Two computer programs for the automatic analysis of powder diffraction patterns

1995 ◽  
Vol 28 (5) ◽  
pp. 646-649 ◽  
Author(s):  
S. M. Clark
Keyword(s):  
Phase Transition ◽  
Ammonium Chloride ◽  
Powder Diffraction ◽  
Kinetic Studies ◽  
Tricalcium Silicate ◽  
Automatic Analysis ◽  
Powder Pattern ◽  
Large Numbers ◽  
Diffraction Peaks ◽  
Diffraction Patterns

Two programs for the automatic analysis of large numbers of powder diffraction patterns have been developed. The first, PEAKFIT, fits functions describing the diffraction peaks and baseline to single or multiple peaks in a number of predefined regions of each powder pattern. The second, FULFIT, fits the entire powder pattern with a combination of functions describing the diffraction peaks and background. The use of these programs is illustrated with data analysed as part of kinetic studies of the I–II phase transition in ammonium chloride and the hydration of tricalcium silicate.

High-temperature structural evolution of hexagonal multiferroic YMnO3and YbMnO3

2007 ◽  
Vol 40 (4) ◽  
pp. 730-734 ◽  
Author(s):  
Il-Kyoung Jeong ◽  
N. Hur ◽  
Th. Proffen
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Structural Parameters ◽  
Structural Evolution ◽  
Neutron Powder Diffraction ◽  
Temperature Behaviour ◽  
Rietveld Refinements ◽  
Polar Structure ◽  
Diffraction Patterns

Neutron powder diffraction studies on the structural evolution of hexagonal multiferroic YMnO3and YbMnO3from 1000 K to 1400 K, and from 1000 K to 1350 K, respectively, are presented. The temperature evolution of diffraction patterns suggests that YMnO3undergoes a phase transition to a non-polar structure above 1200 K, while YbMnO3remains ferroelectric up to 1350 K. Detailed structural parameters were obtained as a function of temperature from Rietveld refinements. Based on this result, the distinct differences in temperature behaviour between YMnO3and YbMnO3, and the origin of the ferroelectricity in these hexagonal multiferroics are discussed.

Indexing Powder Patterns from Relative Axial Dimensions

1990 ◽  
Vol 5 (2) ◽  
pp. 61-63
Author(s):  
Ben Post ◽  
W. Frank McClune
Keyword(s):  
Data Base ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Single Phase ◽  
Unit Cell ◽  
X Ray ◽  
Large Numbers ◽  
Diffraction Patterns ◽  
Goniometric Measurements ◽  
The One

The usefulness of an X-ray powder diffraction data base, such as the one published by the International Centre for Diffraction Data, is largely dependent on continued additions of indexed powder patterns of single-phase materials of interest to data-base users. The single-phase character of a specimen is generally established by using known values of the unit cell constants to index all its powder pattern lines.In this manuscript we describe indexing procedures based on crystal data which provide only relative values of the cell dimensions, rather than the absolute values usually considered to be essential to the indexing process. To the best of our knowledge, the use of such data for indexing powder diffraction patterns has generally been overlooked or ignored by X-ray crystallographers. We refer to the large numbers of goniometric measurements of crystals which have been published both before, and since, the discovery of X-ray diffraction. These provide useful descriptions of chemical and physical properties of crystals as well as measurements of relative dimensions of unit cell axes. The latter are presented in the form of a/b, b/b and c/b, together with the interaxial angle or angles, if the cell is nonorthogonal.

Barium hollandite-type compounds BaxFe2xTi8−2xO16 with x=1.143 and 1.333

1999 ◽  
Vol 14 (1) ◽  
pp. 31-35 ◽  
Author(s):  
J. M. Loezos ◽  
T. A. Vanderah ◽  
A. R. Drews
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Powder Diffraction ◽  
Framework Structure ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Acta Crystallogr

Experimental X-ray powder diffraction patterns and refined unit cell parameters for two barium hollandite-type compounds, BaxFe2xTi8−2xO16, with x=1.143 and 1.333, are reported here. Compared to the tetragonal parent structure, both compounds exhibit monoclinic distortions that increase with Ba content [Ba1.333Fe2.666Ti5.334O16: a=10.2328(8), b=2.9777(4), c=9.899(1) Å, β=91.04(1)°, V=301.58(5) Å3, Z=1, ρcalc=4.64 g/cc; Ba1.143Fe2.286Ti5.714O16: a=10.1066(6), b=2.9690(3), c=10.064(2) Å, β=90.077(6)°, V=301.98(4) Å3, Z=1, ρcalc=4.48 g/cc]. The X-ray powder patterns for both phases contain a number of broad, weak superlattice peaks attributed to ordering of the Ba2+ ions within the tunnels of the hollandite framework structure. According to the criteria developed by Cheary and Squadrito [Acta Crystallogr. B 45, 205 (1989)], the observed positions of the (0k1)/(1k0) superlattice peaks are consistent with the nominal x-values of both compounds, and the k values calculated from the corresponding d-spacings suggest that the Ba ordering within the tunnels is commensurate for x=1.333 and incommensurate for x=1.143. High-temperature X-ray diffraction data indicate that the x=1.333 compound undergoes a monoclinic→tetragonal phase transition between 310 and 360 °C.

Sorbate Rearrangement and Cation Migration in HFC-134 Loaded NaY Zeolite: a Temperature Dependent Synchrotron Powder Diffraction Study

2004 ◽  
Vol 443-444 ◽  
pp. 295-298
Author(s):  
A.F. Gualtieri ◽  
P. Norby ◽  
C. P. Grey ◽  
J.C. Hanson
Keyword(s):  
Phase Transition ◽  
Powder Diffraction ◽  
Unit Cell ◽  
Imaging Plate ◽  
Time Data ◽  
Temperature Dependent ◽  
Synchrotron Powder Diffraction ◽  
Cation Migration ◽  
Diffraction Patterns ◽  
Using Data

The HFC-134/NaY binding has been monitored by temperature dependent X-ray powder diffraction. Diffraction patterns were obtained as a function of different loading levels to investigate the rearrangement of the cations and of the HFC-134 molecules, in the temperature range 100-230 K. In situ real-time data were collected using a Translating Imaging Plate System (TIPS) at the NSLS (USA). Rietveld structure refinements were performed for the HFC-134 (32 molecules per unit cell [m/uc = molecules per unit cell] or 4 molecules per supercage [m/sc = molecules per supercage]) using data collected from 100 to 230 K. A phase transition is observed at about 180 K (A to B phase transition) where a disordering of the HFC-134 molecule takes place and modification of its surrounding due to Na+migrations is observed. These results are preliminary and the experiment with the 32 m/uc should be repeated in order to assess whether the observed effect is reproducible.

Synthesis of cerium oxide (CeO2) by co-precipitation for application as a reference material for X-ray powder diffraction peak widths

2018 ◽  
Vol 33 (1) ◽  
pp. 21-25 ◽  
Author(s):  
Anderson Márcio de Lima Batista ◽  
Marcus Aurélio Ribeiro Miranda ◽  
Fátima Itana Chaves Custódio Martins ◽  
Cássio Morilla Santos ◽  
José Marcos Sasaki
Keyword(s):  
Powder Diffraction ◽  
Function Analysis ◽  
Diffraction Peak ◽  
Debye Function ◽  
Fourier Decomposition ◽  
Diffraction Peaks ◽  
Diffraction Patterns ◽  
Pattern Modeling ◽  
Co Precipitation ◽  
Peak Widths

Several methods can be used to obtain, from powder diffraction patterns, crystallite size and lattice strain of polycrystalline samples. Some examples are the Scherrer equation, Williamson–Hall plots, Warren/Averbach Fourier decomposition, Whole Powder Pattern Modeling, and Debye function analysis. To apply some of these methods, it is necessary to remove the contribution of the instrument to the widths of the diffraction peaks. Nowadays, one of the main samples used for this purpose is the LaB6 SRM660b commercialized by the National Institute of Standard Technology; the width of the diffraction peak of this sample is caused only by the instrumental apparatus. However, this sample can be expensive for researchers in developing countries. In this work, the authors present a simple route to obtain micron-sized polycrystalline CeO2 that have a full width at half maximum comparable with the SRM660b and therefore it can be used to remove instrumental broadening.

scholarly journals Determination of the activation energies of phase transition for calcium orthophosphates based on powder X-ray diffraction data

2021 ◽  
Author(s):  
Kateryna Vasylenko ◽  
Yuriy Sakhno ◽  
Deb Jaisi ◽  
Mykola Nikolenko
Keyword(s):  
Phase Transition ◽  
Activation Energy ◽  
Calcium Phosphate ◽  
Powder Diffraction ◽  
Early Stage ◽  
Degree Of Crystallinity ◽  
Calcium Orthophosphate ◽  
X Ray ◽  
Calcium Orthophosphates ◽  
Diffraction Peaks

Abstract Kinetic studies of the transformation of calcium orthophosphates metastable precipitates were performed under different synthesis conditions. Phase composition and degree of crystallinity were investigated by X-ray powder diffraction analysis. In acidic solution, precipitates of CaHPO4⋅2H2O (DCPD) and CaHPO4 (DCPA) are formed at the early stage of precipitation, with the degree of crystallinity at the range of 17–35%. Specifically, DCPD precipitates at 30°C and anhydrous DCPA at 50°C. In alkaline solution (pH 8–10), only amorphous forms of calcium orthophosphate is precipitated, which is explained by the high degree of supersaturation (i.e., the high rate of precipitation compared to that in acidic media). The diffraction peaks of DCPD and DCPA are found to be 0.3–0.45 degrees lower relative to their reference data, which is caused by decrease of lattice strain during early stage of crystallization. Furthermore, the initial molar ratio of Ca/P in reagent mixture was found to play subordinary role in determining the composition of final calcium phosphate precipitates. The effect of pH on the composition of precipitates is illustrated by the solubility isotherms of pure calcium orthophosphates. Given that the intensities of diffraction peaks are proportional to planar density of the material in the given plane, we propose, for the first time, to determine activation energy of phase transformation of calcium orthophosphate from X-ray powder diffraction patterns. Based on this relationship developed, the activation energy for the recrystallization DCPD and DCPA are 10.2 and 13.1 kJ/mol, respectively and for the phase transition of DCPD to DCPA – 36.7 kJ/mol. Further recrystallization to most thermodynamically stable Ca10(PO4)6(OН)2 hydroxyapatite (HA) occurs at the activation energy of 5.2 kJ/mol. These findings are critical on phase transition and transformation of calcium phosphate minerals.

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