The determination of unit-cell parameters from a Laue diffraction pattern

Carr, Pamela; Dodd, I. M.; Harding, Marjorie M.

doi:10.1107/s0021889892012391

Cited by 11 publications

(8 citation statements)

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“…The unitcell dimensions are not normally derivable from a Laue diffraction pattern. The axial ratios and angles can be derived (Carr, Cruickshank & Harding, 1992) and the cell dimensions can be determined if the minimum wavelength present in the incident synchrotron radiation beam is known exactly (Carr, Dodd & Harding, 1993).…”

Section: The Laue Methodsmentioning

confidence: 99%

Recording Diffraction Data for Structure Determination for Very Small Crystals

Harding¹

1996

J Synchrotron Rad

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An account is given of experiences in recording diffraction data with synchrotron radiation to determine structures for very small crystals, too small for use with conventional X-ray sources and diffractometers. The effect of crystal composition as well as size on the relative intensity of diffraction patterns of different crystals is noted. Crystal mounting is briefly described. Experimental methods are outlined including detectors and other instrumentation, and a range of examples is given; these include the use of both monochromatic area-detector systems for intensity measurement and of the white-beam Laue method. Choice of the shortest wavelength available with adequate intensity is recommended. The examples include organic, organometallic and aluminophosphate compounds; in all cases structure determination was important in relation to chemical research projects -they were not chosen as 'test' crystals. Comparison is made of the quality of the structure refinements achieved with those from synchrotron radiation powder diffraction -the alternative method when good-sized crystals are not available. Commonly it is found that when good-quality large crystals of a substance cannot be grown, the small crystals are poor in quality with substantial mosaic spread; the relationship between mosaic spread, structure, morphology and crystal growth is explored.

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Section: The Laue Methodsmentioning

confidence: 99%

Recording Diffraction Data for Structure Determination for Very Small Crystals

Harding¹

1996

J Synchrotron Rad

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“…palladium, 0.1 mm, to make the minimum wavelength present a sharp and identifiable limit (Carr, Dodd & Harding, 1993). Without this experimental information the absolute scale can still be estimated to within 10-20%, using the known characteristics of the beamline, and this may be sufficient to identify the crystal.…”

Section: Determination Of the Unit Ceil On An Absolute Scalementioning

confidence: 99%

Application of Synchrotron Radiation Laue Diffraction to Small Single Crystals of a Mineral – Structure Determination and Identification

Kariuki¹,

Harding²

1995

J Synchrotron Radiat

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The potential of synchrotron radiation Lane diffraction pattems for structure determination and for identification of small single crystallites is illustrated. Diffraction pattems were recorded for several crystallites, _<20 l.tm in all dimensions, with the intention of determining an unknown mineral structure. They were the largest particles in the sample. They appeared to represent at least two different phases, but eventually it became clear that neither corresponded to the unknown phase. However, it has been possible to show that both identification and structure determination are practicable from Laue diffraction patterns of crystallites of this size. For one crystallite the diffraction patterns were used to derive unit-cell dimensions and from these the crystallite could be identified as either PbCO3, cerussite, or SrCO3, strontianite. Using intensity measurements it could be shown to be PbCO3. Identification could be similarly achieved for many other small single crystallites, and the procedure is described. For another crystallite, a complete structure determination was carded out and it was then recognized as malachite, Cu2(OH)2CO3. The structure found is in very good agreement with that previously determined by Zigan,

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“…A modern adaptation resembling the Braggs' method was described by Carr, Dodd & Harding (1993) and Carr, Cruickshank & Harding (1992), who define A,,lin by inserting a metal foil into an incident 'white' beam from a synchrotron. The foil provides a sharp cutoff in the highenergy portion of the X-ray spectrum.…”

confidence: 99%

“…Using solely Laue data it is difficult to determine unit-cell dimensions accurately (Ravelli, Hezemans, Krabbendam & Kroon, 1996;Carr, Dodd & Harding, 1993;Carr, Cruickshank & Harding, 1992) and much information is hidden in the 10-20% of spots containing harmonic overlap (Cruickshank, Helliwell & Moffat, 1987). The multiple Laue spots contain information useful for the assignment of space groups (Amoros, Buerger & Canut de Amoros, 1975).…”

Section: Introductionmentioning

confidence: 99%

Application of Energy-Resolved Measurements to Laue Diffraction: Determination of Unit-Cell Parameters, Deconvolution of Harmonics and Assignment of Systematic Absences

Hanley¹,

Campbell²,

Denton³

1997

J Synchrotron Radiat

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The use of energy-resolved area detection of Laue diffraction patterns for the determination of unitcell parameters and systematic absences is demonstrated. Seven different crystals having previously known unit cells were re-examined using Laue diffraction methods. These crystals included four different crystal systems including cubic, orthorhombic, tetragonal and monoclinic cells. The crystals had cell sizes ranging from 179.4 to 4588.3 A~. Comparison of known and re-determined cells showed good agreement (ratio of known to measured cells = 0.987 _+ 0.18). A single procedure was suitable for all unit-cell determinations. The accuracy of the method is presently limited by the quality of the available energy measurements. Some of the crystals represent space groups containing systematic absences normally obscured by harmonic overlap when using the Laue method. These include absences due to 21 screw axes (h, k or 1 = 2n + 1) and cell centering (h + k = 2n + 1). All systematic absences were identified using a combination of multiple linear regression with either stepwise elimination or stepwise inclusion and an F test for assignment of systematic absence. The methods are discussed in detail and simulations are used to evaluate critical tolerances for future systems.

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The determination of unit-cell parameters from a Laue diffraction pattern

Cited by 11 publications

References 1 publication

Recording Diffraction Data for Structure Determination for Very Small Crystals

Recording Diffraction Data for Structure Determination for Very Small Crystals

Application of Synchrotron Radiation Laue Diffraction to Small Single Crystals of a Mineral – Structure Determination and Identification

Application of Energy-Resolved Measurements to Laue Diffraction: Determination of Unit-Cell Parameters, Deconvolution of Harmonics and Assignment of Systematic Absences

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