Crystal Structures and Superconductivity in the La1.5−xBa1.5+Cu7+ySystem

1987 ◽  
Vol 99 ◽  
Author(s):  
JE. Greedan ◽  
A. H. O'Reilly ◽  
C. V. Stager ◽  
F. Razavi ◽  
W. Abriel
Keyword(s):  
Crystal Structures ◽  
Variable Temperature ◽  
Meissner Effect ◽  
Powder Diffraction Data ◽  
Solution System ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Solid Solution System ◽  
Copper Valence ◽  
Flowing Oxygen

ABSTRACTMembers of the solid solution system La1.5−xBa1.5+Cu7+ywith x = 0, 0.125, 0.25. 0.375 and 0.5 have been prepared both in air and under one atmosphere of flowing oxygen. In general, except for x =0, the oxygen annealed compounds are superconducting while the air-annealed samples are semiconductors. Tc's measured by Meissner effect and resistivity data range to 70K. The crystal symmetry in all cases is apparently tetragonal as verified for x = 0.375 by variable temperature Guinier x-ray experiments at temperatures down to 8K. Crystal structures have been refined from neutron powder diffraction data. A correlation is noted between Cu-0 distances which connect adjacent Cu planes - the average copper valence and the occurrence of superconductivity.

Anti-KSbF6 structure of CaTbF6 and CdTbF6: a confirmation of the singular crystal chemistry of Tb4+ in fluorides

2005 ◽  
Vol 61 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Michaël Josse ◽  
Marc Dubois ◽  
Malika El-Ghozzi ◽  
Joël Cellier ◽  
Daniel Avignant
Keyword(s):  
Crystal Structures ◽  
Three Dimensional ◽  
Chemical Properties ◽  
Neutron Powder Diffraction ◽  
Fluoride Ion ◽  
Crystal Chemical ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Simple Cubic

The crystal structures of two new tetravalent terbium fluorides, CaTbF6 and CdTbF6, have been determined from X-ray and neutron powder diffraction data. The title compounds exhibit an anti-KSbF6 structure, the three-dimensional framework of which is built of [TbF6]2− chains of edge-sharing dodecahedra further linked, by sharing corners, to isolated [MF6]4− octahedra (M = Ca, Cd). The mechanism of the anionic sublattice rearrangement when going from KSbF6 to CaTbF6 is described and related to a simple cubic fluoride-ion packing. Comparison with the crystal structures of β-BaTbF6 and other representatives of the M II M^{\prime \rm IV}F6 family allows the singular crystal-chemical properties of some fluoroterbates to be emphasized.

Crystal structures of tricalcium citrates

2018 ◽  
Vol 33 (2) ◽  
pp. 98-107 ◽  
Author(s):  
James A. Kaduk
Keyword(s):  
Crystal Structures ◽  
Density Functional ◽  
Three Dimensional ◽  
Water Molecules ◽  
Calcium Citrate ◽  
Powder Diffraction Data ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Calcium Supplements ◽  
Dimensional Network

The crystal structures of calcium citrate hexahydrate, calcium citrate tetrahydrate, and anhydrous calcium citrate have been solved using laboratory and synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Both the hexahydrate and tetrahydrate structures are characterized by layers of edge-sharing Ca coordination polyhedra, including triply chelated Ca. An additional isolated Ca is coordinated by water molecules, and two uncoordinated water molecules occur in the hexahydrate structure. The previously reported polymorph of the tetrahydrate contains the same layers, but only two H2O coordinated to the isolated Ca and two uncoordinated water molecules. Anhydrous calcium citrate has a three-dimensional network structure of Ca coordination polyhedra. The new polymorph of calcium citrate tetrahydrate is the major crystalline phase in several commercial calcium supplements.

The crystal structures of solvent-free alkali-metal squarates from powder diffraction data

2005 ◽  
Vol 220 (11) ◽  
Author(s):  
Robert E. Dinnebier ◽  
Hanne Nuss ◽  
Martin Jansen
Keyword(s):  
High Resolution ◽  
Alkali Metal ◽  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Solvent Free ◽  
Crystallographic Data ◽  
Powder Diffraction Data ◽  
X Ray

AbstractThe crystal structures of solvent-free lithium, sodium, rubidium, and cesium squarates have been determined from high resolution synchrotron and X-ray laboratory powder patterns. Crystallographic data at room temperature of Li

Inorganic crystal structures from powder data—A retrospection

1999 ◽  
Vol 14 (1) ◽  
pp. 5-9 ◽  
Author(s):  
L’ubomír Smrčok ◽  
Ján Mailing
Keyword(s):  
Short Review ◽  
Powder Diffraction Data ◽  
Interatomic Distances ◽  
X Ray ◽  
Space Groups ◽  
Neutron Powder Diffraction Data ◽  
Inorganic Crystal ◽  
Reported Data ◽  
Atomic Coordinates ◽  
Icsd Database

More than 10 000 inorganic structures based on both X-ray and neutron powder diffraction data were extracted from the ICSD database and analyzed considering overall trends, cell symmetries, occurrence of the space groups, complexity, precision and reliability of reported data. It was found that the major amount of structures belong to higher symmetries and have 2–5 atoms in the asymmetric unit. Less than 35% of the e.s.d.'s of atomic coordinates is ≤10−3 and 10−4 or better was reached in only 5% of cases. Approximately one-quarter of papers contain possibly inaccurate atomic coordinates or interatomic distances. A short review of journals publishing structures derived from powders is also given.

The BaAl4 Structure and its Derivatives from the R-Zn-Ga Systems

2012 ◽  
Vol 194 ◽  
pp. 5-9 ◽  
Author(s):  
Yuriy Verbovytskyy ◽  
Antonio Pereira Gonçalves
Keyword(s):  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray ◽  
First Time

Seven new ternary RZn1+xGa3-x (R = Ce, Pr, Nd, Sm, Ho and Er) and R5Zn2Ga17 (R = Ce) phases are synthesized for the first time. Their crystal structures are solved on basis of X-ray powder diffraction data. The above mentioned compounds belong to the BaAl4 (space group I4/mmm) and Rb5Hg19 (space group I4/m) structure types. Details of the structure of the Ce5Zn2Ga17 compound and relationship with RZn2-xGa2+x (BaAl4 type) and R3Zn8-xGa3+x (La3Al11 type) are briefly discussed.

scholarly journals Pressing the Limits of Rietveld Refinement

1988 ◽  
Vol 41 (2) ◽  
pp. 297 ◽  
Author(s):  
RA Young
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Structure Refinement ◽  
Site Occupancy ◽  
The Other ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Refinement Method

Two examples are given, one with X-ray data and one with netltron data, of the determination of structural detail which appear to be at the edge of current possibility for the Rietveld structure-refinement method. In the first example, 2�2 wt% Sb substituted in CalO(P04)6F2 was located. X-ray powder diffraction data collected with special attention to intensity precision and scale constancy were used. The problem was solved through comparison of intra-sample site-occupancy ratios between Sb-doped and undoped samples. In the second example, high quality, high resolution neutron powder diffraction data were required. The problem was to distinguish between two subtly different models of kaolinite for which the R-weighted-pattern values differed only by 2 or 3 units in the third digit and, particularly, to understand the basis for the consistent programmatic choice of one of the models (PI) over the other. The answer was found in the calculated and 'observed' intensities for (h+ k)-odd reflections; although they were very small, less than 1% of the intensities of the main reflections, many of them were distinctly nonzero. Even though these reflections were not separately observable, because of overlap and small size, they nonetheless correlated with one model sufficiently better than the other to produce the consistent choice.

BaCeN2, ein Bariumnitridocerat(IV) mit einer Struktur vom anti-TiP-Typ / BaCeN2, a Bariumnitridocerate(IV ) with a Structure of the anti-TiP Type

1994 ◽  
Vol 49 (9) ◽  
pp. 1169-1174 ◽  
Author(s):  
Oliver Seeger ◽  
Joachim Strähle
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Neutron Powder Diffraction ◽  
Type Structure ◽  
Stoichiometric Ratio ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Moisture Sensitive ◽  
Trigonal Prismatic

Reaction of Ba3N2 with CeN in the stoichiometric ratio 1:3 at 850 °C under an atmosphere of N2 followed by quenching yields air and moisture sensitive BaCeN2. The product crystallizes isotypically to β-RbScO2 with the anti-TiP type structure in the hexagonal space group P63/mmc with a = 365.06(2), c = 1266.03(3) pm, Z = 2. The structure was determined using X-ray and neutron powder diffraction data. In the structure the Ba2+ cations occupy trigonal prismatic holes with distances Ba-N = 288(1) pm while the Ce atoms are in octahedral positions with distances C e -N = 242.4(8) pm

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