Space Group F4 Research Articles

Investigation on new equiatomic quaternary Heusler compound CoCrIrSi via FP-LAPW calculations

In this work, we have studied the structural, elastic, electronic and magnetic properties of CoCrIrSi EQH compound basing on the first principles calculations. CoCrIrSi is found to be energetically favorable in face-centered cubic (FCC) structure with space group F4‾3m, in which Co, Cr, Ir and Si atoms are located at 4c, 4b, 4d and 4a Wyckoff positions, respectively. Our results show that CoCrIrSi is mechanically stable and ductile. Electronic calculations indicate that CoCrIrSi is half-metallic with relatively large spin-down band gap of 0.741 eV. Otherwise, magnetic properties of CoCrIrSi do obey Slater-Pauling rule. The effect of uniform strain and tetragonal deformation on the half-metallicity is also studied. Finally, the thermodynamic properties of CoCrIrSi are calculated under large range of temperature up to 1200 K and pressure up to 30 GPa, using Debye quasi-harmonic model, and the obtained results will be discussed in detail.

Synthesis, structure and properties of a calcium oxonitridosilicate phosphor showing green or red luminescence upon doping with Eu2+ or Ce3.

The phase LixCa16-xSi17N32-xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F4[combining macron]3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16-xSi17N32-xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350-480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.

Crystal growth, structural and electrical properties of (Cu1-хAgx)7GeS5I superionic solid solutions

Single crystals of (Cu1-хAgx)7GeS5I solid solutions were grown by vertical zone crystallization method. XRD studies have shown that they crystallize in face-centered cubic lattice of the argyrodite structure (space group F4¯3m, Z = 4). Structural studies were performed on the basis of original structure model by means of Rietveld refinement method. Electrical measurements were carried out in the temperature interval 300–360 K and in the range of frequencies 10 Hz–10 GHz. Temperature and frequency dependences of electrical conductivity were analyzed. Influence of cation substitution on the electrical conductivity as well as relationship between structural and electrical properties of (Cu1-хAgx)7GeS5I solid solutions were studied.

Determination of atomic positions and polar direction in half-Heusler material Sb1-xSnxTi1-y-zHfyZrzCo using electron channeling

Variation of electron-induced x-ray emission with the crystal direction of an incoming electron beam (channeling) is used to study the crystal site preference of different elements in a promising thermoelectric half-Heusler material. This material has Sb, Co and Ti as the main constituting elements, with lower contents of Hf, Zr and Sn. It is confirmed experimentally, in accordance with previous assumptions, that Sb and Sn occupy one of the octahedral sites, 4a (0, 0, 0), Ti, Zr and Hf the other octahedral site, 4b (½, ½, ½), and Co atoms occupy the tetrahedral site, 4c (¼, ¼, ¼) in the cubic spacegroup F4¯3m with lattice constant a = 0.598 ± 0.001 nm. Furthermore, a strong asymmetry along the polar directions is observed, which is as it should be in a half-Heusler material, when the Co atoms have a strong preference for one of the two sets of tetrahedral sites. Such asymmetries can not be observed by kinematical diffraction according to Friedel’s law, thus demonstrating that the observation of element characteristic signals under channeling conditions is a unique technique for determining the sense of polar directions and distinguishing crystal symmetry alternatives in small crystal grains and nanocrystals.

Crystal structure and magnetic properties of the selected phases from the R-{Co, Ni}-Al (R = Y, Gd-Tm) systems

Ternary aluminides, R10(Co,Ni)Al3, R14(Co,Ni)3Al3, R6(Co,Ni)2Al, R3Co3Al and R4CoAl (R = Y, Gd-Tm), have been prepared by arc-melting of the metals and annealed at 600 °C. Their crystal structure has been investigated by means of powder X-ray diffraction analysis. The phases belong to the known structure types, namely, Y10RuCd3 (space group P63/mmc, Pearson symbol hP28, Z = 2), Gd14Co3In3 (space group P42/nmc, Pearson symbol tP80, Z = 4), Ho6Co2Ga (space group Immm, Pearson symbol oI36, Z = 4), Y3Co3Ga (space group Cmcm, Pearson symbol oC28, Z = 4) and Gd4RhIn (space group F4¯3m, Pearson symbol cF96, Z = 16). Structural peculiarities, coordination and interactions of the atoms in the Ho6Co2Al, Ho10CoAl3 and Tm14Ni3Al3 compounds have been briefly discussed. Bulk magnetic studies were performed for representative Ho10CoAl3, Er10CoAl3 and Tm10CoAl3 compounds and it was found that they order antiferromagnetically at temperatures TN equal to 23.8 K, 14.8 K, and 7.4 K, respectively.

Structure and physical properties of quaternary Heusler alloy NiMnCuSb

The relationship between structure and physical properties such as magnetic moment and Curie temperature is studied theoretically for the recently synthesized equiatomic quaternary Heusler alloy CuNiMnSb, which is found to crystallize in the LiMgPdSb structure. Calculations are performed for various different possible structural phases within the framework of the D03-type structure (space group F4¯3m) by changing the sequence of the atoms along the body diagonal of fcc lattice that characterizes the structure of this alloy. Total energy, magnetic moment and the Curie temperature results, in particular the latter two, suggest that the correct order of the atoms along the body diagonal is most likely Ni(0,0,0), Mn(0.25,0.25,0.25), Cu(0.5,0.5,0.5) and Sb(0.75,0.75,0.75) in contrast to (disagreement with) the conclusions of a recent experimental study. Neither the sequence Ni-Cu-Mn-Sb nor Ni-Mn-Cu-Sb shows a large spin polarization at the Fermi level.

A new superlattice structure in the Al2.75Ir and Al2.63Rh 1/0 approximants

We investigate the superstructure of binary Al2.75Ir and Al2.63Rh 1/0 approximants by X-ray diffraction method and transmission electron microscopy. Al2.75Ir possesses a 2a × 2a × 2a C-centred monoclinic lattice with space group C2 or Cm or C2/m. Al2.63Rh possesses a 2a × 2a × 2a face centred lattice with space group F23 or Fm3.

Density-functional study of plutonium monoxide monohydride

The structural, electronic, mechanical, optical, thermodynamic properties of plutonium monoxide monohydride (PuOH) are studied by density-functional calculations within the framework of LDA/GGA and LDA/GGA+U. From the total energy calculation, the lowest-energy crystal structure of PuOH is predicted to have space group F4¯3m (No. 216). Within the LDA+U framework, the calculated lattice parameter of F4¯3m-PuOH is in good agreement with the experimental value and the corresponding ground state is predicted to be an antiferromagnetic charge-transfer insulator. Furthermore, we investigate the bonding character of PuOH by analyzing the electron structure and find that there are a stronger Pu-O bond and a weaker Pu-H bond. The mechanical properties including the elastic constants, elastic moduli and Debye's temperature, and the optical properties including the reflectivity and absorption coefficient are also calculated. We then compute the phonon spectrum which verified the dynamical stability of F4¯3m-PuOH. Some thermodynamic quantities such as the specific heat are evaluated. Finally we calculate the formation energy of PuOH, and the reaction energies for the oxidation of PuOH and PuOH-coated Pu, which are in reasonable agreement with the experimental values.

Synthesis and characterization of [formula omitted] and [formula omitted] (RE = Nd, Sm) as hettotypes of the [formula omitted] structure type

The mercury-rich amalgams La11+xHg45−x and RE11Hg44.5 (space group F4¯3m (No. 216), La11+xHg45−x: a = 21.9342(19)Å, RE = Nd: a = 21.7384(14)Å; RE = Sm: a = 21.6555(4)Å), were synthesized by dissolving the respective rare earth metals in a mercury surplus and subsequently distilling off the excess. The compounds were characterized by single crystal and powder X-ray methods together with ab-initio band structure calculations. Both crystal structures deviate significantly and in different ways from their common aristotype, the Sm11Cd45 structure type. In La11+xHg45−x (x = 0.7(1)) two crystallographic sites show mixed occupancy, whereas in RE11Hg44.5 one of the Hg positions is fully unoccupied. Their band structures exhibit typical broad Hg d states at low energies, and a strong mixing of s and p states indicates a mercury sublattice with high connectivity.

The low and high temperature thermoelectric properties of Sb doped Cu2SnSe3

The effect of Sb doping on the thermoelectric properties of Cu2SnSe3 was investigated. The Cu2Sn1⿿xSbxSe3 (0⿤x⿤0.04) compounds were prepared by solid state synthesis. The powder X-ray diffraction pattern of the samples showed a cubic structure (space group F4¯3m). The electrical resistivity decreased with increase in Sb content up to x=0.02, then it increased with further increase in x. The electrical resistivity data follows variable hopping model at low temperatures. The Seebeck coefficient for all the samples is positive and analysis of data confirms that the variable hopping process is operative at low temperatures. The thermal conductivity is found to decrease with increase in Sb concentration, presumably due to point-defect scattering as a result of Sb substitution. The highest value of figure of merit at 400K is equal to 0.0137 for the sample Cu2Sn0.99Sb0.01Se3 which is about eight times greater than that of the pristine sample.

Electrical and thermal transport properties of [formula omitted] compounds, RE=Nd, Gd

We report the electrical and thermal transport properties of NdCu4Au and GdCu4Au compounds, crystallizing in the cubic MgCu4Sn - type crystal structure, with space group F4¯3m (no. 216).These properties are reported through measurements of electrical resistivity, ρ(T), thermoelectric power, S(T) and thermal conductivity, λ(T). ρ(T) and S(T) data indicate an antiferromagnetic (AFM)-like anomaly associated with a Néel temperature TN=3.9K and 10.9K for NdCu4Au and GdCu4Au compounds, respectively. ρ(T) data for both compounds shows a sudden drop at TN. Above TN, ρ(T) results are characteristic of an electron–phonon interaction in the presence of s−d scattering. Application of magnetic field slightly suppresses TN value in GdCu4Au compound from TN=10.9K in a field of 0T to 10.1K in a field of 6T. S(T) data at low temperatures for both compounds shows a minimum at TN. Critical analysis of S(T) in terms of the phenomenological resonance model yield the positions (Ef) and bandwidths (Wf) of the 4f - band in both compounds: Ef=3.81(6)K, Wf=329(58)K for the Nd compound and Ef=18.2(4)K, Wf=306(5)K for the Gd compound. λ(T) for both compounds decreases linearly upon cooling from room temperature. The reduced Lorentz number L/L0 deviates from the Wiedmann–Franz at low temperature with a strong increase in L/L0 upon cooling the samples from room temperature.

Crystal structure and thermodynamic properties of NdCu4Au compound

We report the synthesis of the antiferromagnet cubic-type structure NdCu4Au derived by substituting Au for Cu in the parent binary NdCu5 compound. The room temperature X-ray diffraction analysis indicates a cubic MgCu4Sn-type structure with space group F4¯3m (No. 216) for the NdCu4Au compound. The thermodynamic properties of NdCu4Au have been probed by magnetic susceptibility, χ(T), magnetization, M(μ0H), and specific heat, Cp(T), measured down to 1.8K. The low temperature χ(T) data shows probably an antiferromagnetic (AFM)-like anomaly associated with a Néel temperature TN=3.9K. In the paramagnetic region, χ(T) data follows the modified Curie–Weiss law with an effective magnetic moment μeff=3.547(5)μB and Weiss temperature θp=−10.19(8)K. The value for μeff is close to the value of 3.62μB expected for the Nd3+-ion. No evidence of metamagnetic transition was observed from the isothermal M(μ0H) results. Cp(T) data confirm the AFM phase transition at TN=3.5K close to the value of 3.9K observed in χ(T). The 4f-electron specific heat shows a Schottky-type anomaly around 20K associated with crystalline-electric-field (CEF), with energy splitting Δ1=62(5)K and Δ2=109(9)K of the Nd3+ (J=9/2) multiplet, that are associated with the first and second excited state of Nd3+-ion. From the results of the 4f-electron magnetic entropy, it is speculated that the CEF ground state of Nd3+ (J=9/2) ions is the Γ6 doublet for NdCu4Au.

Tululite, Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36: a new Ca zincate-aluminate from combustion metamorphic marbles, central Jordan

Tululite (Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36 (the hypothetical end-member formula Ca14{Fe3+O6}[SiO4][Zn5Al9]O26) (IMA2014-065) is a new natural Ca zincate-aluminate, identified in medium-temperature (800–850 °C) combustion metamorphic (CM) spurrite-fluorellestadite marbles from central Jordan. The type locality (Tulul Al Hammam area) is situated in the northern part of the Siwaqa complex, the largest area of the “Mottled Zone” Formation in the Dead Sea region. The marbles originated from bitumen-rich chalky marine sediments of the Maastrichtian-Paleogene Muwaqqar Chalk Marl Formation, which have low clay content (and, consequently, low Al) and high Zn, Cd, and U enrichments. The bulk CM rocks derived from the low-Al protolith have unusually high (Zn + Cd)/Al ratios (~0.2) and, as a result, a mineralogy with negligibly small percentages of Ca aluminates having low Ca:Al molar ratios (minerals of mayenite supergroup, Ca:Al = 6:7) common to most of calcareous CM rocks in the Mottled Zone. Instead, the mineral assemblage of the Zn-rich marbles contains tululite, with high Ca:Al = 2.55 molar ratios and Zn substituting for a large portion of Al (Zn:Al = 1.1). Tululite occurs in thin clusters as irregular grains with indented outlines (20–100 μm in size), having typical open-work textures associated with rock-forming calcite, fluorellestadite, spurrite, and accessory Zn-rich periclase, lime-monteponite solid solutions, calcium uranates, and zincite. Marbles also bear brownmillerite, dorrite, fluormayenite, high-fluorine Ca aluminate, and lakargiite. Secondary phases are brucite, gel-like calcium silicate hydrates and calcium silicate aluminate hydrates, including Zn- and U-bearing and Cd-rich compounds, Si-bearing hydrated compounds after calcium uranates, and basic Cd chlorides. The empirical formula of the holotype tululite (a mean of 32 analyses) is (Ca13.29Cd0.75)Σ14.04(Al5.46Zn5.20Fe3+ 2.23Si0.95Mn3+ 1.01Mg0.78P0.41)Σ16.04O36. Tululite is cubic, space group F23; a = 14.9346(4) A; V = 3331.07(15) A3, Z = 4. The strongest lines of the X-ray powder-diffraction pattern [d, A – (I obs )] are: 2.874(57), 2.640 (100), 2.524(42), 2.278(41), 1.760(54), 1.725(25), 1.524(33), 1.500(33). The crystal structure was solved from single-crystal X-ray diffraction data and refined to wR2 = 0.0672 on the basis of 913 unique reflections with I 0 > 2σ(I). Tululite belongs to a group of compounds with the general formula Ca14 MT 15O35+x (0 ≤ x ≤ 1), and is a new structure type. The tetrahedral framework of tululite structure is formed by T7O13 secondary building units (SBU), which consist of four corner-linked tetrahedra sharing a common oxygen atom and three tetrahedra sharing two O atoms with the neighbor SBU. Ca2+ cations occupy three positions; two of them also contain a minor amount of Cd2+. The Ca sites surround an island (Fe3+,Al)O6 octahedron and a (Si,P)O4 tetrahedron in the centers of framework cages at the junction of eight SBUs. The (Fe3+,Al)O6 octahedron is coordinated by fourteen Ca positions into a 6-capped cube, whereas the (Si,P)O4 tetrahedron is coordinated by six Ca positions into a regular octahedron. The structural formula of tululite is Ca14{Fe3+O6}M1[(Si,P)O4]T1[(Al,Zn)7O13]2 T2-T4. The mineral is yellow with greenish tint, transparent with vitreous luster, non-fluorescent under ultraviolet light, and showing neither parting nor cleavage; Mohs hardness is 6.5. The density calculated on the basis of the empirical formula is 3.826 g/cm3. Its Raman spectrum shows strong bands at 522, 550 and 636 cm−1 and weak bands at 199, 260, 295, 456, and 754 cm−1.

Mössbauer spectroscopy, magnetic, and ab initio study of the Heusler compound Fe2NiGa

The structural, electronic, magnetic, elastic, and hyperfine-interaction properties of Fe2NiGa have been determined by means of X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetic measurements and ab initio calculations. The compound studied crystallizes in the cubic space group F4¯3m with lattice constant a=5.7961(4)A˚. Evidence is provided for the presence of significant structural disorder in the compound. Fe2NiGa is predicted to be half-metallic with covalent chemical bonding. It orders ferromagnetically with the Curie temperature TC=586.0(7)K. The saturation magnetization per formula unit and the estimated Fe magnetic moments at the A and B sites are 3.00, 1.87(2), and 2.25(2) μB, respectively. The ab initio calculations overestimate the values of the A- and B-site Fe magnetic moments. It is observed that the magnetic properties of Fe2NiGa are very strongly dependent on its heat treatment. The calculated hyperfine-interaction parameters show general agreement with the experimental ones. It is demonstrated that the compound studied decomposes when heated and kept at temperatures above around 500K. The Debye temperature of Fe2NiGa is found to be 378(5)K.

Structure of type II dehydroquinase from Pseudomonas aeruginosa.

Pseudomonas aeruginosa causes opportunistic infections and is resistant to most antibiotics. Ongoing efforts to generate much-needed new antibiotics include targeting enzymes that are vital for P. aeruginosa but are absent in mammals. One such enzyme, type II dehydroquinase (DHQase), catalyzes the interconversion of 3-dehydroquinate and 3-dehydroshikimate, a necessary step in the shikimate pathway. This step is vital for the proper synthesis of phenylalanine, tryptophan, tyrosine and other aromatic metabolites. The recombinant expression, purification and crystal structure of catalytically active DHQase from P. aeruginosa (PaDHQase) are presented. Cubic crystals belonging to space group F23, with unit-cell parameters a=b=c=125.39 Å, were obtained by vapor diffusion in sitting drops and the structure was refined to an R factor of 16% at 1.74 Å resolution. PaDHQase is a prototypical type II DHQase with the classical flavodoxin-like α/β topology.

CrZn17+δ (−0.75 ⩽ δ ⩽ 2.00): A partly disordered complex intermetallic compound

The γ-brass related phase CrZn17+δ(−0.75⩽δ⩽2.00) in the Cr–Zn binary system has been synthesized and the structure has been analyzed by powder and single crystal X-ray diffraction. The compound crystallizes in the cubic space group F4¯3m (216). The unit cell contains 400–403 atoms. The phase width arises due to a disorder phenomenon. The structure can be described as an arrangement of nested polyhedral units, centered at sites of high symmetry points. The phase melts incongruently at ∼744K. Electronic structure calculations, using the tight-binding linear muffin-tin orbital atomic spheres approximation (TB-LMTOASA) method on the model of ordered “Cr5Zn96” shows the presence of a pseudogap at the Fermi level in the electronic density of states curves.

Expression, purification, crystallization and preliminary X-ray analysis of full-length human RIG-I

The human innate immune system can detect invasion by microbial pathogens through pattern-recognition receptors that recognize structurally conserved pathogen-associated molecular patterns. Retinoic acid-inducible gene I (RIG-I)-like helicases (RLHs) are one of the two major families of pattern-recognition receptors that can detect viral RNA. RIG-I, belonging to the RLH family, is capable of recognizing intracellular viral RNA from RNA viruses, including influenza virus and Ebola virus. Here, full-length human RIG-I (hRIG-I) was cloned in Escherichia coli and expressed in a recombinant form with a His-SUMO tag. The protein was purified and crystallized at 291 K using the hanging-drop vapour-diffusion method. X-ray diffraction data were collected to 2.85 Å resolution; the crystal belonged to space group F23, with unit-cell parameters a = b = c = 216.43 Å, α = β = γ = 90°.

La10W2O21: An Anion-Deficient Fluorite-Related Superstructure with Oxide Ion Conduction

The crystal structure of La10W2O21, which has to be reformulated (La5.667W0.333)LaWO14□2, is best described, on average, by a 2 × 2 × 2 anion-deficient fluorite-related superstructure cubic cell, with space group F4 3m, Z = 4, and a = 11.17932(6) Å, similar to Y7ReO14--δ. The 32 cations are distributed with lanthanum on the 4a-site, tungsten on the 4b-site, and a partial occupancy of the 24g-site by La (94%) and W. The 56 oxygen atoms occupy four 16e-sites, three of them fully and with an occupancy of 1/2 for the fourth one. Others M10W2O21 (M = Er, Y) adopt a 3 × 2 × 2 fluorite superstructure with W in octahedral sites, whereas W is mainly in tetrahedral sites in La10W2O21. Several powerful techniques such as crystal image furnace synthesis, (139)La nuclear magnetic resonance (NMR) and convergent beam electron diffraction (CBED) were used to achieve our results. Transmission electron microscopy (microdiffraction, CBED, and Tanaka patterns) brought us the real symmetry, showing that indeed classical cubic twinning along the 3-fold axis does take place. The surprising La/W mixed site is nicely confirmed by (139)La NMR. This compound exhibits interesting fast oxide ion conducting properties, comparable with LAMOX (Lacorre et al. Nature 2000, 404, 856-858) at low temperature. As opposed to many ionic conductors, no temperature structural transition is observed. Its conductivity is about 6.4 × 10(-4) S·cm(-1) at 700 °C.

Expression, purification, crystallization and preliminary crystallographic analysis of hepatitis B virus core protein dimerized via a peptide linker containing an EGFP insertion.

Virus-like particles (VLPs) have many potentially useful applications. The core proteins of human hepatitis B virus self-assemble into icosahedral VLPs. As previously reported, core protein dimers (CPDs), produced by connecting two core proteins via a peptide linker, can also assemble into VLPs. CPDs in which heterologous proteins were connected to the C-terminus (CPD1) were found to rearrange into symmetrical octahedra during crystallization. In this study, a heterologous protein was inserted into the peptide linker of the CPD (CPD2). CPD2 was expressed in Escherichia coli, assembled into VLPs, purified and crystallized. A single crystal diffracted to 2.8 Å resolution and belonged to the cubic space group F432, with unit-cell parameters a = b = c = 218.6 Å. Single-crystal analysis showed that CPD1 and CPD2 rearranged into the same octahedral organization in a crystallization solution.

Growth and structural investigation of new polycrystalline Ga3Se4 semiconductor: Evaluation of its dielectric properties

To establish the powder X-ray data we have synthesized gallium selenide (Ga3Se4) using spec. pure elements gallium and selenium of purity >99.999% adopting three different methods as solid melts, quenching, and quenching⿿annealing. An optimized condition for the synthesis of these materials using evacuated and sealed ampoule has been established. The powder X-ray diffraction analysis revealed that Ga3Se4 can only grow at elevated temperature by quenching and long annealing at suitable temperature. The material prepared by quenching⿿annealing at 500°C over 500h was identified as single phased polycrystalline Ga3Se4, and crystallizes in the cubic cell with ao=5.4531⿫, V=162.155⿫3, Dx=5.375g/cm3, Z=1, parameter of atoms ZGa=3, ZSe=4 and space group F4¯3m. The low values of dielectric constant and dielectric loss confirm that the specimen has very low density of defects. Negative dielectric constant has been found.