Parameters of crystal and electronic structure and magnetic properties of mechanically alloyed Ni3C cubic carbide

The cubic Ni3.3C carbide has been fabricated by mechanical alloying of elemental Ni powder and the multiwalled carbon nanotubes in a high energy planetary ball mill. Crystal structure of carbide obtained belongs to the defective structure of ZnS sphalerite type according to x-ray diffraction data. Parameters of the electronic structure of Ni3.3C were calculated by linearized muffin-tin orbitals method within the plane-wave approximation using as an input the defined parameters of crystal structure. Magnetic properties, such as temperature and field dependences of the magnetic susceptibility of Ni3.3C have been studied. Based on experimental data obtained by studying the crystal structure and magnetic properties of Ni3.3C, as well as on the basis of calculations of electronic structure parameters, a preferred displacement of the carbon atoms in tetrahedral voids of Ni crystal lattice has revealed.

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

The 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.

New compounds of the Li2MSn3S8 type

The substitution of Cu/Ag by lithium in complex thiospinels with the general formula AI2BIICIV3XVI8 was achieved by ball milling and a subsequent annealing step in an atmosphere of H2S. Four hitherto unknown compounds Li2MSn3S8 with M = Mg, Mn, Fe, Ni were obtained without side phases and have been structurally investigated. From X-ray powder diffraction experiments, space group Fd$\overline{3}$m and a spinel-type structure are suggested. In these so-called normal spinels, lithium occupies one eighth of the tetrahedral voids (Wyckoff position 8a) of the cubic closest packing of the sulfide ions whereas M and Sn can be found on one half of the octahedral voids (Wyckoff position 16d).

Electronic stabilization by occupational disorder in the ternary bismuthide Li3–x–y In x Bi (x ≃ 0.14, y ≃ 0.29)

A ternary derivative of Li3Bi with the composition Li3–x–y In x Bi (x ≃ 0.14, y ≃ 0.29) was produced by a mixed In+Bi flux approach. The crystal structure adopts the space group Fd\overline{3}m (No. 227), with a = 13.337 (4) Å, and can be viewed as a 2 × 2 × 2 superstructure of the parent Li3Bi phase, resulting from a partial ordering of Li and In in the tetrahedral voids of the Bi fcc packing. In addition to the Li/In substitutional disorder, partial occupation of some Li sites is observed. The Li deficiency develops to reduce the total electron count in the system, counteracting thereby the electron doping introduced by the In substitution. First-principles calculations confirm the electronic rationale of the observed disorder.

Technological scheme of fi nishing and strengthening of parts in screw working elements machines and rationale for their drive power

Typical technological scheme of the machine for finishing and cleaning and strengthening treatment with working elements in the form of screw rotors mounted from tetrahedral voids is presented. Method for calculating of the drive of these machines is proposed, taking into account the load mass, the working element mass and the load mass located asymmetrically in the working element of the rotation axis, which allows you to calculate the power of the electric motors of machines for finishing, cleaning and strengthening treatment taking into account the actions of symmetrical and asymmetric loading processed parts and particles of the working medium relative to the rotation axis of the screw rotor.

Size Matters: New Zintl Phase Hydrides of REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) with Large and Small Cations

Many Zintl phases exhibiting a CrB type structure form hydrides. Systematic studies of AeTtHx (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn), LnTtHx (Ln = La, Nd; Tt = Si, Ge, Sn), and LnGaHx (Ln = Nd, Gd) showed the vast structural diversity of these systems. Hydrogenation reactions on REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) were performed in steel autoclaves under hydrogen pressure up to 5 MPa and temperatures up to 773 K. The products were analyzed by X-ray and neutron powder diffraction. RESi (RE = Y, Er, Tm) form hydrides in the C-LaGeD type. LaGaD1.66 is isostructural to NdGaD1.66 and shows similar electronic features. Ga-D distances (1.987(13) Å and 2.396(9) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. In TmGaD0.93(2) with a distorted CrB type structure deuterium atoms exclusively occupy tetrahedral voids. Theoretical calculations on density functional theory (DFT) level confirm experimental results and suggest metallic properties for the hydrides.

Investigation of structural, thermodynamic and energy state characteristics of the ZrNi1-xRhxSn solid solution

The peculiarities of crystal and electronic structures, thermodynamic and energy state characteristics of the ZrNi1-xRhxSn semiconductive solid solution were investigated. It has been shown that in the ZrNiSn compound simultaneously exist two types of structural defects of the donor nature which generate two donor bands with different ionization energy in the band gap: a) the donor band ɛD1, formed as a result of a partial, up to ~ 1%, occupation of 4a position of Zr atoms by Ni atoms (mechanism of “a priori doping”) and deep donor band ɛD2, formed as a result of partial occupation of the tetrahedral voids by Ni atoms (Vac). The substitution in 4c position of the Ni atoms by Rh ones in ZrNi1-xRhxSn generates structural defects of acceptor nature and creates an impurity acceptor band ɛA in the band gap, which, in addition to the existence of ɛD1 та ɛD2 donor bands, makes semiconductor highly doped and strongly compensated. The obtained results allow to understand the mechanisms of electrical conductivity of thermoelectric materials based on n-ZrNiSn and the ways of conscious optimization of their characteristics for obtaining the maximum efficiency of conversion of thermal energy into electric.

Влияние водорода на флуктуационное охрупчивание алюминия

The main processes occurring during vacancy generation in aluminum in the presence of hydrogen are described on the base of ab initio methods using the meta-functional SCAN. It was shown that hydrogen reduces the vacancy generation energy from 2.8 eV to 0.8 eV. In this case, eight hydrogen atoms located in the tetrahedral voids of the lattice around one aluminum atom make it much easier for it to move to the interstitial site. In accordance with the kinetic concept of embrittlement the dependence of the activation energy of hydrogen embrittlement of aluminum is calculated on the concentration of hydrogen and temperature. It is shown that hydrogen reduces the time of aluminum embrittlement only if its concentration in aluminum is more than critical one (~3⋅〖10〗^(-4) at T=293 K).

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

The 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.

Another step toward the solution of the real structure of zinkenite

The crystal structure of Cu-bearing zinkenite from Saint-Pons (Alpes Maritimes department, France), having idealized chemical composition Cu0.7Pb9.7Sb21.3S42, has been studied. It has a pronounced hexagonal sub-cell, with unit-cell parametersa=22.1219(11),c=4.3207(3) Å,V=1831.2(2) Å3, space groupP63,Z=1. The sub-cell crystal structure was refined toR1=0.072 on the basis of 3905 reflections withFo>4σ(Fo) and 133 refined parameters. It can be described as formed by one kind of rod, with walls of columns of (Pb/Sb)-centered polyhedra flanking both the rods and the sites located along the 63screw axis. Minor Cu is hosted in the tetrahedral voids between the rods and the walls of polyhedra. Alternatively, the crystal structure of zinkenite can be described as formed by trigonal rods, delimited by lone electron-pair micelles, and tunnels hosting (Pb/Sb) atoms. The occurrence of weak superstructure reflections points to a triclinic unit cell with parametersa=38.271(2),b=22.1219(13),c=8.6475(5) Å, α=89.931(3), β=90.030(3), γ=89.957(3)°,V=7323.6(7) Å3, space groupP1,Z=4. The twin laws making the twin lattice hexagonal have been taken into account and the crystal structure has been solved and refined. Notwithstanding the very lowR1value (R1=0.038 on the basis of 22563 reflections withFo>4σ(Fo) and 1194 refined parameters), several shortcomings, mainly due to the low diffraction quality of the available crystals, allow only the description of the main structural features of the superstructure of zinkenite, indicating the correctness of the triclinic model hypothesized by previous authors.