Powder Diffraction Investigations Research Articles

High resolution neutron powder diffraction investigation of temperature and pressure effects on the structure of the high-T c superconductor Y 2Ba 4Cu 7O 15

We have investigated the effect of temperature and 10 kbar pressure on the structure of the new high-temperature superconductor Y 2Ba 4Cu 7O 15 ( T c=68 K) in an attempt to relate the pressure dependence of T c in such materials to changes in certain Cu-O distances. The orthorhombic Ammm X-ray model of Bordet et al., with lattice constant c≈50.3 Å, has been confirmed by our high-resolution neutron powder diffraction measurements. The structure can be described as alternate layers of single CuO-chain (YBa 2Cu 3O 7) and double CuO-chain (YBa 2Cu 4O 8) blocks. The thermal expansion is anisotropic, with the b-axis, parallel to the single and double Cu-O chains, remaining approximately constant for T< T c. As in YBa 2Cu 4O 8, Cu-O distances bridging chains and planes, as well as Ba-O distancesare significantly changed by pressure. However, in Y 2Ba 4Cu 7O 15 these changes are different for the single and double CuO-chain layers. A correlation with the pressure dependence of T c is proposed.

Etude par diffraction neutronique de la phase Bi 12[Bi +V0,75V +V0,05□ 0,20]O 20 de structure sillenite

A neutron powder diffraction investigation of the γ-Bi 2O 3 derivative Bi 12[Bi +V 0,75V +V 0,05□ 0,20]O 20 using neutron diffraction profile analysis has been carried out. It crystallizes in the I23 space group with a = 10,265 Å. In the sillenite-type structure the tetrahedral sites are partially occupied by bismuth (V) and vanadium (V) cations, which confirms previous expectations of the authors concerning the γ-Bi 2O 3 type structure.

X‐ray powder diffraction investigations of solid solutions in the KClKBrH2O system at 298 K

AbstractThe measurements of crystal lattice parameters (a) of solid solutions being formed in the system KClKBrH2O at 298 K were conducted. The volumes (v) of unit cells and the densities (ϱ) of mixed crystals K(Cl, Br) were calculated. It was confirmed that in the investigated system continuous solid solutions were formed. The lattice parameters of these crystals formed from aqueous solutions of salts as well as from molten salts and also calculated by Durham‐Hawkins method were nearly identic.

Crystal Structure of Orthorhombic Zirconia in Partially Stabilized Zirconia

A neutron powder diffraction investigation confirms that, in tough magnesiapartially‐stabilized zirconia cooled to 30 K, most of the tetragonal zirconia transforms to an orthorhombic phase. This phase is retained on heating to room temperature; the lattice parameters at 295 K are a = 0.5068, b = 0.5260, and c = 0.5077 nm. The room‐temperature crystal structure (space group Pbc21) is determined by multiphase Rietveld refinement from the neutron diffraction pattern. This orthorhombic structure is compared with the parent tetragonal structure and with the structure of monoclinic zirconia, which it closely resembles.

Superconducting Tl 2.0Ba 2.0CuO 6+δ: A high resolution neutron powder and single crystal x-ray diffraction investigation

The structure of the orthorhombic form of Tl 2Ba 2CuO 6+δ( T c=90 K), synthesized in sealed gold tubes using BaO 2, has been refined using high resolution neutron powder diffraction data collected at 4 K. No significant deficiency in metal stoichiometry could be inferred from the crystal structure analysis. The space group (Fmmm) used in this study gives essentially the same results as the alternative (Abma, Amaa) proposed in earlier work. The large amount of disorder that exists in the Tl 2O 2-slab is mirrored in the large thermal parameters for this structural unit compared to those for the CuO 2 sheet. A site at ( built1 4 built1 4 built1 4 ) is occupied by an amount of oxygen to give overall stoichiometry Tl 2Ba 2CuO 6.10, suggesting that oxygen non-stoichiometry plays an important role in producing high T c superconductivity in this system. Analysis of single crystal X-ray diffraction data of tetragonal Tl 2Ba 2CuO 6+ δ is totally consistent with the neutron powder diffraction results.

X‐ray powder diffraction investigations of solid solutions with limited miscibility in the KNO3NH4NO3H2O system at 298 K

AbstractThe measurements of crystal lattice parameters (a, b, c) were conducted and the volumes (v) of unit cells of solid solutions forming in the system KNO3NH4NO3H2O at 298 K were calculated. It was established that in this system at 298 K two series of solid solutions were formed: the mNH4NO3 · n(KNO3 · 2 NH4NO3) solid solution with the gap of miscibility and the kKNO3 · l(KNO3 · 2 NH4NO3) solid solution with one‐sided limited miscibility.

Thermoanalytical and x-ray diffraction investigations of Ba 2Cu 3O 5+d for preparation of Y-Ba-Cu-O superconductors

Thermogravimetric (TG) measurements and differential thermoanalysis (DTA) were carried out connected with X-ray powder diffraction investigations of Ba 2Cu 3O 5+ d samples prepared at different temperatures. A low temperature tetragonal phase with higher oxygen content and a high temperature tetragonal phase could be distinguished with lattice constants a = 16.19 Å and 12.96 Å, and c = 12.38 Å and 9.16 Å, respectively. A possible mechanism for selective preparation of superconductors from high temperature phase has also been proposed assuming a structure with space group P4 2/mcm.

A Time-Resolved Neutron and X-Ray Powder Diffraction Investigation of Reactions between Ca12Al14O33, CaCl2, CaBr2 and Water.

Etude de l'effet des additifs CaCl 2 et CaBr 2 sur la reaction entre Ca 12 Al 14 O 33 et l'eau. L'hydrolyse est plus rapide en presence de CaCl 2 et CaBr 2 que dans l'eau pure

ChemInform Abstract: Phase Relationships in the Ternary System Ti‐Au‐Al at 775 K

Abstracthave been investigated by means of X‐ray powder diffraction, DTA, metallographic and microhardness investigations.

Caracterisation et localisation de la molecule de para-xylene dans une zeolithe pentasil : Cas des complexes formes par deux boralites avec le para-xylene

Precise X-ray powder diffraction investigations on pentasil type zeolites having respectively the H 1.4B 1.36Al 0.02Si 94.6O 192 and H 3.2B 3.2Al 0.02Si 92.8O 192 compositions reveal that the visual modifications observed on the step-scan profiles can be interpreted by localizing the centroid of the p-xylene molecule on the mirror plane of the 4c site in the Pnma space-group. Among the three possible orientations of the p-xylene molecule, the best fit is obtained for the solution where the line joining the methyl groups is parallel to the straight channel. Several trial and error calculations show that the organic molecule might present a statistical disorder with two simultaneous orientations in the channels.

ChemInform Abstract: Neutron Powder Diffraction Investigation of Deuterated Pd15P2.

AbstractWith the aid of crystal structure refinements of pure and deuterated Pd,5P2 (Rietveld‐type profile analysis of neutron powder diffraction intensities) the positions and the degree of occupancy for the dissolved Datoms are determined at 296 Kand 500kPa deuterium pressure.

A time-resolved neutron powder diffraction investigation of the hydration of CaSO4.1/2D2O and of the dehydration of CaSO4.2D2O

A chemical reaction, the hydration of CaSO4.½D2O, was followed in real time in an on-line neutron diffraction experiment at different temperatures. The results of the reactions are presented as diagrams showing the evolution of the intensities of CaSO4.2D2O in real time. The hydration passes through the formation of a gel interphase. The dehydration of CaSO4.2D2O was followed in the same way at temperatures up to 420 K.

A Neutron Powder Diffraction Investigation of Deuterated Pd15P2*

A Neutron Powder Diffraction Investigation of Deuterated Pd₁₅P₂*

A neutron powder diffraction investigation of deuterated Pd15P2

A neutron powder diffraction investigation of deuterated Pd₁₅P₂

A neutron powder diffraction investigation of lanthanum hexaboride

A neutron powder diffraction investigation of lanthanum hexaboride

Neutron powder diffraction investigations of hydrogenated Pd 3P 0.80 and Pd 6P

Etude cristallographique des composes du type Pd 3 P 0,80 H 0,17 et Pd 6 PH 0,39 . Le premier compose cristallise dans le groupe Pnma. La structure est formee de prismes triangulaires de Pd 6 avec un atome de P dans chaque centre. Les hydrogenes occupent les memes positions que le deuterium dans Pd 3 P 0,80 D 0,15 . Le deuxieme cristallise dans P 21 /C

Rubification of Terrae Rossae in Slovakia: A Mössbauer Effect Study

AbstractMineralogical and 57Fe Mössbauer spectroscopic analyses were made on seven terrae rossae and two terrae fuscae samples of Pliocene to Early Pleistocene age from Slovakia and limestone residues from their parent materials. In most of the samples, no mineral weathering or clay mineral formation could be detected by optical or X-ray powder diffraction investigation, compared with their parent limestone residues; only one terra rossa showed a strong weathering of primary feldspar and phyllosilicates and a high rate of clay formation, especially kaolinite. Mössbauer measurements between 5° and 300°K showed that hematite and goethite are the dominant color pigments in the rubified terrae rossae and their corresponding limestone residues. The mean particle size of hematite and goethite was estimated from Mössbauer effects and X-ray powder diffraction data to be 95 and 250 Å, respectively. Reduced values of the hyperfine fields at 5°K of the soil iron oxides, as compared with those of the pure oxides, indicate a partial substitution of Fe(III) by Al. The hematite content correlates with the Munsell color notation of 5 of the 7 terrae rossae samples and their corresponding limestone residues. All terrae rossae samples showed higher hematite contents than their corresponding limestone residues, indicating that the rubification of such materials is independent of the degree of weathering.

X-ray powder diffraction investigation of naphthalene up to 0.5 GPa

X-ray powder diffraction investigation of naphthalene up to 0.5 GPa

Structural phase transitions in ferroelastic RbAlF4. I. DSC, X-ray powder diffraction investigations and neutron powder profile refinement of the structures

The layer compound RbAlF4 is shown to undergo structural phase transitions at 553K and 282K under investigation by DSC and X-ray powder diffraction. The structures of the three phases are determined by neutron powder profile refinement. The high-temperature phase has the ideal TlAlF4 structure P4/mmm which corresponds to the tilt system a0a0c0. The intermediate room-temperature phase is confirmed as P4/mbm, the tilt system is a0a0c+. The low-temperature phase is consistent with the space group Pmmn which corresponds to both ap +b0c+ (near the transition temperature) and ap +bp +c+ (at very low temperature). The 553K phase transition is a non-ferroic phase transition while the 282K transition is ferroelastic. According to Aizu the low-temperature phase is a 4/mmmFmmm species. The temperature behaviour of the structural parameters is discussed, particularly in the framework of ferroelasticity.

Synthesis and crystal structures of Ba 2Re 6S 11 and Sr 2Re 6S 11, compounds containing [Re 6S 8] clusters

The ternary sulphides Ba 2Re 6S 11 and Sr 2Re 6S 11 were synthesized by the reaction of the alkaline earth carbonates with rhenium at 1350 °C and 1450 °C respectively in a stream of H 2S. X-ray investigations on single crystals gave the structure of Ba 2Re 6S 11. The atomic arrangement consists of a framework in which [Re 6S 8] clusters are linked in three dimensions according to the formulation { Re 6S 8]S 6 2 } 4− . The barium ions are inserted in holes of this framework. Powder diffraction investigations showed that Sr 2Re 6S 11 has a structure analogous to that of Ba 2Re 6S 11. Measurements of the magnetic susceptibilities between 3.7 and 295 K show that Ba 2Re 6S 11 has a diamagnetic behaviour. The distortion of [M 6X 8] clusters is discussed with respect to electronic configuration.