scholarly journals Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

1998 ◽  
Vol 62 (3) ◽  
pp. 341-353 ◽  
Author(s):  
Roger H. Mitchell ◽  
Anton R. Chakhmouradian
Keyword(s):  
Infrared Transmission ◽  
X Ray Diffraction ◽  
Alkaline Complex ◽  
X Ray ◽  
Naturally Occurring ◽  
Accessory Phase ◽  
Diffraction Patterns ◽  
A Site ◽  
Perovskite Type ◽  
Low Symmetry

AbstractTh-rich (up to 18.4 wt% ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na0.39LREE0.19Th0.12Ca0.05Sr0.02)Σ0.77(Ti0.76Nb0.27)Σ1.03O3. The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi2O6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (Å) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) Å. The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations (‘ceriobetafite’). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE2O3 and ThO2 contents. Both ‘ceriobetafite’ and belyankinite were formed due to metasomatic alteration of loparite.

Structure analysis of CaTi1−xSnxO3 (x = 0.0–1.0) solid solutions

2014 ◽  
Vol 29 (3) ◽  
pp. 254-259 ◽  
Author(s):  
Naoki Takani ◽  
Hisanori Yamane
Keyword(s):  
Solid State ◽  
Solid Solutions ◽  
Solid State Reaction ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Perovskite Type ◽  
Perovskite Type Structure

CaTi1−xSnxO3 (x = 0.0–1.0) solid solutions were prepared by solid-state reaction at 1450 °C. Rietveld refinement of their powder X-ray diffraction patterns revealed that all the solid solutions crystallized in orthorhombic cells with the perovskite-type structure, the space group Pbnm. The refined unit-cell parameters linearly increased with nominal tin contents x.

Powder diffraction analysis of an interstratified marcasite/pyrite structure

1995 ◽  
Vol 10 (3) ◽  
pp. 198-203 ◽  
Author(s):  
Neil E. Johnson ◽  
Sidney S. Pollack ◽  
Elizabeth A. Frommell ◽  
Patricia A. Eldredge
Keyword(s):  
Catalytic Activity ◽  
Stacking Faults ◽  
Catalyst Precursor ◽  
X Ray Diffraction ◽  
Aromatic Rings ◽  
X Ray ◽  
Naturally Occurring ◽  
Benzylic Carbon ◽  
Diffraction Peaks ◽  
Diffraction Patterns

A synthetic catalyst precursor formed by sulfiding ferrihydrite (Fe3+O(OH)) in the presence of a hydrogen donor produces X-ray diffraction patterns resembling a mixture of both naturally occurring FeS2 polymorphs marcasite and pyrite. The diffraction peaks display a differential broadening, however, wherein only those peaks coincident to both marcasite and pyrite are strong and sharp, a feature that cannot be accounted for by a simple physical mixture. The broadening is analogous to that found in hexagonal cobalt, where occasional stacking faults produce interstratification of the hexagonal and cubic close-packed forms, resulting in strongly coherent diffraction only along the stacking direction. The crystal structures of marcasite and pyrite are virtually identical if viewed perpendicular to the (101) and (001) planes, respectively. Calculation of diffraction patterns based upon models of interstratifying marcasite and pyrite layers along these planes demonstrates that a sequence with marcasite-to-pyrite and pyrite-to-marcasite stacking fault probabilities of 0.22 provides a good fit to the experimental pattern. This interstratified material is a precursor to a species that shows catalytic activity for cleaving C-C bonds between aromatic rings and benzylic carbon atoms at low (<350 °C) temperatures.

Lead-bearing phyllotungstite from the Clara mine, Germany with an ordered pyrochlore–hexagonal tungsten bronze intergrowth structure

2013 ◽  
Vol 77 (1) ◽  
pp. 57-67 ◽  
Author(s):  
I. E. Grey ◽  
W. G. Mumme ◽  
C. M. MacRae
Keyword(s):  
Tungsten Bronze ◽  
Partial Ordering ◽  
X Ray Diffraction ◽  
Black Forest ◽  
X Ray ◽  
Pyrochlore Type ◽  
Diffraction Patterns ◽  
A Site ◽  
Clara Mine ◽  
The Ideal

AbstractLead-bearing phyllotungstite from the Clara mine in the central Black Forest, Germany has a formula (Cs0.41)Na0.14K0.05Pb2+2.01Ca0.26[W6+10.87Fe3+3.13O35.75(OH)6.25](O(H2O)3). X-ray diffraction patterns exhibit pseudohexagonal symmetry, but refinement of single-crystal synchrotron data has shown that the true symmetry is orthorhombic, Cmcm, with a = 7.298(1), b = 12.640(2), c = 19.582(4) Å, and that the pseudohexagonal character is due to submicrometre-scale cyclical twinning by rotation about the pseudohexagonal c axis. The structure can be described in terms of an ordered intergrowth, parallel to (001), of (111)py blocks with pyrochlore-type structures, which are ~6 Å in width, and two-layer wide regions with a hexagonal tungsten bronze (HTB) type structure. Caesium atoms occupy 18-coordinate cavities in the HTB regions, and H2O molecules occupy Φ sites in the A2B2O6Φ pyrochlore blocks. The lowering of symmetry from hexagonal to orthorhombic is due to partial ordering of W and Fe in the octahedral B sites and of Pb and vacancies in the A sites of the pyrochlore blocks. The ideal formula for the intergrowth structure (with no vacancies) is C 2A10[B14(O,OH)42]Φ4, where C is the cavity site in the HTB slabs. The mineral has only 21% occupancy of the C site and 25% occupancy of the A site, but full occupancy of the Φ site. There may be some mixing of Cs and H2O between the C and Φ sites.

scholarly journals Revision of the Li13Si4structure

2013 ◽  
Vol 69 (12) ◽  
pp. i81-i82 ◽  
Author(s):  
Michael Zeilinger ◽  
Thomas F. Fässler
Keyword(s):  
Site Occupancy ◽  
Careful Analysis ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Structure Report ◽  
Diffraction Patterns ◽  
Atomic Displacement Parameters ◽  
A Site

Besides Li17Si4, Li16.42Si4, and Li15Si4, another lithium-rich representative in the Li–Si system is the phase Li13Si4(tridecalithium tetrasilicide), the structure of which has been determined previously [Franket al.(1975).Z. Naturforsch. Teil B,30, 10–13]. A careful analysis of X-ray diffraction patterns of Li13Si4revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li13Si4on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i) the introduction of a split position for one Li site [occupancy ratio 0.838 (7):0.162 (7)], (ii) the anisotropic refinement of atomic displacement parameters for all atoms, and (iii) a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li13Si4contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si–Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in theabplane atz= 0 and are strictly separated from the Si–Si dumbbells atz= 0.5.

PROPERTIES OF GADOLINIUM-DOPED PZT (Zr:Ti=52:48)

2002 ◽  
Vol 16 (23) ◽  
pp. 3515-3525 ◽  
Author(s):  
S. BOONYUEN ◽  
L. PDUNGSAP ◽  
P. WINOTAI ◽  
T. SUDYOADSUK ◽  
P. PETCHPONG
Keyword(s):  
Dissipation Factor ◽  
Esr Spectra ◽  
X Ray Diffraction ◽  
Mole Percent ◽  
X Ray ◽  
Maximum Value ◽  
Drastic Effect ◽  
Diffraction Patterns ◽  
A Site ◽  
Dielectric And Piezoelectric Properties

PZT(Zr:Ti=52:48) ceramics can be modified by Gd 3+, giving compositions Pb 1-x Gd x- ( Zr 0.52 Ti 0.48)1-x/4 O 3 with x = 0.00, 0.01, 0.5, 1, 2, 6 and 10 mole percent. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole percent Gd at which impurity unreacted oxides start to appear. ESR spectra of PGZT's indicate that Gd 3+ can enter both A and B sites of the perovskite structure instead of only A site as widely believed. As a result, the tetragonality (c/a ratio) first increases and reaches a maximum at x ≅ 0.8 mole percent and drops as Gd 3+ enters more A sites. The doping should, however be limited to one mole percent as overdoping proves detrimental to the dielectric and piezoelectric properties of PGZT. The dielectric constant (1 kHz) of the poled samples reaches a maximum value of 1150 at x = 0.02 while the largest d33 value of 160 pC/N is achieved at only lightly doped 0.01 mole percent. Furthermore, the Gd doping has a drastic effect on Qm and the dissipation factor DF — the former drops sharply while the latter increases with x.

New Directions in the X-Ray Diffraction Analysis of Organic Materials

1991 ◽  
Vol 35 (A) ◽  
pp. 653-660
Author(s):  
Ron Jenkins
Keyword(s):  
Poor Quality ◽  
Inorganic Materials ◽  
X Ray Diffraction ◽  
Large Unit ◽  
X Ray ◽  
Angle Data ◽  
New Directions ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Low Symmetry

AbstractThe analysis of crystalline organic phases by X-ray powder diffraction presents special problems, beyond those typically associated with inorganic materials. The large unit cells often associated with organic compounds, combined with the low symmetry of the structures, give rather complicated diffraction patterns which contain many low angle lines. The Bragg-Brentano geometric arrangement employed in most commercial diffractometers gives maximum d-spacing error at low diffraction angles. This, in turn, means that not only can the large d-spacing data be of poor quality, but also that much of the low angle data required for the indexing of the pattern is subject to large errors.

The crystal structure of graphite-bromine compounds

1965 ◽  
Vol 283 (1393) ◽  
pp. 179-193 ◽  
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Detailed Analysis ◽  
Single Crystals ◽  
The Other ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Naturally Occurring ◽  
Diffraction Patterns

Single crystals of naturally occurring graphite which had been treated with bromine vapour have been examined by electron and X-ray diffraction and also by electron microscopy. The intercalated bromine is in the form of layers, interleaved between the graphite layers in a sequence which is dependent upon the concentration of bromine. The structure within a bromine layer is relatively highly ordered and has been shown to take on two forms, one which occurs at concentrations in excess of 47 (wt.) %, the other occurs at lower concentrations. Detailed analysis of the diffraction patterns given by the lower concentration form suggest that it is composed of chains of Br 2 molecules, in which the interatomic distances are virtually identical with those of solid bromine.

Ferroelectricity in SrTiO3 Ceramics Induced by Pr Doping

2004 ◽  
Vol 848 ◽  
Author(s):  
A. Durán ◽  
E. Martínez ◽  
J. Mata ◽  
J. Heiras ◽  
X. Solans ◽  
...  
Keyword(s):  
Single Phase ◽  
Temperature Differential ◽  
X Ray Diffraction ◽  
Ionic Radii ◽  
Ferroelectric State ◽  
X Ray ◽  
The Difference ◽  
Diffraction Patterns ◽  
A Site ◽  
Srtio3 Ceramics

ABSTRACTFerroelectricity was induced in SrTiO3 by the Sr exchange for Pr ion in the A site of the perovskite ABO3-type structure. X-ray diffraction patterns show single phase crystalline structure in the SrxPr1-xTiO3 compound for x=0, 0.025, 0.050, 0.075 and 0.1 compositions. Rietveld refinement shows that the unit cell volume decreases with the increasing of Pr content as a consequence of the difference between Sr/Pr ionic radii. Furthermore, high-temperature differential thermoanalysis (DTA) displays a small anomaly at about 118 °C which is probably due to the Pr ion producing a distortion of the perovskite structure via an off-center site. This deformation in the lattice induces a measurable polar behavior of the solid solution. Dielectric permittivity (ε vs T) measurements display a well defined peak at about 238 °C. Furthermore, a well defined hysteresis loop at 30 °C with a remnant polarization that tends to decrease with increasing Pr concentration is observed. Both experimental results confirm the ferroelectric state induced by the Pr ion.

High Resolution Replication of Organoclay Surfaces

1982 ◽  
Vol 40 ◽  
pp. 576-577
Author(s):  
W. W. Barker ◽  
W. E. Rigsby ◽  
V. J. Hurst ◽  
W. J. Humphreys
Keyword(s):  
Clay Mineral ◽  
Organic Molecule ◽  
Organic Molecules ◽  
X Ray Diffraction ◽  
Xrd Pattern ◽  
X Ray ◽  
Naturally Occurring ◽  
Silicate Layers ◽  
Mineral Identification

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.

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