Artículos (Física de la Materia Condensada)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10869

Examinar

Mostrando 1 - 20 de 659

The Crystal and Molecular Structure of 2-Formylpyridine Selenosemicarbazone
(International Union of Crystallography, 1972) Conde Amiano, Alejandro; López Castro, Amparo; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The structure of 2-formylpyridine selenosemicarbazone, SeN4CTH8, has been determined from threedimensional X-ray photographic data. The crystals are monoclinic, space group P2t/e, with unit-cell dimensions a=9.320, b=6-524 and c= 16-275 ,&, fl=90.53 °. There are four formula units in the cell. The structure was solved by the two-dimensional minimum Patterson function and the heavy atom method. It was refined by a full-matrix least-squares method to a final residual R value of0.11 for 1180 observed reflexions. The Se-C bond length of 1.83 ,~ possesses only partial double-bond character. The molecules are linked by N-H...Se hydrogen bonds to form dimer-like units, which are held together by N-H...N hydrogen bonds.
The Crystal Structure and Molecular Conformation of 3,7-Dichlorophenoselenazine
(International Union of Crystallography, 1974) Bernier, F.; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The crystal structure of SeC12NCI2H7 has been solved by Patterson and Fourier methods and refined to an R of 7-5 % by full-matrix least-squares methods. The unit cell is orthorhombic, with a-- 7-995 (3), b = 23.808 (1), c = 6.028 (2)/~, and four molecules in the cell. The space group is Pnma. The structure contains layers of molecules centred on the mirror planes at b/4 and 3b/4.
The Crystal and Molecular Structure of 1-p-Chlorophenyl-4-(tt-a-erythrofuranosyl)-4-imidazoline-2-thione
(International Union of Crystallography, 1974) Pérez Garrido, Simeón; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The title compound, CISOsN2C~sH~3, the definitive formula of which has been established by X-ray structural analysis, is orthorhombic, space group P2~2121 with a= 7.806 (5), b= 29.417 (13) and c= 5-921 (5) A, Z--4. The structure has been solved by direct methods with MULTAN and refined anisotropically (R=0"073) by a method of block-diagonal least-squares with 861 independent reflexions measured on a diffractometer (Cu Ke radiation). The dihedral angle between the phenyl and imidazoline rings is 50 °. The furanose ring is puckered so that C(10) deviates from the mean plane through the other sugar-ring atoms and the dihedral angle between the imidazoline and the furanose rings is 95 °. The packing of the structure is effected by hydrogen bonds.
Molecular Packing in Crystals of Phenoselenazine
(International Union of Crystallography, 1976) Villares Durán, María del Pilar; Jiménez Garay, Rafael; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The crystal structure of phenoselenazine was solved by molecular-packing analysis. Trial models of the rigid molecule were oriented and positioned in the Cheshire cell. The refinement was carried out by structure-factor least-squares calculations using individual anisotropic temperature factors. The final discrepancy index was R = 0.051 for 601 reflexions which were more than two standard deviations above background. The unit cell with a= 7.829 (5), b = 20.909 (4) and c= 5.927 (7)/~ contains four molecules. The space group is P2~2121. The molecule has the same folded configuration as phenothiazine but is more open. The dihedral angle is 149"6 ° .
The Crystal and Molecular Structure of 4-Formylimidazoline-2-thione
(International Union of Crystallography, 1977) Conde Amiano, Alejandro; Moreno, E.; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The title compound is monoclinic, space group P2 Jc, with a = 4.020 (4), b = 21.491(3), c = 7-410 (4) ,4,, fl = 124.1 (5) °, Z = 4. The structure was solved by Patterson-function and heavy-atom methods from diffractometer X-ray data. The final R value is 0.040. All the atoms lie approximately on the least-squares plane of the imidazoline ring. The molecules related by the glide plane are linked by N-H... O hydrogen bonds (2.840 ,~) to form a chain along e. The chains are held together by N-H... S hydrogen bonds (3.260 A) between the molecules related by an inversion centre.
Fluage de monocristaux de NiO
(European Physical Society (EPS), 1978) Cabrera Cano, J.; Domínguez Rodríguez, Arturo; Márquez Delgado, Rafael; Castaing, Jean; Universidad de Sevilla. Departamento de Física de la Materia Condensada
NiO single crystals have been subjected to constant-load compressive creep along (100). Stresses between 50 MPa and 120 MPa and temperatures between 950 °C and 1 200 °C were studied. The activation energy observed suggests that oxygen diffusion is the rate-controlling process.
The Conformation and Crystal Structure of meso-2,10-Dimethyl- 3,1 l-dimethoxycarbonyl- 1,6,9,13-tetraoxadispiro[4.2.4.2]tetradeca-2,10-diene
(International Union of Crystallography, 1979) Conde Amiano, Alejandro; Moreno, E.; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The crystal and molecular structure of the title compound, C16H20Os, has been determined by singlecrystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2t/c with two molecules in a cell of dimensions a = 9.199 (1), b = 12.423 (1), c = 8.047 (1) A, and fl = 114.87 (1) °. The structure was solved by direct methods (MULTAN). Full-matrix least-squares refinement gave a final agreement index of R = 0.054 for 1166 observed reflections. The sixmembered ring adopts the chair conformation around a symmetry centre. The conformation of the fivemembered rings is nearer to a twist than to an envelope, the approximate twofold axis passing through the C(4) atom. The endocyclic C-O bonds are asymmetric and the C=C distance is longer than expected for a double bond. Crystal packing is due to van der Waals interactions only.
The Structure of l-Phenyl-4,5-(l,2-D-glucofurano)imidazolidin-2-one
(International Union of Crystallography, 1980) Conde Amiano, Alejandro; Bernier, F.; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The crystal structure of Cl3Ht6N20 5 has been solved by direct methods. Crystal data are a -- 9.033 (1), b -- 10.097 (1), c -- 7.155 (1)A, fl= 105.92 (1) °, Z -- 2, space group P21 (from statistics). The final R value for 1246 independent reflexions was 0.068. The glucofurano- imidazolidine group adopts a cis form of coupling with a dihedral angle of 70.2 (6) °. The phenyl substituent forms a dihedral angle of 15.1 (6) ° with the imidazolidine ring plane. Intermolecular hydrogen bonds link molecules related by a screw axis to give helical chains parallel to b.
Structure and Molecular Conformation of l-(4-Acetyl-5-methyl-2-furyl)- 1,3-dideoxy-3-nitro-fl-D-xylopyranose
(International Union of Crystallography, 1980) Conde Amiano, Alejandro; Moreno, E.; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
The crystal structure of C I2HIsNO7 has been determined at room temperature. Crystals are tetragonal, space group P432~2, Z = 8, with a -- 12.039 (1), c = 17.979 (4)A. 1304 observed reflexions contributed to the full-matrix least-squares refinement to give R -- 0.075. The pyranose ring displays a slightly distorted chair with 4C~ conformation and all the substituents (furanose ring, NO 2 and OH groups) are equatorial. The reported configuration can be considered as the absolute configuration from the absence of epimerization at the anomeric atom. The packing of the structure can be described by a three-dimensional hydrogen-bonding scheme.
Plastic deformation of CoO single crystals
(EDP Sciences, 1980) Castaing, Jules; Spendel, M.; Philibert, Jean; Domínguez Rodríguez, Arturo; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Constant strain rate compressions along < 001 > have been performed on CoO single crystals (ε ∼ 6 x 10-5 s-1). Yield stresses and work hardening rates have been measured between 77 K and 1 400 K; CoO is very strong when compared to similar compounds. Vickers indentations have been performed on { 100 }, { 110 } and {111 } faces around the Néel temperature, i.e. between 0 °C and 40 °C. Hardness values are low if compared to constant strain rate deformation characteristics; they show a minor anomaly at the Néel temperature.
Kinetics of desorption from a heterogeneous surface
(American Institute of Physics Publising LLC, 1982) Córdoba Zurita, Antonio; Luque Palomo, José Juan; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Mathematical equations governing kinetics of desorption from heterogeneous surfaces are derived from a master equation with the assumption that only nearest-neighbor adatoms interact. A number of cases are analyzed: random, periodical, and patchwise distributions of sites characterized by different activation energies. In general, the kinetic equations obtained must be solved numerically. We have performed numerical calculations for several specific cases and analyzed the influence exerted by heterogeneity and lateral interaction between adatoms on the desorption rate ds-dT. The results obtained make it clear that, due to lateral interaction, the desorption curves are very sensitive to the way in which heterogeneities are distributed on the surface (periodically, patches with different sizes, etc.).
Deformation of MgO by Vickers microindentation tests
(EDP Sciences, 1982) Giberteau, F.; Domínguez Rodríguez, Arturo; Márquez Delgado, Rafael; Castaing, Jules; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Vickers microhardness tests have been performed at room temperature on (100), (110), and (111) MgO faces for various orientations of the pyramid diagonal. The indentations may be deformed probably because of cracking. Comparisons have been made with NiO and CoO which have the same crystal structure, but different plastic and fracture properties. One must be cautious when considering hardness anisotropy which is usually explained by plastic deformation. Dislocation rosette anisotropy is small, but inconsistent which that of hardness. The change of hardness with crystallographic faces in MgO, NiO and CoO cannot be uniquely described.
Structure of l'-(p-Bromophenyl)-3'-ethyl- 1',3', 4',5'-tetrahydro- 1,2-dideoxy-D-glycero- L-gluco-heptofuranoso[ 1,2-d]imidazole-2'-thione,* C16H21BrN205 S
(International Union of Crystallography, 1983) Estrada de Oya, María Dolores; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
M,=433.3, orthorhombic, P2,2~2,, a= 8.466 (2), b .... 27. 136 (5), c - 7.776 (5) A, V = 1786(1)A3, Z=4, D,,,= 1.60(l),Dx= 1.61Mgm -3, Mo Ka, 2 = 0.7107 A, a = 2.42 mm-', F(000) = 888, 300 K, R =0.045 for 1 196 observed independent reflexions. The sugar ring adopts a 4T 3 conformation and the dihedral angle in the bicycle is 72-2(4) ° . Intermolecular hydrogen bonds link molecules related by a screw axis to give helical chains parallel to 1001 I.
Pure diffusional creep of NiO polycrystals
(European Physical Society (EPS), 1983) Jiménez Melendo, Manuel; Cabrera Cano, J.; Domínguez Rodríguez, Arturo; Castaing, Jules; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Compressive creep testing of polycrystalline NiO has been performed in air and argon, at temperatures between 1 100 and 1 500 °C (0.61 to 0.79 TM) under loads corresponding to initial applied stresses from 6 to 90 MPa. Nabarro creep was observed in the lower stress range; creep rate and oxygen diffusivity show a good correlation.
Structure of 4-(~-D-Erythrofuranosyl)-3-methyl- l-(p-tolyl)-4-imidazoline-2-thione Monohydrate, C 15H18N203S.H20
(International Union of Crystallography, 1983) Criado Vega, Alberto; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Mr=324.4, orthorhombic, P212t2 ~, a= 32.150(5), b=10.215(1), c=4.805(1)A, V= 1578.0 (4)/~3, Z = 4, D x = 1.36 Mg m -a, 2(Cu Ka) = 1.5418A, #=1.953mm -1, T=300K, final R= 0.050 for 1361 observed [I>2tr(I)] independent reflexions. The sugar ring adopts a conformation intermediate between envelope 2E and twist 2T forms. The orientation of the imidazoline ring with respect to the furanose is anti; the glycosidic angle is 24.6 (7) °. The crystal packing is due to hydrogen bonds involving the hydration water molecules.
Lattice-Energy Calculations on Phenothiazine and Phenoselenazine Modifications
(International Union of Crystallography, 1983) Estrada de Oya, María Dolores; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Lattice-energy calculations in the atom-atom potential approach have been performed for observed and isostructurally derived hypothetical forms of phenothiazine and phenoselenazine compounds. Energy minimizations with respect to cell constants and molecular rigid-body coordinates lead to absolute minima of energy surfaces in all cases. The experimental values of cell constants for the three observed structures are reproduced to better than 5% and the shifts of positional and orientational molecular parameters are lower than 0.1 A and 2 °, respectively
Lattice Dynamics and Thermal Crystallographic Parameters in Phenothiazine
(International Union of Crystallography, 1984) Criado Vega, Alberto; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
A computer program has been developed to study the lattice dynamics of molecular crystals in the harmonic approximation with the external Born-yon KS.rm~n formalism and an atom-atom potential function. Dispersion curves are obtained for monoclinic phenothiazine together with frequency distribution functions and external mode contribution to thermodynamic functions. Lattice dynamical T, L and S rigid-body tensors are obtained and individual thermal tensors are compared with experiment. The disagreement with respect to experimental results is of the same order as the disagreement with a Schomaker-Trueblood fit of experimental data.
Structure of l'-(p-Bromophenyl)-3'-ethyl- 1',3t,4',5 t -tetrahydro- 1,2-¢~• deoxy-D-glyeero-Dgu/ a-heptofuranoso[ 1,2-d]imidazole-2'-thione,* C16H21BrN2OsS
(International Union of Crystallography, 1984) Estrada de Oya, María Dolores; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
M r = 433.3, monoclinic, P21, a = 6.924 (3), b=8.661 (1), c=15.039(3)A, #=96.92(3) ° , v= 895.3 (4) A a, Z= 2, D, = 1.598 (5), Dx= 1.607 Mg m -a, Mo Ka, 2 = 0.7107/k, # = 2.42 mm -1, F(000) = 444, T = 300 K, R = 0.039 for 2038 observed independent reflexions. The sugar ring adopts a 4E conformation and the dihedral angle in the bicycle is 49.0 (2) °. Intermolecular hydrogen bonds link the molecules to form a three-dimensional network.
Structure of l-(p-Ethoxyphenyl)-1,3-dihydro-3-phenyl-2H-benzimidazole-2-thione, C2IHlaN2OS
(International Union of Crystallography, 1984) Criado Vega, Alberto; Conde Amiano, Alejandro; Márquez Delgado, Rafael; Universidad de Sevilla. Departamento de Física de la Materia Condensada
Mr=346-4, orthorhombic, P212121, a= 7.600(1), b= 11.132(2), c=20.767 (3)A, v= 1756.9(5)A 3, z=4, Dx=1.31Mgm -3, 2(CuKct) =.1.5418/k, /~= 1.67mm -1, F(000)=728, T= 300 K. Final R = 0.049 for 1531 observed independent reflections. The benzimid~zole bicycle is quasi-planar, the dihedral angle between the two fused rings being 1.6 (2) °. The unsubstituted phenyl ring is planar while the phenyl ring with the ethoxy substituent deviates significantly from the expected planar conformation.
Mechanism of surface dehydration of anatase (TiO2)
(American Institute of Physics Publising LLC, 1985) Córdoba Zurita, Antonio; Luque Palomo, José Juan; Universidad de Sevilla. Departamento de Física de la Materia Condensada
A comparative study of the dehydration of the (001) and (111) surfaces of TiO2 (anatase) has been made starting from a master equation and introducing suitable transition probabilities. From the experimental data considered, relative to sample Degussa P25 of Munuera and co-workers, it is concluded that the (111) face is the most likely to be exposed. The detailed mechanism of dehydration is analyzed and an estimate of the values of activation energies and frequency factors is presented. This analysis makes it clear that the surface migration of protons plays an important role during the dehydration process. Also the influence on the degree of surface hydration, the dehydration rate, and the numbers of certain ionic groups on the surface exerted by the temperature rate in a linear heating program and by initial surface coverage are discussed.

Examinar

Examinando Artículos (Física de la Materia Condensada) por Fecha de publicación