Search

The crystal structure of [NiEn]CrO (En is ethylendiamine), CHCrNNiO is studied: a = 9.0408(5) Å, c = 9.7466(4) Å, V = 689.92(8) Å, space group P6/ mmc, Z = 2, d = 1.704 g/cm, Ni-N 2.133(9) Å, ∠N-Ni-N 82.4(5)°. The thermal properties are determined. When it is heated in a hydrogen atmosphere, a mixture of nanocrystalline Ni and CrO powders with coherent scattering regions of 59 nm and 90 nm respectively is formed. It is demonstrated that thermal decomposition products consist of pseudomorphic particles that inherit the sizes and shapes of initial [NiEn]CrO single crystals. [ABSTRACT FROM AUTHOR]

A structural study was performed by high temperature x-ray diffraction on samples of the filled skutterudite Sm β (Fe α Ni 1- α ) 4 Sb 12 between 303 K and 773 K, i.e. in the range including the highest values of the dimensionless figure of merit ZT for this system. Samples were prepared by direct reaction of the pure elements at 1223 K, followed by an annealing treatment at 873 K. Morphology and composition of the obtained alloys were checked by SEM-EDS; the coefficient of thermal expansion (CTE) was calculated from the refined values of the cell parameter, and its trend as a function of the Fe amount revealed a discontinuity in proximity of the composition separating p - and n -skutterudites. Since the reduction of thermal stresses is a fundamental requirement for the lengthening of the thermoelectric devices lifetime, this evidence suggests useful hints for the choice of the most proper skutterudite compositions to be used in p - and n -legs. The effect of increasing temperature on other structural parameters, such as the shape of the Sb 4 rings, is considered too and discussed in terms of filling degree of the cell. [ABSTRACT FROM AUTHOR]

From crystal chemistry rationale and geometry optimization onto ground state structures with DFT-based computations, a novel ultra-hard body-centered tetragonal C 4 (tet-C 4) is proposed as the simplest dense carbon allotrope. tet-C 4 is identified as cohesive as diamond, and likewise built of corner sharing C4 tetrahedra in all directions. Qualified as mechanically stable from the elastic constants combinations, tet-C 4 has Vickers hardness identical to that of both cubic and hexagonal (lonsdaleite) diamond. Dynamical stability of tet-C 4 derived from all positive phonon bands also allows obtaining heat capacity close to the experimental data of diamond. The electronic band structure shows insulating tet-C 4 with a large indirect band gap of 5 ​eV. Entropy S and specific heat at constant volume C V of tetragonal tet- C 4 as functions of temperature. Experimental data for diamond are shown as gray symbols. [Display omitted] • Body-centered tetragonal C4 (tet-C4) is proposed as simplest dense carbon allotrope. • tet-C4 is mechanically and dynamically stable, and as hard as diamond. • Calculated entropy and heat capacity of tet-C4 are close to the experimental data for diamond. [ABSTRACT FROM AUTHOR]

Acyclic tetraazametal gold(III) perrhenate complex [Au(CHN)](ReO) is synthesized. The 3D crystal structure of the complex is stabilized by weak secondary interactions (N-H...O, C-H...O, С-H...Au hydrogen bonds, and Au...O contacts). The translation sublattice method shows that the motif of the mutual arrangement of cations can be considered to be pseudohexagonal. The product of the thermal decomposition of [Au(CHN)](ReO) in a hydrogen atmosphere is a mixture of nanocrystalline phases (HCP phases based on Re and Au) with the coherent scattering region of 24 nm and 34 nm, respectively. [ABSTRACT FROM AUTHOR]

Novel ultra-hard carbon allotropes are proposed based on crystal chemistry rationale and geometry optimization onto ground state structures. Like diamond, new orthorhombic, tetragonal, and trigonal C 6 are identified as cohesive networks of C4 tetrahedra illustrated by charge density projections exhibiting sp3-like carbon hybridization. The three allotropes are mechanically (elastic constants) and dynamically (phonons) stable. Furthermore, they exhibit thermal properties like those of diamond. The electronic band structures are characteristic of insulators with large band gaps of 5 eV. From four different models evaluating Vickers hardness, the new carbon allotropes are identified as ultra-hard with H V close to 98 GPa, a magnitude characterizing diamond. [Display omitted] • Crystal chemistry devising of new three dimensional carbon structures. • The novel three C6 allotropes resemble diamond. • Similar mechanical properties to diamond are obtained. • Phonons band structures indicate dynamical stability of the three allotropes. • The electronic band structures show large band gaps like diamond. [ABSTRACT FROM AUTHOR]

Novel trigonal BC 11 is reported from extended carbon network diamond-like C 12 hosting boron based on crystal chemistry rationale and geometry optimization onto ground state structure within the density function theory DFT. From charge density projections, while C 12 is identified as a covalent tetrahedral carbon network, BC 11 shows a stacking of C C covalent substructure blocks separated by B C ones with resulting metallic like global behavior. From the elastic constants, h-BC 11 is identified as mechanically stable with large bulk B and shear G moduli: B(BC 11) = 405 GPa; G(BC 11) = 414 GPa versus diamond-like C 12 characterized by higher magnitudes: B(C 12) = 455 GPa and G(C 12) = 552 GPa. Both were found dynamically stable from the phonons band structures which exhibit positive frequencies and highest ones at ω ~ 40 THz, close to diamond. Thermal properties reporting temperature change of the entropy and the heat capacity show close similarity with diamond. While large band gap insulating behavior characterizes C 12 , with E Gap ~ 4.5 eV, the electronic band structure of BC 11 is metallic with boron p-weighted bands crossing the Fermi level as also detailed with the electronic density of states DOS. The results let suggest that BC 11 is a good model structure of heavily doped diamond. [Display omitted] • Crystal chemistry devising of trigonal BC11 • Lowest doping ratio of B obtained in bulk diamond from extended C12 • BC11 has mechanical properties close to diamond • Phonons band structures indicate dynamical stability of both BC11 and pristine C12. • Thermal poperties with entropy and C(V) changes with Temperature • The electronic structures show large band gap for C12 and boron states crossing the Fermi level in BC11. [ABSTRACT FROM AUTHOR]

Crystal structure of a complex salt [CoEn](WO)·6HO is determined by X-ray crystallography. Powder X-ray diffraction is applied for the phase identification of the products of thermal decomposition of the salt in the helium atmosphere. [ABSTRACT FROM AUTHOR]

By single crystal X-ray diffraction the crystal structure of a series of [ M(NH)Cl]WO ( M = Cr, Rh) complex salts is determined. The features of thermal expansion of the single crystal of [Cr(NH)Cl]WO are studied by low- and high-temperature X-ray diffractometry in the temperature range from −173°C to +127°C. It is shown that with an increase in the temperature, W-O distances and ∠O-W-O bond angles equalize and the average W-O distances decrease by 0.012 Å. The thermal properties of the salts in different gaseous atmospheres are examined and the phase composition of the obtained products is studied. [ABSTRACT FROM AUTHOR]

The crystal structure of double complex salt [Pt(NH)Cl][ReCl]Cl·HO is determined. Crystallographic characteristics are: a = 23.9502(4) Å, b = 7.5963(1) Å, c = 8.9016(2) Å, V = 1619.49(5) Å, space group Pnma, Z = 4, d = 3.150 g/cm. The packing of structural fragments is studied. It is shown that on heating the salt in a helium atmosphere up to 840 °C a mixture of two solid solutions of fcc PtRe and hcp PtRe forms. [ABSTRACT FROM AUTHOR]

The crystal structure of [Co(NH)](WO)Cl complex salt is determined by single crystal X-ray. The thermal properties are examined, and the products obtained on heating the salt in different gaseous atmospheres are analyzed by powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

The crystal structure of a double complex salt of the composition [Au(en)][Cu(CO)]·8HO (en = ethylenediamine) at 150 K is determined by single crystal X-ray diffraction. The crystal data for CHAuCuNO are: a = 9.1761(3) Å, b = 16.9749(6) Å, c = 13.4475(5) Å, β = 104.333(1)°, V = 2029.43(12) Å, P2/ c space group, Z = 2, d = 2.450 g/cm. It is demonstrated that the thermal decomposition of the double complex salt in a helium or hydrogen atmosphere affords the solid solution AuCu. [ABSTRACT FROM AUTHOR]

Crystal structures of [Co(NH)Cl]MoO and [Co(NH)Cl]WO complex salts are determined by single crystal X-ray diffraction. It is demonstrated for both salts that within the temperature range T = −123−20°C there is a negative thermal expansion (about 0.26%) towards the c axis of the orthorhombic unit cell ( Pnma space group). Thermal properties of the salts are investigated. The phase composition of the products obtained on heating the salts in different gas atmospheres is studied. [ABSTRACT FROM AUTHOR]

The crystal structure of Na[ReCl]·6HO is determined. The crystallographic characteristics are as follows: a = 6.6955(2) Å, b = 7.0926(2) Å, c = 8.3667(3) Å; α = 102.567(1)°, β = 98.853(2)°, γ = 107.236(1)°; V = 360.08(2) Å, P-1 space group, Z = 1, d = 2.550 g/cm. The thermal properties of Na[ReCl]·6HO are studied in the hydrogen atmosphere. During the thermolysis of Na[ReCl][PtCl]·6HO double complex salt in the hydrogen atmosphere, RePt nanocrystalline solid solutions were obtained. [ABSTRACT FROM AUTHOR]

Complex salts [Ir(NH)Cl]x[Rh(NH)Cl]MO ( x = 0.5, 1; M = Mo, W) are synthesized and their thermal properties are studied. The crystal structures are determined for [Ir(NH)Cl]WO and [Ir(NH)Cl]MoO. In the structures, the ions are linked by N-H...O hydrogen bonds, the shortest ones being 2.868(2)-3.422(2) Å. and 2.860(4)-3.434(3) Å. respectively. The thermal properties of the complex salts are studied in the hydrogen atmosphere and in hydrogen-helium mixtures. It is demonstrated that the final products are the mixtures of nanocrystalline powders of Ir and binary or ternary solid solutions with the hcp lattice. [ABSTRACT FROM AUTHOR]

Two crystalline modifications of a new [Au(dien)Cl](ReO4)2 complex are studied. The geometric characteristics of the [Au(dien)Cl]2+ complex cations are compared, and the way of additional coordination of gold atomos is considered. The thermal properties of the compound are studied in the inert and reducing atmospheres, and for the first time the possibility of the formation of Au0.1Re0.9 solid solution based on the hcp lattice of Re is shown. [ABSTRACT FROM AUTHOR]

In this manuscript the crystal structure of Li 3 UF 7 from powder X-ray and neutron diffraction studies is reported. The existence of Li 3 UF 7 has been debated for a long time, as it is often missed in a number of phase diagram studies. This study adopted a judicious composition of LiF and UF 4 , and an optimum cooling rate to prepare Li 3 UF 7. The Li 3 UF 7 phase could be obtained by cooling the molten LiF-UF 4 with large excess of LiF at a rate of 5 K/min while slower cooling tends to form LiUF 5. The crystal structures of Li 3 UF 7 and LiUF 5 in the temperature range of 300–10 K have been obtained from the powder neutron diffraction studies. At 300 K, Li 3 UF 7 has an orthorhombic lattice with unit cell parameters: a = 8.698(2) Å, b = 8.692(2) Å, c = 12.803(1) Å, V = 968.0(4) Å3; Z = 8 (Space group: C cca), and is isostructural to orthorhombic Li 3 ThF 7. On cooling, the orthorhombic distortion of Li 3 UF 7 increases but does not reveal any structural transition down to 10 K. The crystal structure of Li 3 UF 7 is built from the defective (Li-deficient) layers of edge shared octahedral LiF 6 and layers corner connected UF 9 polyhedra. Analogous studies on LiUF 5 have also been carried out, which has a tetragonal (Space Group: I 4 1 /a) lattice with unit cell parameters: a = 14.8882(8) Å, c = 6.5438(7) Å, V = 1450.5(2) Å3; Z = 16. The structure of LiUF 5 is built from the three-dimensional sub -lattice formed by U 4 F 30 units and the empty tunnels of the sublattice are occupied by Li 4 F 16 clusters formed by four edge shared LiF 6 octahedra. Also, the details of crystal chemistry of the compounds in LiF-UF 4 systems and their thermal stabilities are discussed. The complexity in the crystal chemistry in LiF-UF 4 system is manifested in multiple close by thermal events in the DTA runs which has also been discussed in the manuscript. ga1 • Synthesis and crystal structure of metastable Li 3 UF 7 in LiF-UF 4 are reported. • Conditions for formation of different phases in LiF-UF 4 system are delineated. • Crystal structures of Li 3 UF 7 and LiUF 5 down to 5 K are studied by LT-PND. • Anisotropic thermal expansion in Li 3 UF 7 is observed in between 5 and 300 K. • LiF-UF 4 phase diagram and comparative crystal chemistry phases in it are discussed. [ABSTRACT FROM AUTHOR]