Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

The non-isothermal devitrification of Na₂O · 2 CaO · 3 SiO₂ glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T_m, and the activation energy values, E_c, for crystal growth.The temperature, T_m=580°C, is very close to the glass transition temperature, T_g=570°C, and the value of E_c=78 Kcal mole^?1 for the surface crystal growth is nearly the same as the value E_c=89 kcal mole^?1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.     

Preparation,crystal structure,and properties of HgSnP14 and other polyphosphides with HgPbP14-type structure

The new compound HgSnP₁₄ and the known isotypic polyphosphides HgPbP₁₄ and MM′P₁₄ (M = Zn, Cd; M′ = Sn, Pb) were prepared by reaction of the elemental components in evacuated silica tubes. They are diamagnetic semiconductors with bandgaps ranging from 0.4 ± 0.2 eV for HgPbP₁₄ to 1.6 ± 0.1 eV for ZnSnP₁₄. The crystal structure of CdSnP₁₄ was refined from single-crystal X-ray counter data to a residual of R = 0.040 for 83 variable parameters and 1182 structure factors. The crystal structure and physical properties of these polyphosphides are briefly discussed.     

Enantiodivergent formation of a chiral cytosine crystal by removal of crystal water from an achiral monohydrate crystal under reduced pressure

An achiral nucleobase cytosine forms an achiral monohydrate crystal (space group: P2₁/c) by crystallization from a water solution. It was found that the removal of crystal water under reduced pressure at room temperature afforded a chiral crystal of anhydrous cytosine (P2₁2₁2₁). The crystal chirality of anhydrous cytosine corresponds to the enantiotopic crystal face of the achiral monohydrate; therefore, when the enantiotopic b¹-face is exposed to the reduced pressure, dehydration occurred in the direction from the b¹-face to provide [CD(+)310_KBr]-cytosine crystal. In contrast, dehydration from the b²-face gave the opposite enantiomorphous [CD(?)310_KBr]-cytosine crystal. The correlation between enantiotopic faces and the formed crystal chirality is opposite to that from dehydration by heating. The formed chiral cytosine crystals act as a chiral trigger for asymmetric autocatalysis with enantioenrichment amplification of pyrimidylalkanol.     

Infrared polarised spectrum of bis-(dimethyldithiophosphato)nickel(II)

The polarisation behaviour of the infrared absorptions of a single crystal of bis-(dimethyldithiophosphato) nickel(II) with (001) as the predominant face is studied. Because only a and b polarisation can be measured on (001), the b_2u and b_3u normal modes, which are polarised on b, cannot be distinguished, whilst the b_1u modes are observed on a. The most characteristic absorptions of the compound are assigned on the basis of the polarisation results. The comparison of the crystal with the solution spectrum indicates that the absorptions at 396 and 357 cm^?1 undergo crystal field splitting in the solid.     

Temperature behavior of the protonic conductor K4LiH3(SO4)4

The results of the X-ray structural study for the K₄LiH₃(SO₄)₄ single crystal are presented at a wide temperature range. The thermal expansion of the crystal using the X-ray dilatometry and the capacitance dilatometry from 8 to 500 K was carried out. The crystal structures data collection, solution and refinement at 125, 295, 443 and 480 K were performed. The K₄LiH₃(SO₄)₄ crystal has tetragonal symmetry with the P4₁ space group (Z=4) at room temperature as well as at the considered temperature range. The existence of a low-temperature, para-ferroelastic phase transition at about 120 K is excluded. The layered structure of the crystal reflects a cleavage plane parallel to (001) and an anisotropy of the protonic conductivity. The superionic high-temperature phase transition at T_S=425 K is isostructural. Nevertheless, taking into account an increase of the SO₄ tetrahedra libration above T_S, a mechanism of the Grotthus type could be applied for the proton transport explanation.     

Palladium site ordering and the occurrence of superconductivity in Bi2Pd3Se2−xSx

The crystallographic and electronic structures of compounds related to parkerite (Bi₂Ni₃S₂) are investigated with respect to the recently reported occurrence (Bi₂Pd₃Se₂) and absence (Bi₂Pd₃S₂) of superconductivity. Similarities and differences of the crystal structures are discussed within the series of solid solutions Bi₂Pd₃S_2−xSe_x from powder and single crystal diffraction data. From crystal structure refinements, the question of different structures and settings of parkerite is discussed. Similar and different 2D and 3D partial Pd-Ch (Ch=S, Se) structures are related to half antiperovskite ordering schemes. To investigate the relation of low dimensional structures and the occurrence of superconductivity, electronic structures are analyzed by scalar-relativistic DFT calculations, including site projected DOS, ECOV and Fermi surfaces.     

The mechanism of the magnetic interaction in the β phase of the p-(nitro)phenyl nitronyl nitroxide (KAXHAS). A bottom-up study using only ab initio data

The magnetism of the β phase of p-(nitro)phenyl nitronyl nitroxide (KAXHAS) crystal has been studied using a recently developed theoretical approach ‘J. Phys. Chem. A 106 (2002) 1299’. This approach is a bottom-up study based on the evaluation of the magnetic interaction between all pairs of radicals (J_AB), which allows the definition of the magnetic structure of the crystal. With only such knowledge, one solves an algebraic Heisenberg Hamiltonian on a properly chosen finite subset of the magnetic structure and then computes the magnetic susceptibility χ(T) and/or heat capacity C_p(T) curves for the crystal. This method is applied here to the KAXHAS crystal. The theoretical χ(T) and C_p(T) results are in very good agreement with the available experimental data. This theoretical methodology is first reviewed here on physical terms, and then used to rationalize the bulk ferromagnetic behavior of KAXHAS in terms of its corresponding microscopic J_AB pair interactions.     

Three new tellurite halides with unusual Te coordinations and iron honeycomb lattice variants

The crystal structure of three new iron and copper-iron tellurite halides are presented; (I) Cu₃Fe₈Te₁₂O₃₂Cl₁₀ that crystallizes in the orthorhombic space group Pmmn, (II) Fe₈Te₁₂O₃₂Cl₃Br₃ that crystallizes in the monoclinic space group P2₁/c, and (III) Fe₅(TeO₃)₆Cl₂ that crystallizes in the triclinic space group P-1. The crystal structures were solved from single crystal X-ray diffraction data. All three compounds have layered crystal structures where the Fe atoms form variants of the honeycomb lattice. Highly unusual Te⁴⁺ coordination polyhedra are exemplified: [TeO₃₊₁E], [TeO₃XE], [TeO₃₊₁XE], and [TeO₃X₂E] (X=halide ion, E=the lone-pair valence electrons). The crystal structures contain large non-bonding volumes occupied by the stereochemically active lone-pair electrons on Te⁴⁺.     

Synthese et structure du sulfate double MSbF2SO4 (M = Rb,Cs)

The crystal structure of RbSbF₂SO₄ has been determined on a single crystal (R = 0.078 for 710 reflections). The structure shows sulfate anions distorted by the SOSb bonds. The antimony atom is from an SbF₂ unit. This antimony dihalogen is from the family of the $\text{1}\text{1}$ compounds which are in MX₃SbX₃ (M = Al, Ga, In) (X = Cl, Br) systems.     

Infrared and Raman spectra of crystalline para-bromoaniline at low temperatures

The polarization characteristics of the i.r. absorption bands of oriented p-bromoaniline crystal films have been studied at low temperatures. Raman spectra of this compound in solution and in the polycrystalline state have been recorded as an aid to the vibrational assignment of the crystal bands. The vibrational spectra are interpreted to deduce the crystal factor group (D_2h) and the molecular site symmetry (C_s). The observed factor group splittings and dichroic ratios suggest the crystal unit cell of p-bromoaniline to be isostructural with that of p-chloroaniline.     

Effect of water absorption on the plastic deformation behavior of nylon 6

The tensile behavior of nylon 6 films has been investigated in relation to water content. Modification of chain mobility in the amorphous phase via water plasticization appears to have a determining impact on the stress-strain response. More specifically, both yield stress value and hardening behavior over a large strain domain are strikingly equivalent for samples drawn at same ΔT between draw temperature T_d and main amorphous relaxation temperature T_α. This apparent lack of thermal activation of crystal plasticity in the fibrillar transformation suggests that crystal block fragmentation proceeds via H-bond unzipping through water penetration at defective crystal interfaces.     

A novel boron-rich quaternary scandium borocarbosilicide Sc3.67−xB41.4−y−zC0.67+zSi0.33−w

A novel quaternary scandium borocarbosilicide Sc_3.67−xB_41.4−y−zC_0.67+zSi_0.33−w was found. Single crystallites were obtained as an intergrowth phase in the float-zoned single crystal of Sc_0.83−xB_10.0−yC_0.17+ySi_0.083−z that has a face-centered cubic crystal structure. Single crystal structure analysis revealed that the compound has a hexagonal structure with lattice constants a = b = 1.43055(8) nm and c = 2.37477(13) nm and space group (No. 187). The crystal composition calculated from the structure analysis for the crystal with x = 0.52, y = 1.42, z = 1.17, and w = 0.02 was ScB_12.3C_0.58Si_0.10 and that agreed rather well with the composition of ScB_11.5C_0.61Si_0.04 measured by EPMA. In the crystal structure that is a new structure type of boron-rich borides, there are 79 structurally independent atomic sites, 69 boron and/or carbon sites, two silicon sites and eight scandium sites. Boron and carbon form seven structurally independent B₁₂ icosahedra, one B₉ polyhedron, one B₁₀ polyhedron, one irregularly shaped B₁₆ polyhedron in which only 10.7 boron atoms are available because of partial occupancies and 10 bridging sites. All polyhedron units and bridging site atoms interconnect each other forming a three-dimensional boron framework structure. Sc atoms reside in the open spaces in the boron framework structure.     

Heat capacities and related thermal properties of DyNi5, HoNi5 and ErNi5 between 5 and 300 K

Heat capacity data and calculated thermodynamic functions are presented for DyNi₅, HoNi₅ and ErNi₅. λ-type thermal anomalies are noted at 12.0 K (DyNi₅), 4.1 K (HoNi₅) and 8.0 K (ErNi₅). Schottky-type anomalies are observed at higher temperatures. The λ and Schottky anomalies are ascribed to the destruction of ferromagnetic order and to crystal field excitation, respectively. A deficiency of magnetic entropy, compared to Rln(2J + 1), is noted corresponding roughly to Rln2. This suggests that the ground state in the ordered materials is a doublet. ErNi₅ is analyzed using a Hamiltonian containing terms representing the crystal field and magnetic interactions. The analysis shows that a doublet ground state can result with reasonable values of the crystal field parameters. The parameters are shown to be consistent with the heat capacity behavior of ErNi₅. Ordering temperatures are not proportional to the de Gennes function.     

Mise en évidence d'un désordre statistique dans les structures chalcogénoiodures d'étain et d'antimoine

The crystal structures of Sn₂SbX₂I₃, with X = S or Se, and Sn₃SbSe₂I₅ are characterized by a statistical disorder of part of the [Sb] and [Sb, Sn] sites. All these crystal structures are built up from infinite ribbons (Sn₂X₄)_n of SnX₅ pyramids where X = ((S, Se) and I). The ribbons are weakly linked through Sn … I interactions to give infinite sheets. Between sheets are located [Sb] or [Sb, Sn] atoms in twinned sites.     

Interpretation of the crystal field parameters by the angular overlap model - application to some fn electron systems

In this paper, we interpret crystal field parameters in the angular overlap model of Jørgensen, involving σ and π effects. We have studied some trivalent rare earth ions in several compounds: KY₃F₁₀, the aluminates LnAlO₃, LaCl₃ and Ln(OH)₃. In all cases σ effects are dominant; e_σ values decrease as the atomic number of the rare earth ion increases. For the rare earth fluorine bonding the obtained values for e_π are the greatest. It may also be noted that e_σ and e_π parameters are connected with the B₆^m crystal field parameters. Finally, we have shown for several compounds, the existence of a power law especially for σ effects.     

Polarized vibrational,electron absorption and luminescence spectra of Nd(NO3)3(DMSO)4 single crystal

Infrared and Raman spectra of polycrystalline and single crystal Nd(NO₃)₃(DMSO)₄ have been measured. The molecular and crystal structure is analysed in terms of a monoclinic unit cell of C2/c symmetry. A comparison of i.r. spectra measured parallel and perpendicular to the b axis of the unit cell as well as Raman spectra for several tensor elements was used to describe the internal and external optical modes. The optical absorption and luminescence spectra of neodymium nitrate tetra dimethyl sulphoxide single crystal were recorded at 77 and 300 K between 4000–30 000 cm⁻¹. The electronic transitions were assigned to the crystal field splitting manifolds. The band intensity measurements performed for | and ⊥ b polarizations are related to Judd—Ofeld parameters and the anisotropy of these values is discussed.     

Rare earth ions in a hexagonal field IV

Energy levels and eigenfunctions of rare earth ions in a crystal field of hexagonal symmetry have been obtained using a Hamiltonian of the form $\text{H}$ = B°₂O°₂ + B°₄O°₄. Results are presented for all J values appearing in the rare earth series. The order of the energy levels has been determined for all relative values of the second and fourth order crystal field intensity parameters, B°₂ and B°₄. This, of course, includes information for the commercially significant RCo₅ compounds, for which the second order term is dominant. The eigenfunctions are pure M states with permanent magnetic moments ± Mg μ_B. The moments are unchanged by a field applied along the c axis.     

Synthesis and crystal structure of 1D polyoxometalate-based composite compound, [{Gd(NMP)6}(PMo12O40)]n (NMP=N-methyl-2-pyrrolidone)

A novel compound, [{Gd(NMP)₆}(PMo₁₂O₄₀)]_n, has been synthesized and characterized by IR, and UV spectroscopy, and single crystal X-ray structural analysis. It forms an unprecedented one-dimensional zigzag chain built from alternating polyanions and cationic units through Mo-O_t-Gd-O_t-Mo links in the crystal. In the compound, Gd³⁺ is eight-coordinated with a bicapped trigonal prism geometry environment of oxygen atoms. The results of the single crystal X-ray diffraction analyses and IR are agreement and both show the metal cation units are coordinately bonded to the Keggin cluster. The UV spectrum of the title compound suggests that the compound is entirely dissociated in dilute solution.     

La3,5Ru4O13: Un nouveau compose´a`feuillets de type pe´rovskite

The title compound formula, La_3.5Ru₄O₁₃, has been established by means of crystal structure determination. The orthorhombic unit cell has the following dimensions:a = 11.994, b = 5.609, c = 3.856A?. Least-squares refinement using single-crystal intensity data corrected for absorption reachedR = 0.029 for 777 measured independent reflections. La_3.5Ru₄O₁₃ is built up from perovskite-type slabs parallel to (100) which are running throughout the crystal; these three octahedra slabs are linked together by either La atoms or RuO₆ octahedra. The latter are also joined together by opposite edges to form one-dimensional infinite strings parallel to theb-axis. The doubling of thec parameter can be caused by the ordering of these RuO₆ chains and La atoms.