scholarly journals Synthesis and structural characterization of Ca12Ga14O33

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Sabrina E. A. McCoy ◽  
John R. Salasin ◽  
S. Michelle Everett ◽  
Claudia J. Rawn
Keyword(s):  
Powder Diffraction ◽  
Structural Model ◽  
Electronic Band Structure ◽  
Rietveld Method ◽  
Experimental Studies ◽  
Phase Evolution ◽  
Neutron Powder Diffraction ◽  
Electronic Band ◽  
Wet Chemistry ◽  
X Ray

Abstract Ca12Ga14O33 was successfully synthesized using a wet chemistry technique to promote the homogenous mixing of the Ca and Ga cations. Rietveld refinements on X-ray and neutron powder diffraction data confirm that the compound is isostructural to Ca12Al14O33, however, with a significantly larger lattice parameter allowing for the cages that result from the framework arrangement to expand. In naturally occurring Ca12Al14O33, the mineral mayenite, these cages are occupied by O2− anions, however, experimental studies exchanging the O2− anions with other anions has led to a host of applications, depending on the caged anion. The functional nature of the structure, where framework distortions coupled with cage occupants, are correlated to electronic band structure and modifications to the framework could lead to interesting physical properties. The phase evolution was tracked using thermogravimetric analysis and high temperature X-ray diffraction and showed a lower formation temperature for the Ca12Ga14O33 analogue compared to Ca12Al14O33 synthesized using the same wet chemistry technique. Analyzing both X-ray and neutron powder diffraction using the Rietveld method with two different starting models results in one structural model, with one Ca position and the caged O on a 24d special position, being preferred.

Polymorphism of Ba1–xSrxCoO3–δ (0≤ x≤ 1) Perovskites: A Thermal and Structural Study by Neutron Diffraction

2008 ◽  
Vol 63 (6) ◽  
pp. 647-654 ◽  
Author(s):  
Cristina de la Calle ◽  
José Antonio Alonso ◽  
Maria Teresa Fernández-Díaz
Keyword(s):  
Solid Solution ◽  
Powder Diffraction ◽  
Rietveld Method ◽  
Structural Evolution ◽  
Neutron Powder Diffraction ◽  
Slow Cooling ◽  
X Ray ◽  
High Oxygen Pressure ◽  
Hexagonal Perovskites ◽  
Citrate Precursors

The preparation of different hexagonal, orthorhombic and cubic polymorphs of the solid solution Ba1−xSrxCoO3−δ (0 ≤ x ≤ 1) is described. The samples have been studied by thermal analysis (TG and DTA) to identify the phase transitions; the thermal structural evolution and the structural characterization of different phases were analyzed by X-ray and neutron powder diffraction and refined by the Rietveld method. A series of hexagonal perovskites Ba1−xSrxCoO3−δ (0 ≤ x < 0.5), labelled as “H”, were synthesized by thermal treatment of reactive citrate precursors at 900 °C in high oxygen pressure followed by slow cooling to r. t. The hexagonal perovskites with 0.5 ≤ x ≤ 1 were obtained from the citrate precursors heated twice at 900 °C in air and slowly cooled in the furnace. Orthorhombic brownmillerite-like structures, labelled “O”, were obtained from precursors with composition 0.5 ≤ x ≤ 1 by quenching in liquid N2 from 900 °C. For x < 0.5, quenching from high temperatures does not stabilize the “O” phases. The crystal structure for both terms of the solid solution (x = 0 and x = 1) has been investigated by neutron powder diffraction. DTA and X-ray thermo-diffractometry show that “H” phases experience a reconstructive transition at ca. 900 °C to give cubic “C” polymorphs.

scholarly journals The Rietveld Method ? A Historical Perspective

1988 ◽  
Vol 41 (2) ◽  
pp. 113 ◽  
Author(s):  
HM Rietveld
Keyword(s):  
Powder Diffraction ◽  
Historical Perspective ◽  
Rietveld Method ◽  
Neutron Powder Diffraction ◽  
X Ray Diffraction ◽  
Small Step ◽  
Elastic Neutron ◽  
X Ray ◽  
Measured Profile ◽  
Integrated Intensities

differences between observed and calculated values was already well established in crystallography. From there it was, in retrospect, only a small step to refrain from using the integrated intensities as observed values but to use the actual measured profile intensities obtained by step scanning the powder diagram. The Rietveld method was first reported at the I.U.Cr. congress in Moscow in 1966. However, it was not until 1975, when it was also applied to X-ray diffraction, that it became widely accepted. Nowadays its use is no longer confined to elastic neutron powder diffraction, but to all diffraction techniques producing complex diffraction diagrams.

scholarly journals Electron Diffraction vs aperiodic crystal: from indexation to structure solution

2014 ◽  
Vol 70 (a1) ◽  
pp. C1194-C1194
Author(s):  
Philippe Boullay ◽  
Gwladys Mouillard ◽  
Nicolas Barrier ◽  
Olivier Perez ◽  
Lukas Palatinus
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
Structural Model ◽  
Neutron Powder Diffraction ◽  
Accurate Estimation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
The Difference ◽  
Aperiodic Crystals

Can we solve aperiodic structures using intensities from electron diffraction? Yes! How? No mystery about it: the data analysis and the tools used for structure solution are essentially the same as the ones used in X-ray crystallography. The trick actually lies in new approaches used in electron crystallography. In analogy to X-ray diffraction, the so-called Electron Diffraction Tomography (EDT) [1] corresponds to a phi-scan data collection on a single crystal. There lies one major advantage of this technique: a powder sample is easily converted to infinitely large number of single crystals for electron diffraction. In case of aperiodic crystals this makes the difference over X-ray or neutron powder diffraction where, often, the lack of peaks clearly assignable to satellite reflections prevents any indexation and further analysis of the structure [2]. EDT allows for an accurate estimation of the modulation vector and a good guess of the super space group. These informations can be advantageously used as an input for X-ray or neutron powder diffraction. Not limited to indexation, EDT combined with Precession Electron Diffraction (PED) [3], offers a unique tool for solving modulated structures when crystals suitable for X-ray diffraction are missing. By limiting the paths for multiple scattering, PED makes the diffracted intensities closer to kinematical approximation so that they can be used efficiently for structure solution. Regarding aperiodic crystals, the superspace electron density map, generated as an output of the charge flipping algorithm used in Superflip, can be interpreted to obtain a structural model. This will be illustrated on a series of layered materials closely related to the Aurivillius phases belonging to the pseudo-binary Bi5Nb3O15-ABi2Nb2O9 (A=Pb, Sr, Ca, Ba). Limitations and possible combination with powder diffraction patterns will be discussed.

ChemInform Abstract: Synchrotron X-Ray Powder Diffraction and Electronic Band Structure of α- and β-Cu2ZnSiS4.

ChemInform ◽  
2013 ◽  
Vol 44 (11) ◽  
pp. no-no
Author(s):  
Kimberly A. Rosmus ◽  
Carl D. Brunetta ◽  
Matthew N. Srnec ◽  
Balamurugan Karuppannan ◽  
Jennifer A. Aitken
Keyword(s):  
Band Structure ◽  
Powder Diffraction ◽  
Electronic Band Structure ◽  
Electronic Band ◽  
X Ray

Structure of LaNi3.8AlMn0.2 Compounds Studied by Neutron Powder Diffraction

2016 ◽  
Vol 847 ◽  
pp. 26-28
Author(s):  
Wen Ze Han ◽  
Hao Guo ◽  
Kai Sun ◽  
De Min Chen ◽  
Shi Liu ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Annealing Temperature ◽  
Rietveld Method ◽  
Neutron Powder Diffraction ◽  
Lattice Parameters ◽  
Linear Variation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Space Groups

The structures of as-cast LaNi3.8AlMn0.2 alloys and subsequent compounds by means of annealing at different temperature (850, 900, 950, 1000 oC) were examined by using neutron powder diffraction (NPD) and X-ray diffraction (XRD). Based on the Rietveld method, the diffraction data was refined using FullProf software. The refined results demonstrate the structure types of all compounds are CaCu5 type and their space groups are P6/mmm. Increasing the annealing temperature, the lattice parameters of LaNi3.8AlMn0.2 compounds did not possess clearly linear variation. It is noted that Mn atoms do not occupy the 2c sites but occupy the 3g sites in all compounds.

Synchrotron X-ray Powder Diffraction and Electronic Band Structure of α- and β-Cu2ZnSiS4

2012 ◽  
Vol 638 (15) ◽  
pp. 2578-2584 ◽  
Author(s):  
Kimberly A. Rosmus ◽  
Carl D. Brunetta ◽  
Matthew N. Srnec ◽  
Balamurugan Karuppannan ◽  
Jennifer A. Aitken
Keyword(s):  
Band Structure ◽  
Powder Diffraction ◽  
Electronic Band Structure ◽  
Electronic Band ◽  
X Ray

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.

The structure of two manganese hexacyanometallates(II): Mn2[Fe(CN)6].8H2O and Mn2[Os(CN)6].8H2O

2002 ◽  
Vol 17 (2) ◽  
pp. 144-148 ◽  
Author(s):  
A. Gómez ◽  
V. H. Lara ◽  
P. Bosch ◽  
E. Reguera
Keyword(s):  
Crystal Structures ◽  
Coordination Sphere ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structural Model ◽  
Rietveld Method ◽  
Monoclinic Space Group ◽  
Powder Diffraction Data ◽  
Crystallization Water ◽  
X Ray

The crystal structures of two manganese hexacyanometallates(II), Mn2[Fe(CN)6].8H2O and Mn2[Os(CN)6].8H2O, were refined from X-ray powder diffraction data using the Rietveld method, with the reported structure for Mn2[Ru(CN)6].8H2O used as a structural model. These compounds are isomorphous and crystallize in the monoclinic space group P21/n. Their crystallization water is not firmly bound and can be removed without disrupting the M–C≡N–Mn network. In the dehydrated complexes, the outer cation (Mn) remains linked to only three N atoms from CN ligands while the inner cation (Fe,Os) preserves its coordination sphere. The IR, Raman, and Mössbauer spectra for the hydrated and anhydrous forms are explained based on the refined structures.

Determination and Rietveld refinement of the crystal structure of Li0.50Ni0.25TiO(PO4) from powder X-ray and neutron diffraction

2002 ◽  
Vol 17 (4) ◽  
pp. 290-294 ◽  
Author(s):  
B. Manoun ◽  
A. El Jazouli ◽  
P. Gravereau ◽  
J. P. Chaminade ◽  
F. Bouree
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Neutron Powder Diffraction ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Neutron Powder Diffraction Data ◽  
Monoclinic Cell

The structure of the oxyphosphate Li0.50Ni0.25TiO(PO4) has been determined from conventional X-ray and neutron powder diffraction data. The parameters of the monoclinic cell (space group P21/c, Z=4), obtained from X-ray results, are: a=6.3954(6) Å, b=7.2599(6) Å, c=7.3700(5) Å, and β=90.266(6)°; those resulting from neutron study are: a=6.3906(7) Å, b=7.2568(7) Å, c=7.3673(9) Å, and β=90.234(7)°. Refinement by the Rietveld method using whole profile, leads to satisfactory reliability factors: cRwp=0.128, cRp=0.100, and RB=0.038 for X-ray and cRwp=0.110, cRp=0.120, and RB=0.060 for neutrons. The structure of Li0.50Ni0.25TiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing TiO6 octahedra running parallel to the c axis and cross linked by phosphate tetrahedra. In this framework, there are octahedral cavities occupied by Li and Ni atoms: Li occupies the totality of the 2a sites and Ni occupies statistically half of the 2b sites. Ti atoms are displaced from the center of octahedra units in alternating long (2.242 Å) and short (1.711 Å) Ti–O bonds along chains.

Sign in / Sign up

Export Citation Format

Share Document