Showing papers on "Orthorhombic crystal system published in 1976"
TL;DR: In this article, a theory was developed on the free vibration of a crystal of rectangular parallelepiped and of general symmetry by extending Demarest's theory of cube resonance, which is applied to determine elastic constants of crystals from the resonance frequencies of its free vibrations.
Abstract: A theory was developed on the free vibration of a crystal of rectangular parallelepiped and of general symmetry by extending Demarest's theory of cube resonance. All vibrational modes were classified and described in detail for the case of orthorhombic symmetry. The theory is applied to determine elastic constants of crystals from the resonance frequencies of its free vibrations. The method of numerical analysis of resonance frequency data was studied to derive a practical way of elastic constant determination. As an example, the elastic constants of two specimens of single crystal olivine (Mg1.8Fe0.2SiO4) were determined. The applicability of the resonance method is largely extended by the present theory to the precise determination of elastic constants of single crystals.
395 citations
TL;DR: In this paper, the authors used X-ray diffraction, neutron diffraction and magnetometric methods to obtain a model of the spiral magnetic structure of NiMnGe and found that at temperature Tt = 185 K the spiral axis is in the bc-plane.
Abstract: NiMnGe is investigated by means of X-ray diffraction, neutron diffraction, and magnetometric methods. The orthorhombic distorsion of hexagonal lattice is observed below 470 K. The compound NiMnGe is antiferromagnetic with a Neel temperature TN = 346 K. The jump observed at temperature Tt = 185 K on the temperature dependence of magnetic susceptibility points at the change of a magnetic structure. From the analysis of the neutron diffraction patterns the following models of spiral magnetic structure are obtained; at T < Tt the spiral axis is in the bc-plane. The angle between the spiral axis and the b-axis is 45°, magnetic moment at 80 K is 2.75μB; at Tt < T < TN the spiral axis is along the a-axis. The magnetic moment at 295 K is 2.2μB.
153 citations
TL;DR: In this article, a trigonal pyramid was constructed for the selenites and tellurites, where the structure was described as a distorted perovskite or a salt of M2+ and SeO32− or TeO 32− ions.
118 citations
112 citations
TL;DR: In this paper, the kinetics of transformation behavior of roller-quenched amorphous Pd 83 Si 17 and Pd 80 Si 20 alloys after linear and isothermal heating was reported.
Abstract: The kinetics of transformation behavior of roller-quenched amorphous Pd 83 Si 17 and Pd 80 Si 20 alloys after linear and isothermal heating is reported. The transformation was examined with electron microscopy, electron diffraction and electrical resistivity measurement. The crystallization of amorphous alloys with 17 at% Si begins with metastable ordered fcc solid solution. The ordered fcc solution is transformed to a ordered metastable phase with, probably, orthorhombic structure. The crystallization of amorphous alloys with 20 at% Si begins by formation of spherulites with lamellar structure. Using electron diffraction we found that spherulites consist of two phases - orthorhombic Pd 3 Si silicide and Pd-rich silicide. From resistivity measurements, activation energies of 28.5 kcal/mol for Pd 83 Si 17 and 80 kcal/mol for Pd 80 Si 20 , respectively, were calculated.
104 citations
TL;DR: In this article, the Δ E effect due to the displacement of antiferromagnetic domain walls was investigated for polycrystalline γ Mn-Ni alloys with a temperature range between −180° and 250°C.
Abstract: Lattice parameters and elastic moduli of polycrystalline γ Mn alloys containing 12–40 at% Ni have been measured in a temperature range between –180° and 250°C. The face-centred cubic lattice undergoes a tetragonal distortion, either c / a 1, or an orthorhombic distortion at low temperatures. Both Young's modulus and shear modulus exhibit a step-type change at the Neel point and a broad minimum near the transition temperature of lattice distortion. The elastic behaviour is discussed on the basis of the so-called Δ E effect due to the displacement of antiferromagnetic domain walls. This effect may possibly be enhanced by the lattice softening in the γ Mn–Ni alloys.
102 citations
TL;DR: In this article, Epstein and Bernal showed that the Ballhausen-Dahl model is not valid for M(h5−C5H5)2L2 systems.
90 citations
TL;DR: The crystal structure of the copper(I) iodide pyridine adduct has been determined by X-ray diffraction at 295 K and refined by least squares to R 0.057 for 2 710 "observed" reflections as mentioned in this paper.
Abstract: The crystal structure of the copper(I) iodide pyridine adduct has been determined by X-ray diffraction at 295 K and refined by least squares to R 0.057 for 2 710 ‘observed’ reflections. Crystals are orthorhombic, space group P212121, with a= 16.032(6), b= 15.510(2), and c= 11.756(3)A. The asymmetric unit is Cu4I4py4, based on the well-known tetrahedral tetrameric Cu4I4 unit, with Cu–N 2.04, Cu–I 2.70, and Cu–Cu 2.69 A; the latter distance is much shorter than in the analogous complexes formed with phosphine and arsine ligands.
90 citations
TL;DR: In this paper, the structure of the title compound was determined from 2 807 observed X-ray intensities, measured by diffractometer, and the phase problem was solved by Patterson rotation and translation methods.
Abstract: Crystals of the title compound are monoclinic, space group A2, with lattice parameters a= 10.260(8), b= 7.596(8), c= 101.43(9)A, β= 94.41(5), and Z= 8 [2 independent molecules (A) and (B)]. The structure was determined from 2 807 observed X-ray intensities, measured by diffractometer. The phase problem was solved by Patterson rotation and translation methods. Refinement by block-diagonal least-squares gave R 0.079. Molecules (A) and (B) have almost fully extended conformations, but differ significantly in the rotation about the ester bond and in the C(17) chains. The crystal structure consists of stacked bilayers 50·7 A thick. The C(17) chain ends, which lie at the bilayer surfaces, are virtually liquid. Within a bilayer cholesterols pack with cholesterols, and myristate chains pack with myristate chains. The chain packing has an orthorhombic (Oa) subcell. The inner diffraction ring at sin θ/λ 0.015 A–1, 0.016 A–1 which has been observed for the smectic A and cholesteric mesophases respectively, may be a result of multiple almost parallel 33 A vectors which exist between atoms of cholesterols on opposite sides of a bilayer. Thus, we infer that the mesophases retain some characteristics of the crystal structure.
76 citations
TL;DR: In this article, the spinels of Co 2 GeO 4 and Ni 2 geO 4 have been found to disproportionate into their isochemical oxide mixtures at about 250 kbar and 1400-1800°C in the same manner as their silicate analogues.
73 citations
TL;DR: In this article, the anomalous spectrum of the orthorhombic KNb${\mathrm{O}}_{3}$ is found to contain anomalous scattering, consisting of a large background and broad bands, which can be related directly to the dynamic disorder which has been invoked to explain the results of earlier studies of diffuse x-ray scattering and inelastic neutron scattering.
Abstract: The Raman spectrum of orthorhombic KNb${\mathrm{O}}_{3}$ is found to contain anomalous scattering, consisting of a large background and broad bands, which can be related directly to the dynamic disorder which has been invoked to explain the results of earlier studies of diffuse x-ray scattering and inelastic neutron scattering. Some ordinary first-order lines exhibit coupling to the anomalous part of the spectrum, which is revealed by the existence of resonant interference of the type described by Fano. All these features disappear abruptly at the transition to the low-temperature rhombohedral phase, indicating that they are characteristic of the peculiar dynamics of linear chains observed in the orthorhombic, tetragonal, and cubic phases.
TL;DR: In this paper, the trace of the force-dipole tensor (A+2B) as well as the components A and B of hydrogen interstitials in niobium were determined from measurements of the lattice parameters of the alpha, alpha'and beta phases.
Abstract: The trace of the force-dipole tensor (A+2B) as well as the components A and B of hydrogen interstitials in niobium were determined from measurements of the lattice parameters of the alpha , alpha ' and beta phases. It is shown that the orthorhombic structure of the beta phase is due to a direct hydrogen-hydrogen interaction. A parameter H, analogous to A or B and representing the strength of this direct interaction, is deduced assuming a central force model. It is shown that the concentration dependence of the structural parameters is correctly predicted by this model. The values of A, B and H are 2.88, 2.75 and 0.05 eV or 2.88, 2.84 and -0.05 eV respectively depending upon whether the nearest-neighbour direct hydrogen-hydrogen interaction is repulsive or attractive.
TL;DR: The new, layered bismuth titanates, Bi7Ti4NbO21 and Bi6Ti3WO18, were synthesized by heating mixtures of the constituent oxides at 1100 °C in air, and were analyzed by X-ray powder diffraction as mentioned in this paper.
Abstract: The new, layered bismuth titanates, Bi7Ti4NbO21 and Bi6Ti3WO18, were synthesized by heating mixtures of the constituent oxides at 1100 °C in air, and were analyzed by X-ray powder diffraction. Bi7Ti4NbO21 has an orthorhombic cell with a = 5.44, b = 5.40 and c = 29.05 A, and it is thought that the structure is built up by regular intergrowth of Bi4Ti3O12 and Bi3TiNbO9 layers along the c-axis. Bi6Ti3WO18 has an orthorhombic cell with a = 5.38, b = 5.40 and c = 24.96 A, which is consistent with that of Bi3TiNbO9 reported by Wolfe et al., and with which it is thought to be iso-structural.
Journal Article•
TL;DR: The crystal structure of hopeite, Zns(POa)2.4Hro, has been solved by the Heavy Atom method from l42l graphite-monochromatized MoKa data and refined by full matrix least-squares to R = 0.026 (R. = 1.036).
Abstract: The crystal structure of hopeite, Zns(POa)2.4Hro, has been solved by the Heavy Atom method from l42l graphite-monochromatized MoKa data and refined by full matrix least- squares to R = 0.026 (R. = 0.036). The structure is orthorhombic, pnma, a = 10.597(3), b : l8.3lE(8), c: 5.031(l) A, and Z: 4.Thezn atoms occur in two crystallographically sites, one six-coordinated and deficient in zn, the other four-coordinated. The a and 0 modifications of this mineral are discussed in relation to its thermal dehvdration and infrared absorption properties.
TL;DR: The vapour spectrum of pyrrole was investigated below 39 000 cm-1 and four Rydberg-like series were observed with a vibrational pattern that appears to be similar to the one previously found for other simple heterocycles, and to involve excitations of v 8, v 7, v 5, v 4 as mentioned in this paper.
Abstract: The vapour spectrum of pyrrole was investigated below 39 000 cm-1. Four Rydberg-like series were observed with a vibrational pattern that appears to be similar to the one previously found for other simple heterocycles, and to involve excitations of v 8, v 7, v 5, v 4. The series lead to the lowest ionization potential (8·215 eV). No evidence was found of Rydberg series leading to the next ionization potential. The weak system near 46 000 cm-1 is tentatively assigned to a 1 B 1 ← [Xtilde]1 A 1 valence-shell transition, while the very weak absorption in the range 40 000–44 000 cm-1 may partly or wholly be due to a 3s excitation of mixed character. The crystal spectrum in polarized light was measured in the range 45 000–55 000 cm-1. It is slightly dichroic, and shows two diffuse absorption systems. Optical observations and spectral data indicate that the crystal structure of pyrrole is orthorhombic, probably with four molecules in the unit cell.
TL;DR: In this article, the relation between the crystal structures of Cu(NH3)2(NCS)2 and CuNCS is discussed. And the structure was refined by the method of full matrix least squares, yielding the value 0.062 for the R factor.
TL;DR: In this article, the opticmode spectrum of orthorhombic KNbO at room temperature was determined by using Raman scattering and infrared reflectivity measurements, and the spectral anisotropic properties of the optic modes were determined.
Abstract: Both Raman scattering and infrared reflectivity measurements have been performed to determine the opticmode spectrum of orthorhombic KNbO, at room temperature. Pincipal-axis phonons and oblique phonons were observed with a combination of 90 scattering, back scattering, and forward scattering. Unobserved longitudinal modes and mode couplings were derived from the reflectivity measurements. The ferroelectric modes, namely those rendered highly anisotropic as a result of successive transitions, were identified and their spatial anisotropy determined; strong interference with more isotropic modes was pronounced. Dielectric constants were derived from these measurements and the A, polariton dispersion curve was also measured. The modes were grouped according to the cubic representations from which they are derived and compared with those of BaTiO, : In particular the modes were three time less damped. Of the original soft cubic ferroelectric mode, the component along the remaining soft direction was found at 56 cm ' and not
TL;DR: In this article, the magnetic behavior of the (CnH2n+1NH3)2MnCl4-family has been studied and the room temperature phase of members with odd numbers of carbon atoms is orthorhombic whereas even numbers lead to monoclinic structures.
TL;DR: The crystal structure of (1,1′-ferrocenediyl)diphenylsilane has been determined from analysis of photographic X-ray data.
Abstract: The crystal structure of (1,1′-ferrocenediyl)diphenylsilane has been determined from analysis of photographic X-ray data. The crystal system is orthorhombic, a = 14.18(2), b = 12.54(2), c = 9.28(1) A, space group Pnma with four formula units. The molecule has crystallographic m (Cs) symmetry with atoms Fe and Si lying in the mirror plane, which bisects the two phenyl groups. The planar cyclopentadienyl rings are bridged by a single silicon atom, and are tilted 19.2° with respect to one another. The Fe—C(Cp) distances vary from 2.01(1) to 2.11(1) A. The bridging angle C(1)—Si—C(1′) is 99.1°, while the Si—C(sp2) bond lengths range from 1.86 to 1.88 A. The exocyclic C(1)—Si bond makes an angle of 40° with respect to the plane of the cyclopentadienyl ring.
TL;DR: In this paper, the crystal structure of the α-cyclodextrin-sodium benzenesulfonate complex was determined by X-ray analysis, which has a channel-type structure.
Abstract: The crystal structure of the α-cyclodextrin-sodium benzenesulfonate complex, which has a channel-type structure, was determined by X-ray analysis. The crystals were orthorhombic with the space group of P21212, cell dimensions of a=21.832(3), b=16.529(2), and c=8.356(1) A, and Z=2. The structure was determined on the basis of 2894 diffractometer data and refined by the block-diagonal least-squares methods to the final R-value of 0.069. The benzenesulfonate anion is arranged in the channel which is formed by the stack of α-cyclodextrin rings along the c axis. The benzene ring is located in the cavity, while the sulfonato group is hydrogen-bonded to the primary hydroxyl groups of the adjacent α-cyclodextrin molecule. The space outside the channel is filled with water molecules and sodium ions, and the hydrogen-bonding network is formed. The energy of the complex formation was calculated for two possible structures of the 1 : 1 complex in an aqueous solution.
TL;DR: In this article, a double-infusion technique was used to synthesize the cobalticyanides LnCoIII(CN)6·nH2O with Ln = La,…, Lu, Y. Experiments show that no magnetic ordering occurs down to 1°K.
TL;DR: In this article, a hexagonal version of the LuMnO3 structure was obtained at atmospheric pressure of 0.34 kbar, 1000°C, where the In3+ ions are located in fivefold-coordinated trigonal-bipyramidal sites, and the Ln3+ ion are sevenfold coordinated.
TL;DR: In this paper, the Madelung part of lattice energy (MAPLE) as well as the effective coordination numbers (ECoN) of BaZrF6 are calculated and discussed.
Abstract: Neu dargestellt wurden BaZrF6, PbZrF6, EuZrF6 und SrZrF6 (alle farblos); diese kristallisieren nach Einkristalldaten orthorhombisch D–Cmma; BaZrF6: a = 7,681, b = 11,357, c = 5,511 A; PbZrF6: a = 7,546, b = 11,118, c = 5,308 A; EuZrF6: a = 7,553, b = 10,945, c = 5,339 A; SrZrF6: a = 7,547, b = 10,889, c = 5,326 A.
Die Strukturbestimmung an BaZrF6 zeigt, das, ahnlich dem K2ZrF6 [3], [ZrF4/2F4/1]-Einer-einfachketten vorliegen, Zr4+ also von 8 F− umgeben ist (Abstande sowie Parameter vgl. Text).
Der Madelung-Anteil der Gitterenergie, MAPLE, sowie „Effektive Koordinationszahlen”, ECoN, werden berechnet und diskutiert.
New Hexafluorozirconates(IV): BaZrF6, PbZrF6, EuZrF6, SrZrF6
The new compounds BaZrF6, PbZrF6, EuZrF6 und SrZrF6 (all colourless) crystallize according to single crystal investigations orthorhombic. Data see „Inhaltsubersicht”.
From the determination of crystal structure of BaZrF6 results, that similar to K2ZrF6, there are [ZrF4/2F4/1]-chains. Zr4+ is therefore surrounded by eight fluorine atoms (distances and parameters see text).
The Madelung part of lattice energy (MAPLE) as well as the effective coordination numbers (ECoN) are calculated and discussed.
TL;DR: In this paper, the quadrupole coupling of 14N in the room temperature orthorhombic (Cmca), the low temperature tetragonal (P42/ncm), and the monoclinic low temperature (P21/c) phases of (CH3NH3)2CdCl4 was determined.
Abstract: Using a proton-nitrogen double resonance technique we have determined the quadrupole coupling of14N in the room temperature orthorhombic (Cmca), the low temperature tetragonal (P42/ncm), and the monoclinic low temperature (P21/c) phases of (CH3NH3)2CdCl4. In all these phases all nitrogens are chemically equivalent demonstrating that the disorder in the orientations and H-bonding arrangements of the CH3-NH3 groups in theC m c a andP42/ncm phases is indeed dynamic and not static. In the monoclinic phase the14N quadrupole coupling constant equalse2qQ/h=880 kHz and the asymmetry parameter isη=0.20, wherease2qQ/h=790 kHz,η=0.1 in the tetragonal low temperature phase ande2qQ/h=726 kHz,η=0.21 in the room temperature orthorhombic phase. The observed increase in the14N quadrupole coupling constant on going from the orthorhombic phase to the tetragonal low temperature phase which is coupled with a simultaneous decrease in the asymmetry parameter can be understood in terms of a partial freezing in of the dynamic disorder in the C-N bond directions whereas the14N quadrupole coupling tensor in the monoclinic phase is characteristic of a frozen in C-N bond in a deformed lattice, where the N-H — Cl bonds are of different length.
TL;DR: The crystal and molecularn structure of (π-cyclopentadienyl)(π-cyclobutadiene)- cobalt (C 5 H 5 )(C 4 H 4 ) has been determined by single crystal X-ray diffraction techniques using three-dimensional data gathered at ca.-35 C by counter methods as discussed by the authors.
TL;DR: In this article, the authors compared the geometrical variations which occur when a quadridentate Schiff-base co-ordinates to a cobalt(II) atom on the basis of the crystal structure analysis of the ligand NN′-(o-phenylene) bis(salicylideneamine) and its CoII derivative in its orthorhombic (II) and monoclinic (III) modifications.
Abstract: Geometrical variations which occur when a quadridentate Schiff-base co-ordinates to a cobalt(II) atom are compared on the basis of the crystal structure analysis of the ligand NN′-(o-phenylene) bis(salicylideneamine)(I) and its CoII derivative in its orthorhombic (II) and monoclinic (III) modifications. Crystals of (I) are monoclinic, space group P21/c, with cell parameters: a= 6.064(3), b= 16.541(7), c= 13.306(7)A, β= 91.5(1)°. Crystals of (II) are orthorhombic, space group P212121, with a= 16.755(7), b= 17.532(8), c= 5.362(3)A, and of (III) are monoclinic, space group P21/nwith a= 10.681(5), b= 8.354(4), c= 18.185(8)A, β= 105.3(1)°. A total of 1 277 (I). 1 113 (II), and 2 558 (III) independent reflexions were used : the structures were solved from diffractometer data by the heavy-atom method and refined to final R factors of 0.056 (I), 0.046 (II), and 0.041 (III). The enolimine form is established for (I) in the solid state. Upon co-ordination, with formation of (II) and (III), the geometrical data suggest that the contribution to the resonance of a ketamine form becomes as important as that of the enolimine. This is in agreementwith a π-orbital delocalization of the electronic charge over the planar complex molecule.
TL;DR: In this article, it was shown that positive definiteness of the strain energy is a sufficient condition for the existence of a unique pure surface mode in a semi-infinite elastic body with a traction-free boundary.
TL;DR: In this paper, the crystal and molecular structure of aquadichlorocaffeinecopper (II) was determined by three-dimensional X-ray data, and the structure was solved by the heavy-atom method from 1221 reflections collected by counter, and refined by least-squares method to R = 0.028.
TL;DR: In this article, a fast Fortran program written in Fortran is presented to calculate the unit-cell dimensions of triclinic and orthorhombic lattices.
Abstract: A fast computer program written in Fortran is presented. It calculates with a trial-and-error method the unit-cell dimensions from the d values obtained from powder patterns. The special techniques used in this program to keep the computation time short are described. The program itself is designed primarily for triclinic and orthorhombic lattices. Monoclinic lattices are treated like triclinic ones: for tetragonal, hexagonal and rhombohedral structures orthorhombic cells can be calculated.
TL;DR: The title compound of as mentioned in this paper is orthorhombic with a= 11.116(11), b= 12.043(9), c= 7.646(5)A, space group Pbca, Z= 8.029 for 1029 observed reflections.
Abstract: Crystals of the title compound are orthorhombic with a= 11.116(11), b= 12.043(9), c= 7.646(5)A, space group Pbca, Z= 8. The structure was solved from three-dimensional diffractometer data by Patterson and Fourier methods and refined by block-diagonal least-squares to R 0.029 for 1029 observed reflections. The structure consists of protonated cations in the cis-conformation, i.e. with the –NH–NH2 group bent towards the CS bond, and of chloride anions. Packing is determined by hydrogen-bonds formed by the –NH2+, –NH2, and NH groups with Cl- and S.