SUBSTITUTION EFFECT IN Pr-DOPED YBCO

2006 ◽  
Vol 20 (20) ◽  
pp. 2899-2907
Author(s):  
L. ZHANG ◽  
M. WANG ◽  
Y. Y. XU
Keyword(s):  
Rietveld Refinement ◽  
Reference System ◽  
Structural Changes ◽  
Substitution Effect ◽  
Bond Valence ◽  
X Ray Diffraction ◽  
Dc Magnetization ◽  
X Ray ◽  
Bond Lengths ◽  
Bond Valence Sum

A series of samples of Y 1-x Pr x Ba 2 Cu 3 O y ( YPrBCO ) with 0.05 ≤ x ≤ 0.6 was synthesized and characterized by DC magnetization, X-ray diffraction (XRD), and Rietveld refinement. It is found that besides Pr substitution for Y , a part of Pr substituted for Ba in YBa 2 Cu 3 O y (YBCO), and the amount of Pr in the Y and Ba positions, respectively, is estimated by the refinement with the help of bond valence sum (BVS) calculation. By comparing the correlation of structural changes such as Ba-O (4) and Cu (1, 2)- O (4) bond lengths and superconductivity between our system with the reference system where Pr just replaces Y , structural evidences are found to explain Pr substitution for Ba suppresses Tc more strongly than that for Y .

Simultaneous Substitution of Y and Ba by Ca in YBCO

2007 ◽  
Vol 546-549 ◽  
pp. 2123-2126
Author(s):  
L. Zhang ◽  
Jing Yu ◽  
Han Zhang
Keyword(s):  
Rietveld Refinement ◽  
Structural Changes ◽  
Close Correlation ◽  
Careful Analysis ◽  
Experimental Results ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Ca Substitution ◽  
Simultaneous Substitution

A series of samples of Y1-xCaxBa2Cu3Oy (YCBCO) were synthesized with 0.05≤x≤0.3 and characterized by DC magnetization, X-ray diffraction (XRD), and Rietveld refinement. It was found that Ca replaces Y and Ba in YBa2Cu3Oy (YBCO) simultaneously, and the amount of Ca in the Y and Ba positions is estimated by the refinement，respectively. The experimental results showed that the structural changes had a close correlation with Tc. With careful analysis of the change of the Tc below and above x=0.2 and the changes of the bond lengths, such as Cu(2)-O(2) and Cu(2)-O(3), it is suggested that the Ca substitution for Y suppresses the Tc more strongly than that for Ba.

X-ray diffraction study of poly crystalline Y2BaO4: a test of the new EXPO program

1999 ◽  
Vol 214 (4) ◽  
Author(s):  
V. Massarotti ◽  
D. Capsoni ◽  
M. Bini ◽  
A. Altomare ◽  
A. G. G. Moliterni
Keyword(s):  
Diffraction Study ◽  
Rietveld Refinement ◽  
Direct Methods ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Orthorhombic Cell

AbstractIn order to test the new EXPO program, anAn orthorhombic cell (On the basis of accurate atomic fractional coordinates determined by direct methods application and Rietveld refinement, bond lengths and angles have been estimated and discussed with respect to the data of the isotypic Y

Thermal behaviour of alum-(K) KAl(SO4)2·12H2O from in situ laboratory high-temperature powder X-ray diffraction data: thermal expansion and modelling of the sulfate orientational disorder

2015 ◽  
Vol 79 (1) ◽  
pp. 157-170 ◽  
Author(s):  
Paolo Ballirano
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Diffraction Data ◽  
Bond Valence ◽  
X Ray Diffraction ◽  
Orientational Disorder ◽  
X Ray ◽  
Disorder Parameter ◽  
Bond Valence Sum

AbstractThe present work analyses the thermal behaviour of alum-(K), KAl(SO4)2·12H2O, by in situ laboratory high-temperature powder X-ray diffraction data from 303 K to melting, which starts at 355 K and is completed, due to kinetics, at 359 K. The calculated a0 linear thermal expansion coefficient is of 14.68(11) × 10–6 K–1 within the investigated thermal range. The k disorder parameter, describing the extension of the orientational disorder of the sulfate group, has been found to decrease from ∼0.70 to ∼0.65 just before melting. It has been demonstrated that the occurrence of the disorder implies the coexistence of K+ ions in both six- and seven-fold coordination. This is necessary for assigning a reasonable bond-valence sum of 0.81 valence units (vu) to the 'average' K+ ion a instead of 0.66 vu, which is obtained in the case of six-fold coordination alone. We can describe the temperature dependence of k from 93–355 K by means of the empirical equation k = 0.798(12) + 2.5(11) × 10–4 T – 1.9(2) × 10–6T2, which includes reference low-temperature data. Bond-valence analysis has shown that, on cooling, an increase of the k disorder parameter and shortening of the K–O2 bond distance act together to maintain constancy in the bond-valence sum at the K site, stabilizing the structure. Therefore, the need for keeping the 'average' K+ ion at a reasonable bond-valence sum appears to be the driving force for the ordering process involving the sulfate group.

scholarly journals Sodium rubidium hydrogen citrate, NaRbHC6H5O7, and sodium caesium hydrogen citrate, NaCsHC6H5O7: crystal structures and DFT comparisons

2019 ◽  
Vol 75 (2) ◽  
pp. 223-227 ◽  
Author(s):  
Andrew J. Cigler ◽  
James A. Kaduk
Keyword(s):  
Hydrogen Bonds ◽  
Density Functional ◽  
Bond Valence ◽  
X Ray Diffraction ◽  
Bond Energies ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Axis Direction ◽  
Bond Valence Sum ◽  
Hydrogen Bond Energies

The crystal structure of sodium rubidium hydrogen citrate, NaRbHC6H5O7 or [NaRb(C6H6O7)] n , has been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. This compound is isostructural to NaKHC6H5O7. The Na atom is six-coordinate, with a bond-valence sum of 1.16. The Rb atom is eight-coordinate, with a bond-valence sum of 1.17. The distorted [NaO6] octahedra share edges to form chains along the a-axis direction. The irregular [RbO8] coordination polyhedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other Rb atoms, resulting in triple chains along the a-axis direction. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O...O distances are 2.426 and 2.398 Å. The Mulliken overlap populations in these hydrogen bonds are 0.140 and 0.143 electrons, which correspond to hydrogen-bond energies of about 20.3 kcal mol−1. The crystal structure of sodium caesium hydrogen citrate, NaCsHC6H5O7 or [NaCs(C6H6O7)] n , has also been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. The Na atom is six-coordinate, with a bond-valence sum of 1.15. The Cs atom is eight-coordinate, with a bond-valence sum of 0.97. The distorted trigonal–prismatic [NaO6] coordination polyhedra share edges to form zigzag chains along the b-axis direction. The irregular [CsO8] coordination polyhedra share edges with the [NaO6] polyhedra to form layers parallel to the (101) plane, unlike the isolated chains in NaKHC6H5O7 and NaRbHC6H5O7. A prominent feature of the structure is the chain along [100] of very short, very strong O—H...O hydrogen bonds; the refined O...O distances are 2.398 and 2.159 Å, and the optimized distances are 2.398 and 2.347 Å. The Mulliken overlap populations in these hydrogen bonds are 0.143 and 0.133 electrons, which correspond to hydrogen-bond energies about 20.3 kcal mol−1.

scholarly journals Structure of strontium tellurite glass, anti-glass and crystalline phases by high-energy X-ray diffraction, reverse Monte Carlo and Rietveld analysis

2020 ◽  
Vol 76 (1) ◽  
pp. 108-121 ◽  
Author(s):  
Rajinder Kaur ◽  
Atul Khanna ◽  
Hirdesh ◽  
Ann-Christin Dippel ◽  
Olof Gutowski ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Rietveld Refinement ◽  
Short Range ◽  
Bond Angle ◽  
High Energy ◽  
Reverse Monte Carlo ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Atomic Pair

The structures of xSrO–(100 − x)TeO2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, anti-glass and crystalline samples were studied by high-energy X-ray diffraction (HEXRD), reverse Monte Carlo (RMC) simulations, atomic pair distribution function analysis and Fullprof Rietveld refinement. The atomic pair distributions show the first peak at 1.90 Å due to the Te—O equatorial bonds and the Te—O peak is asymmetrical due to the range of Te—O bond lengths in glass, anti-glass and crystalline samples. The short-range structural properties of glasses such as Te—O bond lengths, Te–O speciation, Te–Te distances and O—Te—O bond angle distributions were determined by RMC simulations. The average Te–O coordination number (N Te–O) for 5SrO–95TeO2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in N Te–O revealed that the glass network predominantly contains TeO4 units with a small amount of TeO3 units and there is a structural transformation TeO4 → TeO3 with an increase in SrO concentration. The O—Te—O bond angle distributions have a peak at 79° and reveal that the Oequatorial—Te—Oequatorial bonds are the most abundant linkages in the tellurite network. Two glass samples containing 7.5 and 8.5 mol.% of SrO were annealed at 350°C for 1 h to produce anti-glass phases; they were further annealed at 450°C for 4 h to transform them into crystalline phases. The anti-glass samples are disordered cubic SrTe5O11 and the disordered monoclinic SrTeO3 phases, whereas the crystalline samples contain monoclinic SrTeO3 and the orthorhombic TeO2 phases. The unit-cell parameters of the anti-glass and crystalline structures were determined by Fullprof Rietveld refinement. Thermal studies found that the glass transition temperature increases with an increase in SrO mol.% and the results on the short-range structure of glasses from Raman spectroscopy are in agreement with the RMC findings.

Rietveld refinement of X-ray powder data and bond-valence calculations of NdSrNi0.5Cr0.5O4-δ compound

2010 ◽  
Vol 25 (3) ◽  
pp. 241-246 ◽  
Author(s):  
Hanèn Chaker ◽  
Thierry Roisnel ◽  
Monica Ceretti ◽  
R. Ben Hassen
Keyword(s):  
Rietveld Method ◽  
Bond Valence ◽  
Oxygen Stoichiometry ◽  
Tetragonal Symmetry ◽  
X Ray Diffraction ◽  
Solid State Method ◽  
X Ray ◽  
Cell Parameters ◽  
Conventional Solid State Method ◽  
Bond Valence Sum

Compound from the solid-solution NdSrNi1−xCrxO4−δ, 0≤x≤1, has been prepared using conventional solid-state method and was characterized by X-ray powder diffraction. The NdSrNi0.5Cr0.5O4−δ sample shows the adoption of the K2NiF4-type structure based on the tolerance factor calculation. X-ray diffraction analysis using the Rietveld method was carried out and it was found that NdSrNi0.5Cr0.5O4−δ compound crystallizes in tetragonal symmetry with space group I4/mmm. The lattice parameters are found to be at room temperature, a=3.8012(3) Å and c=12.4812(1) Å. For X-ray diffraction data, the reliability factors are RB=0.034, Rwp=0.089, , and χ2=1.17. Bond-valence sum calculations were performed for nickel and chromium. The changes in unit-cell parameters are discussed in terms of oxygen stoichiometry and transition metal (3d) oxidation state from the perspective of the Brown bond-valence sum calculation theory.

scholarly journals High temperature structural study of decagonal Al-Cu-Rh quasicrystal.

2014 ◽  
Vol 70 (a1) ◽  
pp. C94-C94
Author(s):  
Pawel Kuczera ◽  
Walter Steurer
Keyword(s):  
Structural Changes ◽  
Configurational Entropy ◽  
Lattice Vibrations ◽  
X Ray Diffraction ◽  
Stabilization Mechanism ◽  
X Ray ◽  
Comparative Structure ◽  
The Stability

The structure of d(ecagonal)-Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals (QC) [1]. The experiments were performed at 293 K, 1223 K, 1153 K, 1083 K, and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. The results obtained for the HT structure refinements of d-Al-Cu-Rh QC seem to contradict a pure phasonic-entropy-based stabilization mechanism [2] for this QC. The trends observed for the ln func(I(T1 )/I(T2 )) vs.|k⊥ |^2 plots indicate that the best on-average quasiperiodic order exists between 1083 K and 1153 K, however, what that actually means is unclear. It could indicate towards a small phasonic contribution to entropy, but such contribution is not seen in the structure refinements. A rough estimation of the hypothetic phason instability temperature shows that it would be kinetically inaccessible and thus the phase transition to a 12 Å low T structure (at ~800 K) is most likely not phason-driven. Except for the obvious increase in the amplitude of the thermal motion, no other significant structural changes, in particular no sources of additional phason-related configurational entropy, were found. All structures are refined to very similar R-values, which proves that the quality of the refinement at each temperature is the same. This suggests, that concerning the stability factors, some QCs could be similar to other HT complex intermetallic phases. The experimental results clearly show that at least the ~4 Å structure of d-Al-Cu-Rh is a HT phase therefore entropy plays an important role in its stabilisation mechanism lowering the free energy. However, the main source of this entropy is probably not related to phason flips, but rather to lattice vibrations, occupational disorder unrelated to phason flips like split positions along the periodic axis.

Investigations of Actinide Metals and Compounds under Pressure Provide Important Insights into Bonding and Chemistry

2003 ◽  
Vol 802 ◽  
Author(s):  
R. G. Haire ◽  
S. Heathman ◽  
T. Le Bihan ◽  
A. Lindbaum ◽  
M. Iridi
Keyword(s):  
Structural Changes ◽  
Chemical Properties ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Effect Of Pressure ◽  
Electronic Configurations ◽  
5F Electrons ◽  
Actinide Series ◽  
Alloys And Compounds

ABSTRACTOne effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.

Structural changes in titanium dioxide nanocrystals during plastic deformation

2005 ◽  
Vol 38 (5) ◽  
pp. 749-756 ◽  
Author(s):  
Ulrich Gesenhues
Keyword(s):  
Structural Changes ◽  
Crystal Size ◽  
Lower Layer ◽  
High Energy ◽  
Primary Crystal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Hall Method ◽  
Means Of Transmission

The polygonization of 200 nm rutile crystals during dry ball-milling at 10gwas monitored in detail by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The TEM results showed how to modify the Williamson–Hall method for a successful evaluation of crystal size and microstrain from XRD profiles. Macrostrain development was determined from the minute shift of the most intense reflection. In addition, changes in pycnometrical density were monitored. Accordingly, the primary crystal is disintegrated during milling into a mosaic of 12–35 nm pieces where the grain boundaries induce up to 1.2% microstrain in a lower layer of 6 nm thickness. Macrostrain in the interior of the crystals rises to 0.03%. The pycnometrical density, reflecting the packing density of atoms in the grain boundary, decreases steadily by 1.1%. The results bear relevance to our understanding of plastic flow and the mechanism of phase transitions of metal oxides during high-energy milling.

The Crystal and Molecular Structures of Two Modifications of cis-Dichloro-mer-tris-(dimethylphenylphosphine)hydridoiridium(III)

1988 ◽  
Vol 41 (3) ◽  
pp. 283 ◽  
Author(s):  
GB Robertson ◽  
PA Tucker
Keyword(s):  
Heavy Atom ◽  
Molecular Structures ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Bond Lengths ◽  
Metal Ligand ◽  
Ligand Bond

The structures of two crystalline modifications of mer -(Pme2Ph)3H-cis-Cl2IrIII, (1), have been determined from single-crystal X-ray diffraction data. Modification (A) is monoclinic, space group P21/c with a 12.635(1), b 30.605(3), c 14.992(2)Ǻ, β 110.01(2)° and Z = 8. Modification (B) is orthorhombic, space group Pbca with a 27.646(3), b 11.366(1), c 17.252(2)Ǻ and Z = 8. The structures were solved by conventional heavy atom techniques and refined by full-matrix least- squares analyses to conventional R values of 0.037 [(A), 8845 independent reflections] and 0.028 [(B), 5291 independent reflections]. Important bond lengths [Ǻ] are Ir -P(trans to Cl ) 2.249(1) av. (A) and 2.234(1) (B), Ir -P(trans to PMe2Ph) 2.339(2) av. (A) and 2.344(1), 2.352(1) (B), Ir-Cl (trans to H) 2.492(2), 2.518(2) (A) and 2.503(1) (B) and Ir-Cl (trans to PMe2Ph)2.452(2) av. (A) and 2.449(1)(B). Differences in chemically equivalent metal- ligand bond lengths emphasize the importance of non-bonded contacts in determining those lengths.

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