scispace - formally typeset
Search or ask a question

Showing papers on "Orthorhombic crystal system published in 1982"


Journal ArticleDOI
TL;DR: The X-ray and neutron structures of polycrystalline Ca 2 MnO 3.5 by Rietveld analysis have been determined as mentioned in this paper, and the relationship between the CaMnO 3 /CaMnNO 2.5 structures is discussed.

317 citations


Journal ArticleDOI
TL;DR: In this paper, the precursors CaMnO 3 and Ca 2 MnO 4 were reduced with any one of a variety of inorganic (H 2, NH 3 ) or organic (C 2 H 4, C 3 H 6 ) reducing agents between 300 and 500°C.

196 citations



Journal ArticleDOI
TL;DR: It was found that when DPPC is incubated at 2 degrees C for three days the two-dimensional acyl chain packing changes from one resulting in spectra typical of an orthorhombic subcell to one resembling that found in triclinically packed acyl systems.

92 citations


Journal ArticleDOI
TL;DR: In situ X-ray diffraction measurements during stepwise hydrogenation of the intermetallic compound ZrNi confirmed the existence of a stable compound Z rNiH as mentioned in this paper, which is tetrahedrally coordinated by four zirconium atoms.
Abstract: In situ X-ray diffraction measurements during stepwise hydrogenation of the intermetallic compound ZrNi confirmed the existence of a stable compound ZrNiH. Neutron diffraction measurements on ZrNiD allowed a determination of the site occupied by deuterium. This site is tetrahedrally coordinated by four zirconium atoms as predicted earlier from a model based solely on geometric considerations. Occupation of this site causes the lattice to distort from an orthorhombic to a triclinic structure. The trihydride is formed when two completely different types of sites are filled, to the exclusion of the sites occupied originally, causing reversion of the lattice to an orthorhombic structure. Other confirmed predictions of the geometric model are discussed.

78 citations


Journal ArticleDOI
TL;DR: LiMgPO4 as mentioned in this paper is an ordered olivine-type polyhedra, where the inversion site is occupied by Li+ ions and the mirror site is taken by Mg2+ ions.
Abstract: LiMgPO4 is orthorhombic, space groupPnma,a=10.147(2),b=5.909(2),c=4.692(2)×10−10 m,D m =3000(8),D x =2980 kg m−3,Z=4,R=4.8% for 1262 observed reflections. The structure contains tetrahedral PO4 and octahedral LiO6 and MgO6 groups. It belongs to the ordered olivine-type structures, since the inversion site is occupied by Li+ ions and the mirror site is taken by Mg2+ ions. The distortion of polyhedra is caused mainly by the adjustment stresses between the different polyhedral dimensions and by the sharing of edges. Octahedral LiO6 share six and MgO6 share three common edges. The sharing of the O-O edges contributes to the stability of the bridging arrangements . The corresponding average distances of the O-O bridges are 2.432, 2.479, 2.883, and 3.028×10−10 m, while the average O-O distances in the PO4, MgO6, and LiO4 polyhedra are 2.512,2.921, and 3.015 × 10−10 m, close to the ideal values 2.531, 2.970, and 3.026×10−10 m respectively. The structure field of the olivine-type compounds plotted as a function of ionic radii in radius space is specified in relation to theβ-K2SO4, spinel, and K4NiF4 type structures. From the overlap of the structure fields, the high-pressure transformations of the olivine compounds are considered.

53 citations


Journal ArticleDOI
TL;DR: In this paper, solid solutions of the formula La2−xLnxCuO4 (Ln = Pr, Nd) possess the orthorhombic structure of La2NiO4 for small values of x and transform to the tetragonal Nd2NiF4 structure at a critical value of x.

53 citations


Journal ArticleDOI
TL;DR: In this paper, a transmission electron microscopy study has been made of the different martensites that form in Ti50Ni50 − xCux shape memory alloys in the composition range x = 1 to 19.

51 citations


Journal ArticleDOI
01 Dec 1982
TL;DR: The crystal structure of liebigite from X-ray 4-circle diffractometer data and refined toR=0.030 for 3005 observed reflections was found to crystallize in the polar orthorhombic space group with a cell content of 8 Ca2UO2(CO3)3·∼11H2O as mentioned in this paper.
Abstract: The crystal structure of liebigite, previously only incompletely known from a short note, has been determined from X-ray 4-circle diffractometer data and refined toR=0.030 for 3005 observed reflections. Liebigite from Joachimsthal, Bohmen, was used. It was found to crystallize in the polar orthorhombic space groupBba2−C 2 17 witha=16.699(3),b=17.557(3),c=13.697(3) A,V=4016 A3 and a cell content of 8 Ca2UO2(CO3)3·∼11H2O. The structure contains UO2(CO3)3 units which are linked by two kinds of CaO4(H2O)4 polyhedra and one kind of CaO3(H2O)4 polyhedron to form puckered Ca2UO2(CO3)3·8H2O layers parallel to (010). These layers are interconnected only by hydrogen bonds, both directly as well as via three additional interlayer H2O molecules, two of which show positional disorder.

51 citations


Journal ArticleDOI
TL;DR: In this article, the crystal data for α-, β-and γ-Ag2WO4 were collected from Cu Kα1 powder diagrams, α-Ag 2 WO4 is orthorhombic (Pn2n) with a = 10.820(2), b = 12.018(2) and c = 5.900(1)
Abstract: Crystal data for α-, β- and γ-Ag2WO4 were collected from Cu Kα1 powder diagrams, α-Ag2WO4 is orthorhombic (Pn2n) with a = 10.820(2), b = 12.018(2) and c = 5.900(1) A. β-Ag2WO4 is hexagonal (P63 or P63/m) with a = 11.0925(3) and c = 7.5424(4) A. γ-Ag2WO4 is cubic (Fd3m, spinel type) with a = 9.352(1) A.

50 citations


Journal ArticleDOI
TL;DR: In this article, Raman spectroscopy, X-ray diffraction analysis, differential scanning calorimetry and features of the preparative method are all consistent with the existence of 2 intermediate β' phases for tristearin; the first, a lower melting phase, β’2, transforms at 61 C into the second, β'1, which in turn changes at 64 C into β-tristearin.
Abstract: Data from Raman spectroscopy, X-ray diffraction analysis, differential scanning calorimetry and features of the preparative method are all consistent with the existence of 2 intermediate β’ phases for tristearin; the first, a lower melting phase, β’2, transforms at 61 C into the second, β’1 , which in turn changes at 64 C into β-tristearin. Raman spectral evidence indicates that the 2 mesophases occur in an orthorhombic packing environment and that the β’2 to β’1 transition results from a change in lateral packing of the hydrocarbon chains.

Journal ArticleDOI
TL;DR: The cytochrome P-450CAM monooxygenase from Pseudomonas putida has been crystallized in three forms designated orthorhombic I, tetragonal I, and orthorHombic II.


Journal ArticleDOI
TL;DR: In this article, Mao et al. reexamined their powder diffraction data for the distorted hcp structure and found the data can be satisfactorily interpreted in terms of the well-known orthorhombic α-uranium type of structure.
Abstract: H. K. Mao, R. M. Hazen, P. M. Bell, and J. Wittig [J. Appl. Phys. 52, 4572 (1981)] reported that praseodymium metal undergoes a crystallographic phase transformation from a distorted fcc structure to a distorted hcp structure at a pressure of ∼21 GPa. This phase change, further, is accompanied by a large volume decrease ∼19%. We have reexamined their powder diffraction data for the distorted hcp structure and find the data can be satisfactorily interpreted in terms of the well‐known orthorhombic α‐uranium type of structure. The volume decrease at the phase change is now estimated to be only ∼9.8%.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the high concentration phase has a disordered fluorite structure with a 0 = 4.27 A and its hydrogen content corresponds to TiCr1.8H5.3.
Abstract: An orthorhombic structure was originally assigned to the non-stoichiometric hydride TiCr1.8H3.6. Recent neutron and X-ray diffraction data indicated, however, that an alternative interpretation was possible, i.e. the solid consists of two hydride phases, an α′ Laves phase having a composition TiCr1.8H2.8 and an f.c.c. phase with a much higher hydrogen content. This proved to be the case and it was determined that the high concentration phase has a disordered fluorite structure with a 0 = 4.27 A . Its hydrogen content, as estimated from diffraction peak intensities, corresponds to TiCr1.8H5.3. We were not able to produce single-phase f.c.c. material but we prepared a mixed phase sample with an overall composition of TiCr1.8H4.8. The high pressure reaction leading to the formation of the fluorite phase is very sluggish and irreversible. Pressure-composition-temperature properties of this system were determined and are discussed and a revised phase diagram is proposed.

Journal ArticleDOI
TL;DR: The structure of a K x P 2 W 4 O 16 (x ⋍ 0.4) crystal was established by X-ray analysis as discussed by the authors, which can be described as two octahedra-wide ReO3-type slabs connected through “planes” of PO4 tetrahedra.

Journal ArticleDOI
TL;DR: In this article, the crystal and molecular structures of the title compounds have been determined from diffractometer data by the heavy-atom method, and the primary geometry about Te in (1) is based on a trigonal bipyramid with a vacant equatorial position, whereas (2) exhibits square-based pyramidal geometry for its two independent Te atoms, to give a chain structure.
Abstract: The crystal and molecular structures of the title compounds have been determined from diffractometer data by the heavy-atom method. The crystals of diphenyltellurium dichloride (1) are orthorhombic, space group Pbca, with unit-cell dimensions (173 K)a= 7.644(2), b= 18.160(3), c= 18.014(3)A, Z= 8, from 1 552 observed reflections [I/σ(I) 3.0], R= 0.036. Crystals of phenyltellurium trichloride (2) are triclinic, space group P, with unit-cell dimensions (290 K)a= 7.468(1), b= 8.610(1), c= 13.987(2)A, α= 98.89(1), β= 92.10(1), γ= 90.81 (1)°, Z= 4, from 2 903 observed reflections, R= 0.018. The primary geometry about Te in (1) is based on a trigonal bipyramid with a vacant equatorial position, whereas (2) exhibits square-based pyramidal geometry for its two independent Te atoms; these are bridged by Cl atoms, to give a chain structure. Both structures exhibit longer Te ⋯ Cl interactions, though these are weak and perhaps of little significance in (2).

Journal ArticleDOI
TL;DR: A method for computing the Lorentz tensor components in single crystals via rapidly convergent sums of Bessels functions is developed using the relationship between dipole-field sums and the tensor component as mentioned in this paper.
Abstract: A method for computing the Lorentz tensor components in single crystals via rapidly convergent sums of Bessels functions is developed using the relationship between dipole-field sums and the tensor components. The Lorentz factors for simple, body-centered, and base-centered orthorhombic lattices are computed using this method, and the derivative Lorentz factors for simple orthorhombic lattices are also determined. Both the Lorentz factors and their derivatives are shown to be very sensitive to a lattice structure. The equivalent of the Clausius-Mossotti relation for general orthorhombic lattices is derived using the Lorentz-factor formalism, and the permanent molecular dipole moment is related to crystal polarization for the case of a ferroelectric of polarizable point dipoles. It is concluded that the polarization enhancement due to self-polarization familiar from classical theory may actually be a reduction in consequences of negative Lorentz factors in one or two lattice directions for noncubic crystals.

Journal ArticleDOI
TL;DR: In this paper, structural work on the three modifications of sodium hydroxide is reviewed, and the phase-transition temperatures were determined by specific-heat measurements, respectively, using neutron and X-ray diffraction.
Abstract: Structural work on the three modifications of sodium hydroxide is reviewed. The monoclinic and cubic modifications were determined with neutron and X-ray diffraction, respectively. The phase-transition temperatures were determined by specific-heat measurements. The cubic to monoclinic transition is a first-order transition with a freezing of the rotational motion of the OH (and OD) groups. The monoclinic axes a, b and c* tend to be oriented parallel to the original cubic directions [{\bar 1}{\bar 1}2], [1{\bar 1}0] and [ 111], respectively. The orthorhombic to monoclinic transition is a nearly continuous displacive phase transition with a soft acoustic shear mode. The order parameter is the homogeneous shear of the crystal in the a direction. Its temperature dependence is described within Landau theory.

Journal ArticleDOI
L.H. Brixner1, H.-Y. Chen1, C.M. Foris1
TL;DR: LaWO 4 Cl as mentioned in this paper is representative of a series of Ln WO 4Cl compounds in which Ln can be La to Sm, Tb, and Eu, and their excitation and emission spectra are reported.

Journal ArticleDOI
TL;DR: Heptyl 1-thio-α-d -mannopyranoside, C 13 H 26 O 5 S, was solved by the direct method, and refined by full-matrix least-squares, to give agreement factors R = 0.030, R w =0.033, S = 1.61 as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, an extensive analysis of the intermolecular forces in the chlorine crystal has been performed, including anisotropic terms and electrostatic contributions from multipoles higher than quadrupole.
Abstract: An extensive analysis of the intermolecular forces in the chlorine crystal has been performed Different models of the intermolecular potential, including anisotropic terms and electrostatic contributions from multipoles higher than quadrupole have been taken into account and tested for their ability to reproduce static and dynamical properties of solid chlorine The inclusion of anisotropic dispersion forces reproduces correctly the orthorhombic unit cell Anisotropic terms are required also in the short range repulsive atom-atom interactions to obtain a good fit to lattice frequencies and stability of the Cmca structure with respect to a hypothetical cubic phase A tensor formalism, particularly convenient for dynamical calculations, is developed and used to describe angular dependent atom-atom interactions

Journal ArticleDOI
TL;DR: The structure of sulfamerazine, C11H12N4O2S, has been solved by direct methods with X-ray diffraction data collected using CuKα radiation.
Abstract: The structure of sulfamerazine, C11H12N4O2S, a very important sulfonamide drug, has been solved by direct methods with X-ray diffraction data collected using CuKα radiation. The crystals are orthorhombic, witha=9.145(1),b=11.704(1),c=22.884(2) A and space groupPbca. The structure was refined with 2082 observed independent reflections, measured on a CAD-4 diffractometer, to a finalR value of 0.078. The molecule has similar conformational features to those observed in other sulfonamide drugs.

Journal ArticleDOI
TL;DR: In this article, the vibrational dynamics as well as molecular and crystal structures were analyzed in terms of a model including a binuclear system with a double oxygen bridge, and the distribution of vibrational levels were carried out on the basis of optical and acoustic unit-cell mode analysis.

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of the orthorhombic copper salt Cu2(OH)3NO3 (natural gerhardtite) has been determined from X-ray diffractometer data by means of three-dimensional Patterson and Fourier syntheses, and refined by difference Fourier synthesis and least-squares methods to a finalR index of 0.097 for 532 reflections.
Abstract: The crystal structure of the orthorhombic copper salt Cu2(OH)3NO3 (natural gerhardtite) has been determined from X-ray diffractometer data by means of three-dimensional Patterson and Fourier syntheses, and refined by difference Fourier syntheses and least-squares methods to a finalR index of 0.097 for 532 reflections. Crystals of Cu2(OH)3NO3 are orthorhombic:a=6.087(2),b=13.813(4),c=5.597(2) A,Z=4, space groupP212121. The Cu atoms form deformed hexagonal pseudocells (010). Each Cu(1) ion is surrounded by an approximately square planar arrangement of four OH ions at 1.929, 1.952, 1.993 and 1.998 A and by two O (of NO3 ions) at 2.359 and 2.480 A, completing a deformed coordination octahedron; each Cu(2) ion is similarly coordinated by four OH at 1.989, 1.997, 2.009 and 2.018 A, one OH at 2.309 A, and one O at 2.384 A. The structure involves layers of such deformed octahedra, of theC6-type, linked together by hydrogen bonds through the NO3 ions. Similarities to and differences from the structure of the monoclinic polymorphous form are discussed.

Journal ArticleDOI
TL;DR: In this article, the structure of [Hg(4-MP)2]2+ cations and ClO4− anions packed in layers paralell to the (100) plane was determined by X-ray crystallography.

Journal ArticleDOI
TL;DR: The solid-state structures of the compounds (1)(Se42+)(Sb2F42+), (2)(Te42+)-SbF6−)2, and (3) Se42+(AlCl4-)2 are reported in this paper.
Abstract: The solid-state structures of the compounds (1)(Se42+)(Sb2F42+)(Sb2F5+)(SbF6–)5, (2)(Te42+)(SbF6–)2, and (3)(Se42+)(AlCl4–)2 are reported. The first compound was initially isolated from the reaction of a 1:3 sulphurselenium alloy with a SbF5–SO2 solution and the second by the reaction of a mixture of tellurium and germanium, with a SbF5–SO2 solution. They have also been prepared by the direct oxidation of Se and Te with SbF5 in SO2. Crystals of (1) are monoclinic, space group P21/c, with a= 15.739(3), b= 13.498(2), c= 17.040(4)A, β= 92.26(2)°, and Z= 4. The dark red plates of (2) are triclinic, space group A, with a= 5.700(2), b= 16.252(6). c= 8.076(2)A, α= 100.56(3), β= 102.67(3), γ= 97.47(3)°, and Z= 2. Compound (3) is orthorhombic, space group Pbam, with a= 13.245(3), b= 13.223(3), c= 9.266(2)A, and Z= 4. The structures of compounds (1) and (2) have been solved by direct methods and compound (3) by a Patterson function. They were refined by least squares to final agreement indices of R= 0.052 (R′= 0.062). 0.051 (0.064), and 0.042 (0.046) for 3 634, 709, and 912 observed reflections respectively. In these three compounds, the approximately square-planar chalcogen cations Se42+ and Te42+ were found to have crystallographic inversion symmetry with average Se–Se and Te–Te distances of 2.260(4)(1), 2.688(3)(2), and 2.286(2)A(3). These values are close to the distances observed in the other examples of these cations. The packing of these and other examples of the Ma42+ cations, the anion–cation charge-transfer interactions, and the stereochemistry of the fluorine contacts to the antimony(III) atoms in the Sb2F42+ and Sb2F5+ ions and related species are discussed.

Journal ArticleDOI
01 Jul 1982-Zeolites
TL;DR: The structure of nepheline hydrate I, Na3Al3Si3O12·2H2O, synthesized hydrothermally at 473 K, has been determined as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the X-ray structure of the title compound was determined by Xray analysis and the structure was solved by the heavy-atom method and refined by least-squares calculations to a final R value of 0.034.
Abstract: The crystal structure of the title compound was determined by X-ray analysis. The compound crystallizes in the orthorhombic space group P212121 with cell dimensions a= 12.306(2), b= 8.996(2), c= 7.596(1)A, and Z= 4. The structure was solved by the heavy-atom method and refined by least-squares calculations to a final R value of 0.034. The compound is isostructural with the corresponding zinc(II) salt. The structure consists of polymeric linear chains in which the Ni atom is co-ordinated in a distorted octahedral manner by one aspartate ion, acting as a tridentate ligand, by two water molecules, and by one β-carboxylate O atom of a second aspartate ion. Magnetic and spectroscopic results are also discussed.

Journal ArticleDOI
TL;DR: In this article, the perovskite structure of KmnCl 3 is shown to be orthorhombic and the space group is Pnma and Z = 4.