scispace - formally typeset
Search or ask a question

Showing papers on "Orthorhombic crystal system published in 1981"


Journal ArticleDOI
TL;DR: The crystal structure of pyridine is orthorhombic with space group Pna21, a = 1752.4(3), b = 896.9(2), and c = 1135.
Abstract: The crystal structure of pyridine is orthorhombic with space group Pna21, a = 1752.4(3), b = 896.9(2), and c = 1135.2(2) pm at 153 K and Z = 16. A low melting crystalline hydrate of pyridine was found by DTA to be a trihydrate. It is orthorhombic, too, with space group Pbca, a = 1244.4(3), b = 1783.2(6), and c = 679.1(2) pm at 223 K and Z = 8. Both structures were determined from single crystal MoKα diffractometer data and refined to unweighted R values of 0.044 for 2769 and of 0.074 for 932 observed independent reflections. Most apparent in the anhydrous structure is an arrangement of the molecular noncrystallogrpahic twofold axes in layers perpendicular to the c‐axis direction and separated by c/4. With the ring centers not far from the points of a bcc lattice a ’’molecular coordination number’’ of 14 can be assigned to each of the four independent molecules. Their geometries are very similar and close to mm‐C2v symmetry. In the structure of the trihydrate the water molecules are O–H ⋅ ⋅ ⋅ O hydrogen bo...

166 citations


Journal ArticleDOI
TL;DR: In this article, a ternary compound BaNd2Ti3O10 (1:1:3) and a binary compound Nd4Ti9O24 (1 :1:5) have been identified in the BaO Nd2O3TiO2 system.

125 citations


Journal ArticleDOI
TL;DR: In this paper, the crystal structure of Mg51Zn20, a phase designated conventionally as "Mg7Zn3", has been determined by the single-crystal X-ray diffraction method.

92 citations


Journal ArticleDOI
TL;DR: In this paper, the lattice vibration of black phosphorus was investigated under hydrostatic high pressure by polarized Raman scattering, and the crystal structure changes to the rhombohedral A7-structure from the layered orthorhombic structure at 52 kbar.
Abstract: The lattice vibration of black phosphorus was investigated under hydrostatic high pressure by polarized Raman scattering. On applying pressure the crystal structure changes to the rhombohedral A7-structure from the layered orthorhombic structure at 52 kbar. At atmospheric pressure four phonon modes are observed at 362 cm -1 with A g -symmetry, 467 cm -1 A g , 194 cm -1 B 1 g and 439 cm -1 B 2 g . The Gruneisen parameters are 0.74 for the 362 cm -1 A g -mode, 0.10 for the 467 cm -1 A g -mode and 0.22 for the 439 cm -1 B 2 g -mode. The energies of the latter two modes change little with pressure, since in these modes the atoms displace to deform the rigid zigzag chain along the a -axis. In the A7-structure the A 1 g -mode was observed at 466 cm -1 and the E g -mode at 392 cm -1 . The comparison with the phonon modes in other group V materials was made.

89 citations


Journal ArticleDOI
TL;DR: In this paper, the structure change with temperature for Fe100-xBx alloys (x=2~33 at.%B) fabricated by a rapid quenching technique has been carried out by measuring magnetization, electrical resistivity and thermal expansion and also by structural analysis by X-ray diffraction.
Abstract: A study of the structure change with temperature for Fe100-xBx alloys (x=2~33 at.%B) fabricated by a rapid quenching technique has been carried out by measuring magnetization, electrical resistivity and thermal expansion and also by structural analysis by X-ray diffraction. The amorphous alloys with 11x13 at.%B transform into α-Fe(B) around 300°C which has a smaller lattice constant than that of α-Fe. Then α-Fe(B) decomposes into two stable α-Fe and Fe2B at about 450°C. For the amorphous alloys with 14x25 at.%B, the amorphous phase transforms into both α-Fe and tetragonal Fe3B compound at about 400°C. With further heating, an orthorhombic Fe3B compound can be observed clearly in addition to these 2 phases for 17x25 at.%B. For temperatures beyond 600~700°C, they transform to the equilibrium phases of α-Fe and Fe2B compound.

87 citations


Journal ArticleDOI
TL;DR: In this paper, the structure of the title compound has been determined by single crystal X-ray diffraction, and the solvent and temperature dependent solution behavior of this complex has been examined by a combination of 1H, 19F and 31P NMR spectroscopy and conductivity measurements.

72 citations


Journal ArticleDOI
TL;DR: In this paper, the structures of four families of intermetallic compounds are analyzed in terms of the number, sizes, positions, and symmetry properties of tetrahedral interstitial holes.
Abstract: The structures of four families of intermetallic compounds are analyzed in terms of the number, sizes, positions and symmetry properties of tetrahedral interstitial holes. The structure types considered are hexagonal AB5 (D2d), cubic AB2 (C15), hexagonal AB2 (C14) and orthorhombic AB (Bf). Holes and clusters of holes are considered in terms of their suitability for hydrogen occupancy in the formation of intermetallic compound hydrides. In the cases of the hydrides LaNi5H6 and LaCo5H4, the parent hexagonal structure P6/mmm is changed on hydriding to trigonal P31m in the former case and to orthorhombic Cmmm in the latter case. The symmetry changes that correspond to these transformations are shown to be directly related to the amount of hydrogen absorbed; i.e. some potential sites in the parent compound are retained and others are not, depending on the structural change. In those cases where structural data for the hydride phases are not available or where the parent structure does not change on hydriding, it is shown that reasonable estimates of the extent of hydrogen absorption can be made based on the number and the sizes of available holes or hole clusters in the parent compound.

59 citations


Journal ArticleDOI
TL;DR: Part of the Zr-Fe phase diagram between the compounds Zr3Fe and Zr2Fe was determined using X-ray, microstructural and thermal analyses as discussed by the authors.
Abstract: Part of the Zr-Fe phase diagram between the compounds Zr3Fe and Zr2Fe was determined using X-ray, microstructural and thermal analyses The eutectoid equilibrium Zr2Fe Zr3Fe + ZrFe2 was found at about 775 ° C and a peritectoid equilibrium β + Zr2Fe Zr3Fe was determined at about 885 °C Differential thermal analysis was used to determine the temperatures 1 (1) of the peritectic equilibrium L + ZrFe2 Zr2Fe (974 °C) 2 (2) of the eutectoid equilibrium β α + Zr3Fe (830 °C) The crystallographic characteristics of the Zr3Fe compound were determined The crystal system is orthorhombic with unit cell parameters a = 8819 ± 0001 A , b = 3329 ± 0004 A and c = 10952 ± 0002 A , and the number of formula units in the unit cell is 4 The space group is A2122 and the powder pattern was indexed

58 citations


Journal ArticleDOI
TL;DR: In this article, the lattice volume relaxations and energies associated with the formation and motion of Schottky defects in TlCl and TlBr have been determined and the association energy of Tl/sup +/ vacancies and divalent impurities was also determined.
Abstract: Detailed studies of the pressure and temperature dependences of the ionic conductivities of TlCl and TlBr have allowed determination of the lattice volume relaxations and energies associated with the formation and motion of Schottky defects in these crystals. The volume relaxations deduced from the conductivity are found to be comparable in magnitude with values calculated from the strain energy model and a dynamical model. The association energy of Tl/sup +/ vacancies and divalent impurities was also determined for TlBr. A particularly important result is the finding that for these CsCl-type crystals the relaxation of the lattice associated with vacancy formation is outward. Earlier studies on ionic crystals having the NaCl structure have yielded a similar result. This outward relaxation thus appears to be a general result for ionic crystals of both the NaCl and CsCl types (and possibly other ionic lattice types), in disagreement with earlier theoretical calculations which show that the relaxation should be inward for all models of ionic vacancies investigated. The conductivity of TlI was studied in both the (low temperature and pressure) orthorhombic phase as well as in the cubic CsCl-type phase. There is a large electronic contribution to the conductivity in the orthorhombic phase. Anmore » interesting result for all three materials is the observation in the cubic phase of a pressure-induced transition from ionic to electronic conduction. This is in qualitative agreement with what is known about the pressure dependences of the electronic structure of these materials.« less

53 citations


Journal ArticleDOI
TL;DR: The crystal structure of a magnesium heptaboride, whose structural formula is Mg2B14, was determined from X-ray powder patterns according to a profile refinement technique and on the basis of isotypism with MgAlB14 as mentioned in this paper.
Abstract: The crystal structure of a magnesium heptaboride, whose structural formula is Mg2B14, was determined from X-ray powder patterns according to a profile refinement technique and on the basis of isotypism with MgAlB14. The symmetry is orthorhombic and the lattice parameters are a = 5.970 A , b = 8.125 A and c = 10.480 A . The refinement is based on the space group Imam. The unit cell contains five non-equivalent boron and two nonequivalent magnesium atoms. The structure consists of chains of B12 icosahedra extending in the direction of the c axis. The chains are linked laterally via inter-icosahedral bonds or BB bonds involving nonicosahedral atoms, thus forming a three-dimensional boron network. The magnesium atoms occupy two types of holes in this network, corresponding to coordination numbers 12 and 16.

51 citations


Journal ArticleDOI
TL;DR: LaTaO 4 as mentioned in this paper is an orthorhombic, space group A 2 1 am, with a = 5.6643(1), b = 14.6411(3), c = 3.9457(1) and Z = 4.6.

Journal ArticleDOI
TL;DR: Anhydrous monoclinic and hydrated orthorhombic uric acid crystals can be nucleated and grown from pure water solutions either separately or together with epitaxial relationships.

Journal ArticleDOI
TL;DR: In this article, a study of the range of thermal stability and phase transitions in the following oxides of antimony: orthorhombic and cubic Sb2O3, orthorHombic Sb 2O4 and cubicSb 2 O5, is presented.

Journal ArticleDOI
TL;DR: Polarized Raman spectra are investigated in GeSe and SnSe at low temperatures as mentioned in this paper, and new Raman lines which can not be expected by a group theoretical analysis for the known crystal structure of the orthorhombic D162h are observed typically in the (a, a) and (b, b) polarization configurations.

Journal ArticleDOI
TL;DR: The crystal symmetry of the reaction product of hydrogen with the intermetallic compound Mg2Ni has been determined to be tetragonal with unit cell dimensions: a=6.533 AA and c=7.499 AA, by in situ X-ray diffractometry at about 623K and under 4.6 MPa hydrogen pressure as mentioned in this paper.
Abstract: The crystal symmetry of the reaction product of hydrogen with the intermetallic compound Mg2Ni has been determined to be tetragonal with unit cell dimensions: a=6.533 AA and c=7.499 AA, by in situ X-ray diffractometry at about 623K and under 4.6 MPa hydrogen pressure. The resultant hydride phase transforms at 503K to an orthorhombic structure with lattice dimensions: a=11.394 AA, b=11.196 AA and c=9.165 AA. This phase transition is of polymorphic type as is evident from the well defined exothermic (endothermic) peak in the pressure-differential scanning calorimetry curves obtained during cooling (heating) after the formation of the nearest stoichiometric hydride Mg2NiH4. The results are briefly compared with previously reported data.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the chemical short-range order (CSRO) of amorphous Zr 3 Fe studied by Mossbauer spectroscopy is similar to the CSRO of metastable crystalline Zr3 Fe formed during crystallization.

Journal ArticleDOI
TL;DR: LiGaSe2 has been shown to have an orthorhombic unit cell structure with an energy band gap of 3.65 eV and melting point was determined by differential thermal analysis to be 846 °C.
Abstract: Single crystals of a new ternary lithium chalcogenide LiGaSe2 were grown by an improved directional solidification technique. The typical as‐grown crystal has dimensions of about 4 mm cubed and shows a transparent light yellow color. We infer that LiGaSe2 crystallizes in the β‐NaFeO2 structure having an orthorhombic unit cell (a = 6.833 A, b = 8.227 A, and c = 6.541 A) by powder x‐ray diffraction. The melting point was determined by differential thermal analysis to be 846 °C. The energy band gap of LiGaSe2 at room temperature was determined by optical reflectance measurements to be 3.65 eV.

Journal ArticleDOI
TL;DR: In this paper, the structure of cubic and orthorhombic phases of K 2 Mn 2 (SO 4 ) 3 was determined at 20°C and -90°C by X-ray diffraction.
Abstract: Structures of cubic and orthorhombic phases of langbeinite-type K 2 Mn 2 (SO 4 ) 3 have been determined at 20°C and -90°C by X-ray diffraction. Thermal parameters of oxygen atoms in the cubic phase are remarkably anisotropic and show unusually high values, whereas those in the orthorhombic phase are rather normal. The change in bond lengths and angles at the transition clarifies a rigid body motion of SO 4 group. It is concluded that the principal structural change at the cubic-orthorhombic transition is characterized by ordering of sulfate groups.

Journal ArticleDOI
TL;DR: In this article, the structure of NH 4 Fe II Fe III F 6 is studied in order to explain further its peculiar antiferromagnetic behavior compared to the spin glass one of the pyrochlore family.

Journal ArticleDOI
TL;DR: The existence of the Pd-Si system was examined in the 13 to 25 at. pct silicon range by X-ray diffraction, thermal analysis, and metallography.
Abstract: The Pd-Si system was examined in the 13 to 25 at. pct silicon range by X-ray diffraction, thermal analysis, and metallography. The existence of the compounds Pd5Si, Pd9Si2, and Pd3Si was confirmed. The three compounds form peritectically. Pd5Si is monoclinic, while Pd9Si2 and Pd3Si are orthorhombic. These compounds form defect structures having low symmetry and large unit cells. Electron concentrations per unit cell govern compound formation. However, there was no evidence of the existence of either Pd4Si or Pd9Si4.

Journal ArticleDOI
TL;DR: In this article, LiAlB14 was grown from a high temperature AlB solution containing a small amount of lithium and the crystals are orthorhombic with a = 5.8469(9) A, b = 8.1429(8) A, c = 10.3542(6) Z = 4 and space group Imam.
Abstract: Crystals of LiAlB14 were grown from a high temperature AlB solution containing a small amount of lithium. The crystals are orthorhombic with a = 5.8469(9) A , b = 8.1429(8) A , c = 10.3542(6) A , Z = 4 and space group Imam. A total of 1871 independent reflections (Mo Kα; 2θ

Journal ArticleDOI
TL;DR: In this paper, the powder patterns of the monoclinic phase and the orthorhombic phase of ferric molybdate were given, and linear equations describing the thermal expansion of the two phases were described.
Abstract: Indexed powder patterns of the monoclinic phase, stable at room temperature, and of the orthorhombic phase, stable for T > 786 K, are given. The cell dimensions are: a = 15.737 (8), b = 9.231 (5), c = 18.224 (9) A, β = 125.46 (2)° at 295 K; a = 9.330 (3), b = 12.868 (5), c = 9.242 (3) A at 818.6 K. Linear equations describing the thermal expansion of the two phases of ferric molybdate are reported. To verify if ferric molybdate can incorporate excess MoO3, measurements on non-stoichiometric samples were also made: no evidence of the presence of excess MoO3 was found.

Journal ArticleDOI
TL;DR: In this article, the Ag2Se films produced by the reaction of vacuum-deposited silver films with amorphous selenium films were investigated by electron microscopy and electron diffraction.

Journal ArticleDOI
TL;DR: In this paper, three allotropic varieties of Mg 2 NiH 4 with monoclinic, orthorhombic and cubic symmetry have been identified and the transition temperature is 245°C at 1 bar.

Journal ArticleDOI
TL;DR: In this paper, the title compound with the formula C5H11O-C6H4-COO-CPPOB has been solved by direct methods and refined to a final R value of 0.050.
Abstract: The title compound with the formula C5H11O-C6H4-COO-C6H4-CN (CPPOB) crystallizes in the orthorhombic space group Pnam with a = 16.465 A, b = 13.577 A, c = 7. 621 A and four molecules per unit cell. The structure has been solved by direct methods and refined to a final R value of 0.050. The CPPOB molecules have exact Cs symmetry as a consequence of their location on crystallographic mirror symmetry planes, the benzene ring to which the cyano group is attatched has a perpendicular orientation to the other ring in the plane. The molecules adopt a nearly optimal stretched form, neighbouring molecules make an angle of 35.2°. The results are discussed in relation to the mesomorphic behaviour of CPPOB.

Journal ArticleDOI
TL;DR: The stannoferrite LiFeSnO 4 has been synthesized and investigated by X-ray diffraction and electron microscopy as discussed by the authors, and two forms have been characterized.

Journal ArticleDOI
TL;DR: In this article, the structural behavior of Ni 10 Zr 7 with copper substituted for nickel was investigated using X-ray diffraction, and the lattice parameter variations were discussed in terms of ordered substitution of nickel atoms by copper atoms.
Abstract: The structural behaviour of Ni 10 Zr 7 with copper substituted for nickel was investigated using X-ray diffraction. All the compounds are isostructural, crystallizing in the Ni 10 Zr 7 orthorhombic structure type. The lattice parameter variations are discussed in terms of ordered substitution of nickel atoms by copper atoms.

Journal ArticleDOI
TL;DR: In this article, single crystals of dihydrodibenzo[b, i]-1, 4, 8, 11-tetraazacyclotetradecinenickel iodide show metallic conductivity between room temperature and approx. 110 K.
Abstract: Single crystals of dihydrodibenzo[b, i]-1, 4, 8, 11-tetraazacyclotetradecinenickel iodide show metallic conductivity between room temperature and approx. 110 K. The crystals are orthorhombic, space group Ibam with four formula units per cell of the following dimensions: a = 20.245, b = 13.416, c = 6.418 A. The analogous palladium complex is isomorphous, the cell constants being a = 20.452, b = 13.430 and c = 6.499 A. A number of other partially oxidized metal tetraaza [14]annulenes also show electrical conductivity.

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of Mn4B was refined using single-crystal X-ray diffractometer techniques and the refinement of a crystal, representing a manganese-rich composition, gave a metal: B atomic ratio insignificantly different from 2:1.
Abstract: The crystal structure of Mn4B was refined using single-crystal X-ray diffractometer techniques. The refinement of a crystal, representing a manganese-rich composition, gave a metal: B atomic ratio insignificantly different from 2:1. The space group adopted was Fddd and the lattice parameters obtained from powder diffraction were a = 14.539 5(8) A , b = 7.2914(11) A and c = 4.2082(3) A . The final index of agreement, R(F2), was 2.9%.

Journal ArticleDOI
TL;DR: The crystal structures of Eu2B5O9X (X=Cl and Br) were determined by the method of X-ray diffraction analysis and refined by the least-square method to give R=0.054 for 1967 observed reflections of eu2b5O 9Cl and R= 0.047 for 1979 observed reflections from Eu 2b5o9Br as discussed by the authors.
Abstract: The crystal structures of Eu2B5O9X (X=Cl and Br) were determined by the method of X-ray diffraction analysis and refined by the least-square method to give R=0.054 for 1967 observed reflections of Eu2B5O9Cl and R=0.047 for 1979 observed reflections of Eu2B5O9Br. These haloborates are isostructural and belong to the orthorhombic (pseudotetragonal) system, with the Pnn2 space group and with four formula units in a cell of those dimensions: a=11.364(3), b=11.301(3), and c=6.504(2) A for Eu2B5O9Cl, and a=11.503(3), b=11.382(3), and c=6.484(2) A for Eu2B5O9Br. The structure consists of a three-dimensional (B5O9)∞ network, the B5O12 groups of three BO4 tetrahedra and two BO3 triangles being linked together with one another. The Eu and X atoms are located alternately in tunnels of the (B5O9)∞ network extending along the c axis. Each Eu atom is surrounded by two X atoms and seven O atoms, and is isolated from the neighboring Eu atoms attributable to borate units and X atoms. This arrangement of anions around Eu a...