at the adiabatic temperature (Tad), the diffusion distance of atoms (lTad) within 0.1 s should be larger than the particle size of the reactants(d), that is, lTad≥d. For systems that satisfy Tad/Tm,L≥1(where Tm,L is the melting point of the low-melting point component of the reactants), the presence of a liquid phase significantly increases the atomic diffusion distance from nanometers to tens of microns, making the criterion lTad≥d simplified to Tad/Tm,L≥1 in most situations. In terms of thermodynamics, the system needs to ensure that the reaction components are in an activated state, that is, Tad/Tm,H ≥0.7, where Tm,H is the melting point of the high-melting point component. The criteria for the SHS reactions proposed in this study further improve the theoretical understanding of SHS reactions, and provide guidance for exploring the ultra-fast synthesis of binary and multicomponent compounds.
- Tan, Xiaoming,Su, Xianli,Yan, Yonggao,Uher, Ctirad,Zhang, Qingjie,Tang, Xinfeng
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supporting information
(2021/01/07)
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- Synthesis and crystal structure of manganese-tris(1,2-ethanediamine)tetratelluride [Mn(en)3]Te4 exhibiting intermolecular interactions between the tetratelluride anions
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Air-sensitive black crystals of the new compound [Mn(en)3]Te4 were synthesized by reacting MnCl2 · 4 H2O, K2Te3 and elemental Te in 1,2-ethanediamine (en) under solvothermal conditions at 433 K. The compound crystallizes in the monoclinic space group P21/n with lattice parameters a = 839.51(7) pm, b = 1551.3(1) pm, c = 1432.6(1) pm, and β = 90.28(2)°. Isolated [Mn(en)3]2+ cations and Te42- anions are arranged in an alternating fashion parallel to the crystallographic b-axis. One terminal Te atom of the Te42- anions exhibits a short intermolecular contact to a neighboured anion thus forming Teg4- anions. A slightly longer interionic Te ... Te separation is observed between two of the inner Te atoms of neighboured Te84- anions. Taking these longer separations into account infinite Te-chains are formed running parallel to [001]. The intermolecular Te ... Te interactions affect the Te-Te bond lengths within the Te42- anion leading to a lengthening of the average Te-Te distance. Short N-H ... Te distances indicate hydrogen bonding between the cations and anions. DTA-TG measurements show that at 441 K the material decomposes in one step. The resulting crystalline material consists of MnTe2 and Te.
- Wendland, Frank,Naether, Christian,Bensch, Wolfgang
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p. 456 - 461
(2008/10/08)
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- Structure of Mercury Telluride-base Solid Solutions in the Hg-Mn-Te System
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The homogeneity field of mercury telluride-base solid solutions is outlined by using quantitative X-ray diffraction analysis (Rietveld and additives methods). The compositions of the solid solutions decline from the HgTe-MnTe section, proving the instability of this section. A structure model of the solid solution at 35 at. % Mn is suggested to explain the instability of the section.
- Bykov,Shevel'kov,Shpanchenko
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p. 440 - 442
(2008/10/08)
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- Synthesis of phosphinochalcogenoic amidato complexes of divalent transition metals and their thermolysis to metal selenide and telluride phases
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Protolysis of the transition-metal diamides [M{N(SiMe3)2}2(thf)n] (M = Cr, Mn, Fe or Co) with 2 equivalents of phosphinochalcogenoic amides But2P(E)NHR (E = Se or Te, R = Pri or cyclo-C6H11) gave a series of thermally stable metal-selenium and -tellurium complexes [M{But2P(E)NR}2]. The complex [Ni{But2P(Se)NR}2] was obtained from Li[But2(Se)NR] and [NiCl2(PMe3)2]. The compounds sublime readily under reduced pressure and are suitable for the gas-phase deposition of metal chalcogenide films. The selenium precursors lead to MSe (M = Cr, Mn, Fe or Ni), while tellurium complexes afford MTe2 (M = Fe, Mn or Co). By contrast, [Co{But2P(Se)NR}2] gives Co3Se4, while [Ni{But2P(Se)NR}2] generates NiSe or Ni6Se5, depending on the deposition conditions.
- Song, Xuejing,Bochmann, Manfred
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p. 2689 - 2692
(2007/10/03)
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