Structure-refinement program for disordered carbons

1993 ◽  
Vol 26 (6) ◽  
pp. 827-836 ◽  
Author(s):  
H. Shi ◽  
J. N. Reimers ◽  
J. R. Dahn
Keyword(s):  
Structural Model ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Finite Size ◽  
Model Parameters ◽  
Refinement Method ◽  
The Difference ◽  
Diffraction Patterns ◽  
Optimizing Model ◽  
Average Lattice

An automated structure-refinement program has been developed for X-ray powder diffraction data collected on disordered carbons. The program minimizes the difference between the observed and calculated diffraction profiles in a least-squares sense by optimizing model parameters analogously to the popular Rietveld refinement method. Unlike the Rietveld method, which is designed for crystalline materials, this program allows the quantification of the finite size, strain and disorder present in disordered carbon fibers and cokes. For example, the structural model used includes the probability of a random translation parallel to adjacent carbon layers as a refinable parameter describing turbostratic disorder. Other parameters are used to describe finite size, fluctuations in the spacing between adjacent layers, average lattice constants, background and other important quantities. The structural model, combined with the refinement program, acceptably describes the diffraction patterns from disordered carbons such as pitch heated near 823 K, cokes, fibers, heat-treated cokes and synthetic graphite.

X-Ray Powder Diffraction Data and Crystal Refinement of a New Compound AlCrNi3Pr

2016 ◽  
Vol 850 ◽  
pp. 3-7
Author(s):  
Shu Hui Liu ◽  
Liu Qing Liang ◽  
Chang Sheng Qin ◽  
De Gui Li ◽  
Ling Min Zeng ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Structure Type ◽  
Hexagonal Structure ◽  
Powder Diffraction Data ◽  
Tungsten Electrode ◽  
X Ray ◽  
Diffraction Patterns

Rare earth-transition metal (R-T) intermetallics have been well used because of their excellent properties. The X-ray diffraction patterns of many new phases in the R-T system have not been extensively studied. A new compound AlCrNi3Pr was prepared by arc melting using non-consumable tungsten electrode under argon atmosphere, and then annealed at 1023K for 30 days. The X-ray powder diffraction data of AlCrNi3Pr was collected on a Rigaku SmartLab X-ray powder diffractometer. The powder patterns of the compound were indexed, and the structure refinement by using Rietveld method indicated that the AlCrNi3Pr compound crystallized in the hexagonal structure, space group P6/mmm (No.191) with PrNi5 structure type, a=b=5.0553(9) Ǻ, c=4.0763(6) Ǻ, V=90.22Ǻ3, Z=1, ρx=7.288g cm-3, the Smith–Snyder FOM F30=279.1(0.0044, 32) and the intensity ratio RIR=1.23.

Application of quantitative texture analysis to Rietveld profile refinement of neutron diffraction patterns of a zircaloy sample

2001 ◽  
Vol 34 (3) ◽  
pp. 358-364 ◽  
Author(s):  
Y. C. Kim ◽  
B. S. Seong ◽  
J. H. Lee ◽  
E. J. Shin
Keyword(s):  
Neutron Diffraction ◽  
Texture Analysis ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Polycrystalline Materials ◽  
Texture Information ◽  
Diffraction Patterns ◽  
The Individual ◽  
The Mathematical Model ◽  
Profile Refinement

The possibility of extending the Rietveld method to incorporate textured polycrystalline materials is demonstrated with a zircaloy sample. By assigning the pole densities obtained by separate texture analysis to the preferred orientation factors (POFs) in the mathematical model of the Rietveld method, good profile refinement results are achieved with the neutron diffraction patterns. The approach of predetermining the individual POF values from quantitative texture information can be used to improve refinement of other parameters related to the analysis of composite phases as well as to crystal structure refinement.

Reinvestigation of the Incommensurate Structure of αPbO.

2002 ◽  
Vol 755 ◽  
Author(s):  
Gianguido Baldinozzi ◽  
Jean-Marc Raulot ◽  
Vaclav Petricek
Keyword(s):  
Powder Diffraction ◽  
Structural Model ◽  
Rietveld Method ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Incommensurate Phase ◽  
Lead Monoxide ◽  
Incommensurate Structure ◽  
Diffraction Patterns ◽  
Integrated Intensities

ABSTRACTLead monoxide exists at room temperature in two forms, namely α-PbO, litharge (red, tetragonal) and β3-PbO massicot (yellow, orthorhombic). The weak bonds along the c axis and the ferroelastic nature of the incommensurate phase prevent the growth of single crystals suitable for high quality diffraction techniques (very small ferroelastic domains and frequent stacking faults in these layered structures). A structural determination of the incommensurate structure was proposed in the superspace group C2mb(0β;0) using the integrated intensities extracted from powder diffraction patterns. More recently an electron microscopy study suggested the existence of systematic extinctions affecting the satellite reflections and it supports the more symmetric space group Cmma(0β0)s. In this paper, high resolution powder diffraction patterns (synchrotron) were refined in the incommensurate phase using the Rietveld method. Various superspace groups and forms for the modulated displacements were tested. The consequences of this structural model on the electronic structure are analysed using also ab-initio calculations.

Reinvestigation of crystal structure and structural disorder of Ba3MgSi2O8

2009 ◽  
Vol 24 (3) ◽  
pp. 180-184 ◽  
Author(s):  
Tomoyuki Iwata ◽  
Tatsuya Horie ◽  
Koichiro Fukuda
Keyword(s):  
Crystal Structure ◽  
Structural Model ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Three Dimensional ◽  
Structural Disorder ◽  
Entropy Method ◽  
Reliability Indices ◽  
Distribution Maps ◽  
Atom Model

Crystal structure and structural disorder of Ba3MgSi2O8 were reinvestigated by laboratory X-ray powder diffraction. The title compound was found to be trigonal with space group P3m1, Z=1, and unit-cell dimensions a=0.561 453(4) nm, c=0.727 629(4) nm, and V=0.198 641(2) nm3. The initial structural model used for structure refinement was taken from that of glaserite (K3NaS2O8) and modified by a split-atom model. In the split-atom model, one of the two types of Ba sites and that of SiO4 tetrahedra were, respectively, positionally and orientationally disordered. The new crystal structure and structural disorder were refined by the Rietveld method. The maximum-entropy-method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The final reliability indices calculated from MPF were Rwp=6.52%, S=1.36, Rp=4.84%, RB=0.97%, and RF=0.52%. Details of the disorder structure of Ba3MgSi2O8 are shown in the three-dimensional and two-dimensional electron-density distribution maps determined by MPF.

Neutron powder diffraction data for low- and high-temperature NASICON phases of LiM2(PO4)3 (M=Hf, Sn)

1999 ◽  
Vol 14 (1) ◽  
pp. 53-60 ◽  
Author(s):  
E. Morin ◽  
T. Le Mercier ◽  
M. Quarton ◽  
E. R. Losilla ◽  
M. A. G. Aranda ◽  
...  
Keyword(s):  
High Temperature ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Powder Diffraction Data ◽  
Space Group ◽  
Neutron Powder Diffraction Data ◽  
Reversible Phase Transition ◽  
Structural Skeleton ◽  
Diffraction Patterns ◽  
Reversible Phase

The new diffraction patterns of the low- and high-temperature phases of Li0.87Hf2.032(PO4)3 and LiSn2(PO4)3 are given and indexed on the basis of a structure refinement from neutron powder data using Rietveld method. The two isotypic compounds present a reversible phase transition: triclinic (LT, space group P1¯) ⇄ rhombohedral (HT, space group R3¯c) which proceeds by topotactic distortion of the structural skeleton.

Simultaneous structure refinement of neutron, synchrotron and X-ray powder diffraction patterns

1988 ◽  
Vol 21 (1) ◽  
pp. 22-28 ◽  
Author(s):  
J. K. Maichle ◽  
J. Ihringer ◽  
W. Prandl
Keyword(s):  
Powder Diffraction ◽  
Goodness Of Fit ◽  
Structural Model ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Data Sets ◽  
Data Set ◽  
X Ray ◽  
Counting Statistics ◽  
The Individual

A technique has been developed for the simultaneous analysis of several powder diffraction data on the basis of the Rietveld method. Counting rates from one specimen at a given temperature taken at neutron, synchrotron or X-ray powder diffractometers are joined to one single data set with weights given by the counting statistics. The structure is refined from this data set with a parameter field containing one structural model and individual zero points, scale factors and FWHM parameters for each of the methods and data sets. A new definition of the residuals is given. The residuals and goodness-of-fit values are calculated for all as well as for the individual data sets.

scholarly journals To B or not to B: a question of resolution?

2012 ◽  
Vol 68 (4) ◽  
pp. 468-477 ◽  
Author(s):  
Ethan A. Merritt
Keyword(s):  
Structural Model ◽  
Structure Refinement ◽  
Atomic Displacement ◽  
Complex Model ◽  
Model Parameters ◽  
Ratio Test ◽  
Explicit Model ◽  
Medium Resolution ◽  
Factor Ratio ◽  
Atomic Displacement Parameters

In choosing and refining any crystallographic structural model, there is tension between the desire to extract the most detailed information possible and the necessity to describe no more than what is justified by the observed data. A more complex model is not necessarily a better model. Thus, it is important to validate the choice of parameters as well as validating their refined values. One recurring task is to choose the best model for describing the displacement of each atom about its mean position. At atomic resolution one has the option of devoting six model parameters (a `thermal ellipsoid') to describe the displacement of each atom. At medium resolution one typically devotes at most one model parameter per atom to describe the same thing (a `B factor'). At very low resolution one cannot justify the use of even one parameter per atom. Furthermore, this aspect of the structure may be described better by an explicit model of bulk displacements, the most common of which is the translation/libration/screw (TLS) formalism, rather than by assigning some number of parameters to each atom individually. One can sidestep this choice between atomic displacement parameters and TLS descriptions by including both treatments in the same model, but this is not always statistically justifiable. The choice of which treatment is best for a particular structure refinement at a particular resolution can be guided by general considerations of the ratio of model parameters to the number of observations and by specific statistics such as the Hamilton R-factor ratio test.

Rutile Superstructure of Sb0.9V1.1O4

1997 ◽  
Vol 53 (2) ◽  
pp. 221-230 ◽  
Author(s):  
A. R. Landa-Cánovas ◽  
S. Hansen ◽  
K. Ståhl
Keyword(s):  
Electron Diffraction ◽  
Structural Model ◽  
Rietveld Method ◽  
High Resolution Electron Microscopy ◽  
Rutile Structure ◽  
X Ray ◽  
Edge Sharing Octahedra ◽  
Resolution Electron ◽  
Diffraction Patterns ◽  
Convergent Beam

The structure of Sb0.9V1.1O4, antimony vanadium oxide, has been studied by powder X-ray diffraction, electron diffraction and high-resolution electron microscopy (HREM). The X-ray powder diffraction pattern showed only basic rutile reflections [a r = 4.6085 (1), c r = 3.0867 (1) Å] and the basic rutile structure was refined using the Rietveld method. A rutile superstructure was revealed when the sample was studied by electron diffraction. The electron diffraction patterns were indexed on the unit cell a = 21/2 a r , b = 21/2 b r , c = 2c r . Its space group, I41 md, was determined by means of convergent-beam electron diffraction (CBED). A structural model based on alternating cation ordering along c in the chains of edge-sharing octahedra is proposed and its electron diffraction patterns and HREM image are calculated and matched with the experimental ones.

X-ray powder diffraction data of potassium μ-Oxo-bis(oxodiperoxovanadate)(4-) hydrate K4[O{VO(O2)2}2]H2O

2003 ◽  
Vol 18 (3) ◽  
pp. 248-251 ◽  
Author(s):  
Maciej Grzywa ◽  
A. Rafalska-Łasocha ◽  
Wielsaw Łasocha
Keyword(s):  
Powder Diffraction ◽  
Room Temperature ◽  
Rietveld Method ◽  
Structure Refinement ◽  
Analytical Investigation ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns

The potassium μ-Oxo-bis(oxodiperoxovanadate)(4-) hydrate K4[O{VO(O2)2}2]*H2O was prepared, and its X-ray powder diffraction patterns have been recorded at room temperature. The unit cell parameters were refined to a=6.7097(1) Å, b=9.9574(1) Å, c=15.8250(3) Å, β=93.69(6)°, space group P21/c (14). The sample of K4V2O11*H2O was characterized by IR spectroscopy and analytical investigation. Results of crystal structure refinement by Rietveld method are presented; final RF and Rwp are 13 and 16%, respectively.

Fine particle preparation and electrode property of layered-type LiNi0.4Co0.6-xTixO2

2012 ◽  
Vol 1425 ◽  
Author(s):  
Kenjiro Fujimoto ◽  
Keita Ikezawa ◽  
Shigeru Ito
Keyword(s):  
Rietveld Method ◽  
Spray Deposition ◽  
Structure Refinement ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Electrostatic Spray Deposition ◽  
Air Atmosphere ◽  
Diffraction Patterns ◽  
Materials Used ◽  
Electrode Property

ABSTRACTLayered-type LiNi0.4Co0.6-xTixO2 (0≤x≤0.2) were prepared by conventional electrostatic spray deposition method for studying the correlation of crystal structure and electrode property. Starting materials used were LiNO3, Ni(NO3)2·6H2O, Co(NO3)2·6H2O and TiO2 nano-slurry. These materials were dissolved or dispersed in a mixture of ethanol and butyl carbitol and mixed by predefined ratio, respectively. Then, each of mixtures was sprayed and dried on the grounded reaction plate which was heated at 400 °C. Deposited powder was sintered at 700˚C for 10 hours in air atmosphere. Library of LiNi0.4Co0.6-xTixO2 (0≤x≤0.2) was indexed R-3m by powder X-ray diffraction patterns and its chemical compositions from ICP emission spectroscopy method corresponded to the initial composition conditions. From the diffracted intensity ratio of I(003)/I(104) and the structure refinement by Rietveld method, it was found that the proportion of cation mixing effect increased with increasing amount of Ti among of transition metals. And, from the observation by scanning electron microscope and the calculation by Scherrer’s method, the crystallite size decreased with increasing amount of Ti element. From the charge-discharge property of LiNi0.4Co0.6-xTixO2 (0≤x≤0.2) library, LiNi0.4Co0.5Ti0.1O2 showed better cycle behavior among the library.

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