Delindeite titanosilicates and lourenswalsite, two new from the Magnet Cove region, Arkansas

1987 ◽  
Vol 51 (361) ◽  
pp. 417-425 ◽  
Author(s):  
Daniel E. Appleman ◽  
Howard T. Evans ◽  
Gordon L. Nord ◽  
Edward J. Dwornik ◽  
Charles Milton
Keyword(s):  
Electron Diffraction ◽  
Molar Volume ◽  
Hot Spring ◽  
Unit Cell ◽  
Volume Data ◽  
X Ray ◽  
Ion Probe ◽  
Layer Disorder ◽  
Miarolitic Cavities ◽  
Measured Density

AbstractDelindeite and lourenswalsite are two new barium titanosilicate minerals found as microscopic crystals in miarolitic cavities in nepheline syenite in the Diamond Jo quarry, Hot Spring County, Arkansas. Delindeite is found as aggregates of flake-like crystallites in compact spherules, light pinkish grey in colour, with a resinous, pearly lustre. The flakes are biaxial positive with average n ∼ 1.813; the measured density is 3.3 g/cm3. Electron diffraction revealed a monoclinic unit cell in space group C2/m or subgroup, with a = 21.617(13), b = 6.816(5), c = 5.383(3) Å, β = 94.03(5)° (refined from X-ray powder data). The strongest X-ray lines are (hkl, dobs, Irel): (200, 10.80, 100); (311, 3.54, 24); (6̄01, 3.083, 28); (601, 2.888, 31); (2̄21, 2.806, 20); (910, 2.262,18). The crystals are submicroscopically twinned on (100) and also produce additional continuous diffraction streaks parallel to a*, which double the b and c axes. The formula derived from electron and ion probe analyses (H2O by difference), as constrained by density and molar volume data, is approximately (Na,K)2.7(Ba,Ca)4(Ti,Fe,Al)6Si8O26(OH)14, with Na > K, Ba ≫ Ca, Ti ≫ Fe,Al; Z = 1. Lourenswalsite occurs as very thin hexagonal plates in rosettes, silver grey to light brownish grey in colour. The crystals are biaxial negative with very low 2V angle. Indices of refraction are nα = 1.815, nβ ≈ nγ = 1.840; the measured density is 3.17 g/cm = 1.840; the measured density is 3.17 g/cm3. X-ray and electron diffraction show a sharp pseudohexagonal lattice with a = 5.244 Å, but extremely diffuse diffraction streaks normal to the hk0 plane. In these streaks a period of 20.5 Å can be discerned. A hexagonal unit cell with a = 5.244(2) Å, c = 20.49(3) Å can be refined from the powder diffraction data but does not account for some lines, probably because of extreme layer disorder as shown by precession single-crystal patterns. The strong X-ray powder lines are (002, 10.22, 20); (-, 3.93, 20); (111, 2.608, 100); (300, 1.5145, 80); (220, 1.3111, 25). The formula given by microprobe analyses, constrained by density and molar volume data, is approximately (K,Ba)2(Ti,Mg,Ca,Fe)4(Si,Al,Fe)6O14(OH)12 with K > Ba, Ti ≫ (Mg,Ca,Fe), Si > Al > Fe; Z = 1. These minerals are formed under oxidizing weathering conditions, and iron is assumed to be in the Fe3+ state.

New Applications of Electron Diffraction in the Pharmaceutical Industry: Polymorph Determination by Using a Combination of Electron Diffraction and Synchrotron X-ray Powder Diffraction Techniques

2002 ◽  
Vol 8 (2) ◽  
pp. 134-138 ◽  
Author(s):  
Z.G. Li ◽  
R.L. Harlow ◽  
C.M. Foris ◽  
H. Li ◽  
P. Ma ◽  
...  
Keyword(s):  
Pharmaceutical Industry ◽  
Electron Diffraction ◽  
Powder Diffraction ◽  
Unit Cell ◽  
X Ray ◽  
Cell Parameters ◽  
Synchrotron Powder Diffraction ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
New Applications

Electron diffraction has been recently used in the pharmaceutical industry to study the polymorphism in crystalline drug substances. While conventional X-ray diffraction patterns could not be used to determine the cell parameters of two forms of the microcrystalline GP IIb/IIIa receptor antagonist roxifiban, a combination of electron single-crystal and synchrotron powder diffraction techniques were able to clearly distinguish the two polymorphs. The unit-cell parameters of the two polymorphs were ultimately determined using new software routines designed to take advantage of each technique's unique capabilities. The combined use of transmission electron microscopy (TEM) and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large-unit-cell, micron-sized) polymorphic pharmaceutical compounds.

Using Electron Diffraction Technique to Solve Real World Problems

2001 ◽  
Vol 7 (S2) ◽  
pp. 554-555
Author(s):  
Z. G. Li
Keyword(s):  
Electron Diffraction ◽  
Real World ◽  
Unit Cell ◽  
X Ray ◽  
Cell Parameters ◽  
Research Division ◽  
Commercial Scale ◽  
Electron Diffraction Technique ◽  
Superconducting Compounds ◽  
Real World Problems

Electron diffraction can be a very useful technique in solving real world structure-related problems. However, electron diffraction is much less widely used in industry compared to x-ray diffraction for several reasons. So far, application of electron diffraction has been limited to large-sized companies either to characterize newly synthesized materials in a research division or to directly support business activities in an analytical laboratory. New materials produced on a commercial scale are more and more complex with micro-, even nano-meter sized structures. Development of these materials on a commercial scale, for example, high temperature superconducting compounds, fullerenes, and giant magneoresistance devices [1-7], has increased demand for electron diffraction techniques considerably. Here, I would like to review how electron microscopists in industry solve their real world problems using electron diffraction techniques [8].Unit cell determination. Unit cell parameters and atom coordinates of a crystal can be routinely determined by single crystal x-ray technique if the crystal is large enough (about 0.1 mm in size).

The fibrous zeolite erionite; its occurrence, unit cell, and structure

1959 ◽  
Vol 32 (247) ◽  
pp. 261-281 ◽  
Author(s):  
Lloyd W. Staples ◽  
J. A. Gard
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Unit Cell ◽  
Original Material ◽  
Space Group ◽  
X Ray ◽  
Rotation Pattern ◽  
Structure Factors ◽  
Atomic Cell ◽  
Fibre Rotation

SummaryThe type locality for erionite has been identified and specimens compared with Eakle's original material. New determinations of the physical properties and a chemical analysis have been made. Correlation of X-ray powder and fibre rotation data with electron diffraction of single crystals has shown that the unit cell is hexagonal with a 13·26, c 15·12 Å., space-group P31c, P¯31c, P63mc, P¯62c, or P63/mmc, giving a calculated sp. Gr. of 2·07 and atomic cell contents (Ca, Mg, Na2, K2)4·5Al9Si27O72.27H2O. A structure is proposed for the aluminosilicate frame, with space-group P63/mmc, which gives satisfactory correlation between observed and calculated structure factors for the X-ray fibre rotation pattern.

Crystal structure of a new compound Li2Mg2(WO4)3

1994 ◽  
Vol 9 (3) ◽  
pp. 158-160 ◽  
Author(s):  
Zhengmin Fu ◽  
Wenxiu Li
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Unit Cell ◽  
Lattice Parameters ◽  
Orthorhombic System ◽  
Space Group ◽  
X Ray ◽  
Measured Density

The crystal structure of a new compound Li2Mg2(WO4)3 has been determined by means of X-ray powder diffraction. Li2Mg2(WO4)3 belongs to the orthorhombic system, with space group Pnma and the lattice parameters are: a = 5.1129 Å, b = 10.462 A, and c = 17.612 Å at room.temperature. Its measured density is Dm = 5.48 g/cm3, and each unit cell contains four formula weights.

Preparation and Partial Characterization of Two New Hexavalent Uranium Metal Uranates

1996 ◽  
Vol 49 (7) ◽  
pp. 817 ◽  
Author(s):  
M Sterns ◽  
RL Withers ◽  
P Midgeley ◽  
R Vincent
Keyword(s):  
Electron Diffraction ◽  
Structural Investigation ◽  
Chemical Characterization ◽  
Unit Cell ◽  
Tetragonal Symmetry ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Cell Dimensions ◽  
Unit Cell Dimensions

The preparation, chemical characterization and structural investigation by X-ray and electron diffraction of two uranates (VI), namely Sr5U3O14 and of Pb11U5O26, are reported. The strontium compound, the unit cell of which is metrically tetragonal with a = 11.248(5), c = 11.086(5) Ǻ, Z = 4, was shown by electron diffraction to be orthorhombic, space group Pbca with a = b. Crystals of Sr5U3O14 are invariably submicroscopically twinned and, because of the identity of a and b, mimic tetragonal symmetry. The lead uranate , Pb11U5O26, was shown to be a long-period superstructure with unit cell dimensions a = 44.54, b = 15.586, c = 8.241 Ǻ, Z = 8.

Superstructures and defects in alloys with the γ-brass structure

1978 ◽  
Vol 36 (1) ◽  
pp. 342-343
Author(s):  
A.J. Morton
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Transition Metals ◽  
Unit Cell ◽  
Defects In Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Prototype Structure ◽  
Alloy Systems

In a very wide range of alloy systems, but particularly those of the noble and transition metals with zinc and cadmium, alloys are formed with the so-called 'γ-brass crystal structure' or structures closely related to it. The prototype structure has a body-centred cubic unit cell containing 52 atoms and is non-centrosymmetric. Recognised variants of the structure include both a primitive cubic cell of 52 atoms and a face-centred cell of 416 atoms and there is also a rhombohedral cell which is only very slightly distorted from cubic. However in some systems such as the Cu-Zn, Ni-Zn and Pd-Zn systems unidentified “non-cubic” superstructures have been proposed from x-ray diffraction studies. In this study TEM and electron diffraction have been used to determine the nature of these superstructures and to identify defects in crystals with the γ-brass structure.Figures 1 and 2 show that two distinct superstructures form in Cu-rich γ-brass.

scholarly journals An X-ray analysis of the structure of chrysene

1934 ◽  
Vol 146 (856) ◽  
pp. 140-153 ◽  
Keyword(s):  
Room Temperature ◽  
Unit Cell ◽  
Molecular Volume ◽  
Crystal Data ◽  
Monoclinic System ◽  
Space Group ◽  
X Ray ◽  
Space Groups ◽  
Measured Density

Chrysene crystallizes in the monoclinic system. By means of rotation, oscillation, and moving film photographs the following crystal data have been obtained:— a = 8·34 A, b = 6·18 A, c = 25·0 A, β = 115·8°. All the planes ( hkl ) are halved when h + k + l is odd and in addition all the ( h 0 l ) planes are halved. There are two space groups available, C 6 2 h (I2/ c ) and C 4 s (I c ). In what follows it will be shown that the former space group is the more probable. The measured density is 1·27 (at room temperature) giving 4 molecules of C 18 H 12 per unit cell. Molecular volume = 290 (A) 3 .

β-Ferric Oxyhydroxide

1960 ◽  
Vol 32 (250) ◽  
pp. 545-557 ◽  
Author(s):  
A. L. Mackay
Keyword(s):  
Iron Oxide ◽  
Electron Diffraction ◽  
Spinel Phase ◽  
Intermediate Stage ◽  
Unit Cell ◽  
X Ray ◽  
Hydrated Iron Oxide ◽  
Tetragonal Unit Cell ◽  
Ferric Oxyhydroxide ◽  
Hydrolysis Of

SummaryThe crystallographic properties of the hydrated iron oxide obtained by the hydrolysis of FeCl3 are described. The characterizing X-ray powder pattern can be indexed on a tetragonal unit cell with a 10·48 and c 3·023 Å. This cell is shown to contain eight formula units of FeOOH but Cl- or other anions are necessary for the crystallization of the material The structure is that of hollandite or α-MnO2. The unit cell has been confirmed by electron diffraction from single crystals having dimensions about 5000 × 500 × 500 Å. and twinning, which produces hexagonal stars, has been studied. On heating, the structure breaks down and recrystallizes as α-Fe2O2, probably with an intermediate stage involving a spinel phase.

Okenite and nekoite (a new mineral) (With Plate I.)

1956 ◽  
Vol 31 (232) ◽  
pp. 5-21 ◽  
Author(s):  
J. A. Gard ◽  
H. F. W. Taylor
Keyword(s):  
Optical Properties ◽  
Electron Microscope ◽  
New Species ◽  
Electron Diffraction ◽  
Unit Cell ◽  
New Mineral ◽  
X Ray ◽  
A New Species

SummaryThe unit cell of okenite (CaO.2SiO2.2H2O) has been determined for a specimen from Bombay, India, using a combination of X-ray, electron-microscope, and electron-diffraction methods. It is anorthic with a 9·84, b 7·20, c 21·33Å., α 90·0°, β 103·9°, γ, 111·5°, elongation b, Z 9. These data are compatible with the goniometric results of Boggild (1922) and allow the latter to be interpreted.A specimen from Crestmore, California, which Eakle (1917) had described as okenite, was also examined. It was found to be a new species, having the same composition as okenite but distinguishable from it by its optical properties, X-ray powder data, and unit cell. The latter is anorthic with a 7·60, b 7·32, c 9·86 Å, α 111° 48′, β 86° 12′, γ 103° 54′, elongation b, Z = 3. Because of the relation to okenite, the name nekoite is suggested.

Indexed Powder Data for Incommensurate Bi2Sr2Ca2Cu3Oz

1992 ◽  
Vol 7 (1) ◽  
pp. 49-51 ◽  
Author(s):  
C. Namgung ◽  
E.E. Lachowski ◽  
J.T.S. Irvine ◽  
A.R. West
Keyword(s):  
Electron Diffraction ◽  
Unit Cell ◽  
Powder Pattern ◽  
Indexing Scheme ◽  
X Ray

AbstractThe X-ray powder pattern of the Pb-free 110 K superconductor phase Bi2Sr2Ca2Cu3Oz has many lines which belong to an incommensurate supercell. Using electron diffraction photographs as a guide, an indexing scheme for the powder pattern has been obtained. The unit cell has a geometrically orthorhombic subcell a = 5.411 (2), b = 5.420(2), c = 37.29(2) Å. Supercell reflections have indices that are derived from the subcell k, l indices by addition of ± q, where q = nδb + nεc: n = 1,2 …; ε = 0.211(2); ε = −0.78(1).

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