The oxygen positional parameter in pyrochlores and its dependence on disorder

2002 ◽  
Vol 82 (1) ◽  
pp. 123-135 ◽  
Author(s):  
Licia Minervini ◽  
Robin W. Grimes ◽  
Yasunori Tabira ◽  
Ray L. Withers ◽  
Kurt E. Sickafus
Keyword(s):  
Positional Parameter

Use of Positional Parameter in Rayleigh's Method

1988 ◽  
Vol 114 (12) ◽  
pp. 2199-2203
Author(s):  
Carlos P. Filipich ◽  
Marta B. Rosales
Keyword(s):  
Positional Parameter

Novel Structure of MgSe in the Multimegabar Regime: Positional Parameter Determination

1997 ◽  
Vol 499 ◽  
Author(s):  
Arthur L. Ruoff ◽  
Ting Li ◽  
Chandrabhas Narayana ◽  
Huan Luo ◽  
Raymond G. Greene
Keyword(s):  
Equation Of State ◽  
Structural Transformations ◽  
Energy Dispersive ◽  
Parameter Determination ◽  
X Ray Diffraction ◽  
X Ray ◽  
Positional Parameter ◽  
Novel Structure ◽  
Diffraction Peaks ◽  
Intensity Calculation

ABSTRACTThe structural transformations in the II-VI compound MgSe have been studied under pressure using energy dispersive x-ray diffraction. MgSe transforms ‘continuously’ from the rocksalt (Bl) structure to a FeSi (B28) or Au-Be structure beginning at 99 ± 8 GPa. At 202 GPa, MgSe is approaching 7-fold coordination with u = 0.0828 and w = 0.4173. The method for intensity calculation of the diffraction peaks is presented. Using the Birch equation, the equation of state to 146 GPa was determined with Bo = 62.8 + 1.6 GPa and Bo′ = 4.1.

The structural parameters, structural stability and bulk modulus in RE2Sn2O7by first-principles calculations

2017 ◽  
Vol 31 (26) ◽  
pp. 1750184 ◽  
Author(s):  
C. G. Liu ◽  
J. Zhang ◽  
L. J. Chen ◽  
J. Wen ◽  
L. Y. Dong ◽  
...  
Keyword(s):  
Rare Earth ◽  
Bulk Modulus ◽  
Bond Length ◽  
Structural Stability ◽  
Density Functional ◽  
Structural Parameters ◽  
Structural Parameter ◽  
Functional Theory ◽  
Positional Parameter ◽  
Tight Connection

A systematic density functional theory study is performed to investigate the lattice parameters, the internal positional parameter [Formula: see text] and bond length of RE2Sn2O7(RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) pyrochlores. To analyze the structural stability in extreme conditions and verify whether bond strength varies inversely to bond length in rare-earth stannate pyrochlores, the structural parameter and bonding strength under hydrostatic pressure are studied. The tight connection between the different bond length contraction and the variation of 48[Formula: see text] oxygen positional parameter [Formula: see text] is also discovered. We calculated the bond length and the bulk modulus of RE2Sn2O7and found that the [Formula: see text]RE–O[Formula: see text] bond plays a predominant role in determining the bulk modulus. Meanwhile, the present calculations suggest that the “bimodal effect” also exists in rare-earth stannate pyrochlores.

XRD Based Methods of Investigation the Order - Disorder Transformation in the Spinel Structure - A Comparative Study

2013 ◽  
Vol 203-204 ◽  
pp. 129-132 ◽  
Author(s):  
Jacek Podwórny
Keyword(s):  
Spinel Structure ◽  
Cation Sublattice ◽  
Measured Temperature ◽  
Temperature Dependent ◽  
Ionic Radii ◽  
Cation Site ◽  
Cell Edge ◽  
Advantages And Disadvantages ◽  
Positional Parameter ◽  
Atomic Scattering

Three synthetic and stoichiometric 2:3 type spinels (Fd3m symmetry): MgAl2O4, MgFe2O4, NiAl2O4 with a different initial structural order in cation sublattice were investigated. Investigations by means of high temperature XRPD method at temperatures ranging from 25°C to 1100°C were carried out. Diffraction patterns at each temperature in isothermal conditions were measured. For each tested spinel changes in several temperature-dependent parameters were measured: oxygen positional parameter u(T), cell edge a0(T), cation site occupancies Occ(T) in tetrahedral and octahedral positions and a cation-anion distance in tetrahedral TO(T) and octahedral MO(T) positions. Temperatures of initial order-disorder transformation were determined on the basis of the course of these dependences. Basing on changes of the cell edge a0(T), the values of thermal expansion coefficient and for spinel before and after the beginning of order-disorder transformation, respectively, were calculated. The values of measured temperature-dependent parameters were used to calculate the degree of inversion x in the spinel structure defined as the number of 3+ cations in tetrahedral sites. In each case two methods of calculating the degree of inversion from experimental data were applied. The first method involved observing the changes in sites occupancy in the cation sublattice versus temperature, which resulted in a change of diffraction lines intensities. The second method was based on observing the changes in cation-anion distances in tetra- and octahedral coordination versus temperature. The results obtained by both methods were compared, discussed and advantages and disadvantages of each of them were presented. It was shown that when atomic scattering factors of cations 2+ and 3+ in the spinel structure differ significantly, the most precise method is the one based on changes in sites occupancies versus temperature. The method based on calculation of changes in cation-anion distances is recommended when atomic scattering factors of cations differ slightly but oxygen positional parameter and cation-anion distances changes significantly during order-disorder transformation like in normal spinel structure when effective ionic radii of 2+ and 3+ cations differ significantly.

Detection of ZAP70 Negative B-CLL Patients Using the Beckman Coulters Positional Parameter Technology and RPD (Research Population Data) Analysis.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 4934-4934
Author(s):  
Varda Deutsch ◽  
Yair Herishanu ◽  
Aaron Polliack ◽  
Elizabeth Naparstek ◽  
Dina Meyuhas ◽  
...  
Keyword(s):  
Protein Tyrosine Kinase ◽  
Population Data ◽  
Good Prognosis ◽  
Receiver Operating Curve ◽  
Control Group ◽  
Hematological Disorders ◽  
Volume Conductivity ◽  
Aggressive Disease ◽  
Positional Parameter ◽  
Receiver Operating Curve Analysis

Abstract B-CLL, the most common type of leukemia in adults, is heterogeneous with a varying clinical course ranging from indolent to aggressive disease. CLL patients with mutated Ig V(H) genes have a good prognosis while those with non-mutated Ig V(H) status and expression of the ZAP70 protein tyrosine kinase generally have aggressive disease and shorter survival. Testing for IgV(H) mutations is not routinely performed due to cost and ZAP70 testing is still technically difficult. As these tests remain generally inappropriate for B-CLL patient screening, we tested the capacity of the new Beckmann Coulter LH750 blood analyzers to provide additional morphometric information on the CLL cell population. These analyzers use a highly informative positional parameter technology - VCS (Volume, Conductivity, Scatter) technology, and automated RPD analysis which provide the Mean and Standard Deviation of Volume, Conductivity and Scatter (VCS) for each of the main WBC types (neutrophils, lymphocytes, monocytes and eosinophils), thereby enabling the detection of abnormal WBC populations associated with various hematological and non-hematological disorders. We attempted to determine if the RPD generated could differentiate between the ZAP70pos and ZAP70neg B-CLL subgroups as determined by high resolution quantitative ZAP70 flow cytometry analysis (1). This study included 30 newly diagnosed untreated CLL patients. CBC was performed on all samples using automated leukocyte differentials in the Beckmann-Coulter LH750. Statistical analysis was performed with Medcalc® 8.1.1.0. Results show that there was no correlation between the WBC number, ZAP70pos expression (found in 59% of the cases) and lymphocyte volume, scatter, or conductivity or SD of these parameters. However, differences in the automated morphology of the Zap70neg compared with Zap70pos CLL lymphocytes was detected. When compared to normal lymphocyte volume (85.8±14.5), the Lymphocyte Mean Volume (MLYV) was lower in the ZAP70neg samples (77.7±17.6) (p<0.05), while the ZAP70pos samples had increased volumes (87.5±15.8), similar to values reported in other myeloproliferative states. The conductivity of the ZAP70neg cells was reduced (110±15.0) below normal (117±11.5) (p=0.038), while the ZAP70pos cells had conductivity similar to the control group. Higher levels of lymphocyte apoptosis were clearly observed in the ZAP70neg samples by VCS. When using ROC (receiver operating curve analysis) to detect the potential ZAP70neg cases, the cut off proposed is MLYV < 76 with a sensitivity of 69.2% and a specificity of 70% AUC 0,650. Herein we propose an entirely new approach which may provide a novel diagnostic screening approach to enable identification of CLL patients who do not require further complex testing. This data is derived directly from the CBC of the Beckman-Coulter LH750 analyzers at no extra cost. As it will be necessary to analyze many more cases from different laboratories, an international working group has been formed in an attempt to confirm these early observations.

Variation of the oxygen positional parameter in pyrochlores.

1969 ◽  
Vol 8 (9) ◽  
pp. 2039-2039 ◽  
Author(s):  
Henry R. Hoekstra ◽  
Stanley Siegel
Keyword(s):  
Positional Parameter
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