scholarly journals Structure determination and crystal chemistry of large repeat mixed-layer hexaferrites

IUCrJ ◽  
2018 ◽  
Vol 5 (6) ◽  
pp. 681-698 ◽  
Author(s):  
C. Delacotte ◽  
G. F. S. Whitehead ◽  
M. J. Pitcher ◽  
C. M. Robertson ◽  
P. M. Sharp ◽  
...  
Keyword(s):  
Data Storage ◽  
Level Structure ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
Unit Cells ◽  
Atomic Coordinates ◽  
Large Repeat ◽  
Resolution Structure

Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba2Zn2Fe12O22, whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.

Unraveling the Structure of Decagonal Approximants by “Brute Force” Deconvolution of the Experimental Autocorrelation Function

2000 ◽  
Vol 643 ◽  
Author(s):  
Michael A. Estermann ◽  
Katja Lemster ◽  
Walter Steurer
Keyword(s):  
Autocorrelation Function ◽  
Diffraction Data ◽  
Brute Force ◽  
X Ray Diffraction ◽  
Large Unit ◽  
X Ray ◽  
Structure Building ◽  
Lack Of Information ◽  
Structure Solution ◽  
Unit Cells

AbstractMethods for the ab initio structure analysis of periodic approximant phases from single- crystal X-ray diffraction data are presented. These methods are particularly suited to complex approximant structures with large unit cells and strong pseudosymmetry (where routine X-ray structure solution tools fail) and are based on the “brute-force” deconvolution of the experimentally measured autocorrelation function. This function is obtained directly by a simple Fourier transform of the measured X-ray diffraction intensities. Sub-optimal diffraction data from twinned, nanodomain and polycrystalline specimens can be processed despite the inevitable lack of information due to reflection overlap and limited resolution. The deconvolution process allows complex approximant structures to be unraveled without prior knowledge about the structure-building motifs. Examples are presented for the systems Al-Co-Ni and Al-Co-(Ta).

An Approach to the Automation of a Multifunction X-Ray Diffraction Laboratory

1980 ◽  
Vol 24 ◽  
pp. 121-122
Author(s):  
T. L. Nunes
Keyword(s):  
Data Storage ◽  
Lattice Parameter ◽  
Phase Identification ◽  
X Ray Diffraction ◽  
X Ray ◽  
Program Library ◽  
Common Control ◽  
Storage Area ◽  
Technique Development ◽  
Size Estimates

A variety of x-ray diffractometers supporting stress measurements, routine phase identification, precision lattice parameter determinations, crystallite size estimates, and high temperature studies have been interfaced to a central minicomputer. The unique attributes of each instrument have been retained while the central minicomputer provides a common control format, data storage area, and analysis program library. Two movable desk top computers provide limited backup for the minicomputer, and serve as test beds for technique development.

scholarly journals High-pressure synthesis of REB5O8(OH)2 (RE = Ho, Er, Tm)

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Michael Zoller ◽  
Hubert Huppertz
Keyword(s):  
High Pressure ◽  
Rare Earth ◽  
Ir Spectroscopy ◽  
Earth Metal ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
Pressure Synthesis ◽  
The Rare Earth

AbstractThe rare earth oxoborates REB5O8(OH)2 (RE = Ho, Er, Tm) were synthesized in a Walker-type multianvil apparatus at a pressure of 2.5 GPa and a temperature of 673 K. Single-crystal X-ray diffraction data provided the basis for the structure solution and refinement. The compounds crystallize in the monoclinic space group C2 (no. 5) and are composed of a layer-like structure containing dreier and sechser rings of corner sharing [BO4]5− tetrahedra. The rare earth metal cations are coordinated between two adjacent sechser rings. Further characterization was performed utilizing IR spectroscopy.

scholarly journals Growth of sillenite Bi12FeO20 single crystals: structural, thermal, optical, photocatalytic features and first principle calculations

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Durga Sankar Vavilapalli ◽  
Ambrose A. Melvin ◽  
F. Bellarmine ◽  
Ramanjaneyulu Mannam ◽  
Srihari Velaga ◽  
...  
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Photoelectron Spectroscopy ◽  
Diffraction Method ◽  
Lattice Parameter ◽  
First Principle ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Principle Calculations ◽  
Photodegradation Efficiency

AbstractIdeal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals.

scholarly journals Measurements by x-ray diffraction of the temperature dependence of lattice parameter and crystallite size for isostatically-pressed graphite

Carbon Trends ◽  
2021 ◽  
pp. 100071
Author(s):  
Keith R. Hallam ◽  
James Edward Darnbrough ◽  
Charilaos Paraskevoulakos ◽  
Peter J. Heard ◽  
T. James Marrow ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Crystallite Size ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
X Ray

scholarly journals High-pressure synthesis and characterization of the non-centrosymmetric scandium borate ScB6O9(OH)3

2020 ◽  
Vol 75 (6-7) ◽  
pp. 597-603
Author(s):  
Birgit Fuchs ◽  
Hubert Huppertz
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Synthesis And Characterization ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Pressure High Temperature ◽  
Structure Solution ◽  
Temperature Experiment ◽  
Pressure Synthesis

AbstractThe non-centrosymmetric scandium borate ScB6O9(OH)3 was obtained through a high-pressure/high-temperature experiment at 6 GPa and 1473 K. Single-crystal X-ray diffraction revealed that the structure is isotypic to InB6O9(OH)3 containing borate triple layers separated by scandium layers. The compound crystallizes in the space group Fdd2 with the lattice parameters a = 38.935(4), b = 4.4136(4), and c = 7.6342(6) Å. Powder X-ray diffraction and vibrational spectroscopy were used to further characterize the compound and verify the proposed structure solution.

Problems Associated with Kα Doublet in Residual Stress Measurements

1979 ◽  
Vol 23 ◽  
pp. 333-339
Author(s):  
S. K. Gupta ◽  
B. D. Cullity
Keyword(s):  
Residual Stress ◽  
Silicon Powder ◽  
Lattice Parameter ◽  
Diffraction Peak ◽  
Parameter Determination ◽  
X Ray Diffraction ◽  
X Ray ◽  
Analysis Techniques ◽  
The Difference ◽  
Similar Accuracy

Since the measurement of residual stress by X-ray diffraction techniques is dependent on the difference in angle of a diffraction peak maximum when the sample is examined consecutively with its surface at two different angles to the diffracting planes, it is important that these diffraction angles be obtained precisely, preferably with an accuracy of ± 0.01 deg. 2θ. Similar accuracy is desired in precise lattice parameter determination. In such measurements, it is imperative that the diffractometer be well-aligned. It is in the context of diffractometer alignment with the aid of a silicon powder standard free of residual stress that the diffraction peak analysis techniques described here have been developed, preparatory to residual stress determinations.

scholarly journals MOVPE Growth of Quaternary (Al,Ga,In)N for UV Optoelectronics

2000 ◽  
Vol 5 (S1) ◽  
pp. 412-424
Author(s):  
Jung Han ◽  
Jeffrey J. Figiel ◽  
Gary A. Petersen ◽  
Samuel M. Myers ◽  
Mary H. Crawford ◽  
...  
Keyword(s):  
Room Temperature ◽  
Rutherford Backscattering Spectrometry ◽  
Optoelectronic Devices ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peak Energy ◽  
Movpe Growth ◽  
Pl Emission

We report the growth and characterization of quaternary AlGaInN. A combination of photoluminescence (PL), high-resolution x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) characterizations enables us to explore the contours of constant- PL peak energy and lattice parameter as functions of the quaternary compositions. The observation of room temperature PL emission at 351nm (with 20% Al and 5% In) renders initial evidence that the quaternary could be used to provide confinement for GaInN (and possibly GaN). AlGaInN/GaInN MQW heterostructures have been grown; both XRD and PL measurements suggest the possibility of incorporating this quaternary into optoelectronic devices.

scholarly journals Optimization in S-SAD phasing - difference between solved and unsolved structure

2014 ◽  
Vol 70 (a1) ◽  
pp. C613-C613
Author(s):  
Jan Stránský ◽  
Tomáš Kovaľ ◽  
Lars Østergaard ◽  
Jarmila Dušková ◽  
Tereza Skálová ◽  
...  
Keyword(s):  
Data Processing ◽  
De Novo ◽  
Protein Structures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
Sad Phasing ◽  
Optimal Values ◽  
Grant Agency ◽  
Intensity Reading

Development of X-ray diffraction technologies have made de novo phasing of protein structures by single-wavelength anomalous dispersion by sulphur (S-SAD) more common. As anomalous differences in the sulphur atomic factors are in the order of errors of measurement, careful intensity reading and data processing are crucial. S-SAD was used for de novo phasing of a small 12 kDa protein with 4 sulphur atoms per molecule at 2.3 Å, where the data did not enable a straightforward structure solution. Data processing was performed using XDS [1] and scaling using XSCALE. The sulphur substructure was determined by SHELXD [2] and phases were obtained from SHELXE [2]. Both algorithms strongly depend on input parameters and default values did not lead to the correct phases. Therefore a systematic search of optimal values of several parameters was used to find a solution. This method helped to confirm sulphur substructure and to differentiate the handedness of the solutions. Moreover, a script for comfortable conversion of SHELX outputs to MTZ format was developed, using programmes included in the CCP4 package [3]. The previously unsolvable protein structure was successfully resolved with the described procedure. This work was supported by the Grant Agency of the Czech Technical University in Prague, (SGS13/219/OHK4/3T/14), the Czech Science Foundation (P302/11/0855), project BIOCEV CZ.1.05/1.1.00/02.0109 from the ERDF.

Phase selection in precursor-derived yttrium aluminum garnet and related Al2O3–Y2O3 compositions

2005 ◽  
Vol 20 (4) ◽  
pp. 1017-1025 ◽  
Author(s):  
Ashutosh S. Gandhi ◽  
Carlos G. Levi
Keyword(s):  
Heat Treatment ◽  
Yttrium Aluminum Garnet ◽  
Lattice Parameter ◽  
Defect Structures ◽  
X Ray Diffraction ◽  
Phase Selection ◽  
X Ray ◽  
Yttrium Aluminum ◽  
Rich Side ◽  
Nitrate Solutions

Al2O3–Y2O3 powders were synthesized in the range of 25–55% Y2O3 by reverse coprecipitation of nitrate solutions. All starting powders were amorphous and formed primary yttrium aluminum garnet (YAG) upon crystallization. X-ray diffraction detected only garnet in compositions of 30–40% Y2O3 after heat treatment at 1250 °C. Compositions of 45–55% Y2O3 established a metastable YAG + Y4Al2O9 microstructure. The YAG phase field was metastably extended away from its stoichiometry, as indicated by a systematic increase in lattice parameter with Y2O3 content. Although some Al2O3 enrichment was achieved, YAG appears to tolerate greater off-stoichiometry on the Y2O3-rich side. Possible defect structures accommodating the solubility extension were examined. Phase selection results indicate that compositional inhomogeneity is not the only reason behind the appearance of hexagonal YAlO3, which is frequently reported during YAG synthesis.

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