Diffuse X-ray scattering and strain effects in disordered crystals

Welberry, T. R.

doi:10.1107/s0108767300016822

Cited by 25 publications

(17 citation statements)

References 16 publications

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“…The only limitation is the extent to which the MC energy can be made to realistically represent the real system energy. At one extreme a very simplified model may be useful in demonstrating particular qualitative effects 12 while at the other a quantitative and very detailed description of a disordered structure can be obtained. 13 In previous work 9 a fairly simplistic and rather artificial approach was taken in order to demonstrate a number of key effects that give rise to distinctive features in the diffuse scattering data of PZN.…”

Section: Introductionmentioning

confidence: 99%

Chemical origin of nanoscale polar domains inPbZn1∕3Nb2∕3O3

2006

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We describe the development of an atom-based Monte Carlo simulation model which gives rise to a nanoscale polar domain structure as envisaged to occur in Pb͑Zn 1/3 Nb 2/3 ͒O 3 ͑PZN͒ and similar relaxor ferroelectric materials. Individual domains are essentially thin platelike domains normal to each of the six ͗110͘ directions. Calculated diffuse scattering patterns have been obtained from the simulations, and these are in good agreement with observed neutron scattering data. Nanoscale domain formation is driven by the need for the Pb atoms to satisfy their valence requirements; within a planar domain, the Pb atoms are displaced in a concerted fashion away from the center of their 12-fold coordination polyhedra with an in-plane displacement along ͗110͘ towards one of the coordinating O atoms. The B-site cations Zn and Nb display a strong tendency to alternate in the ͗100͘ directions but complete order is frustrated by the 2:1 stoichiometry. No diffraction evidence has been found that this B-site ordering is directly linked to the nanoscale polar domain ordering. Such a linkage cannot be completely ruled out, but if it does exist, its effect on the diffraction pattern must be quite subtle. The B-site ordering does play an indirect role in establishing the average cell dimension, which in turn dictates the magnitude of the Pb displacements. The effect of applying an external electric field is modeled, and the results are found to be consistent with experiment.

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Section: Introductionmentioning

confidence: 99%

Chemical origin of nanoscale polar domains inPbZn1∕3Nb2∕3O3

2006

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“…The only limitation is the extent to which the MC energy can be made to realistically represent the real system energy. At one extreme, a very simplified model may be useful in demonstrating particular qualitative effects (Welberry, 2001) while, at the other, a quantitative and very detailed description of a disordered structure can be obtained .…”

Section: Interpretation and Analysismentioning

confidence: 99%

The interpretation and analysis of diffuse scattering using Monte Carlo simulation methods

Welberry

Goossens

2007

Acta Cryst Sect A

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Studies of diffuse scattering had a prominent place in the first issue of Acta Crystallographica 60 years ago at a time when conventional crystallography (determination of the average structure from Bragg peaks) was in its infancy. Since that time, conventional crystallography has developed enormously while diffuse-scattering analysis has seemingly lagged well behind. The paper highlights some of the extra difficulties involved in the measurement, interpretation and analysis of diffuse scattering and plots the progress that has been made. With the advent of the latest X-ray and neutron sources, area detectors and the ever-increasing power of computers, most disorder problems are now tractable. Two recent contrasting examples are described which highlight what can be achieved by current methods.

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“…These have included occupational disorder, [3] stacking faults, [4] atomic size-effect relaxation, [5] thermal disorder, [6,7] and strain. [8] The only limitation of the method is the degree to which the MC energy can be made to mimic the energy of the real system. At one extreme, a very simplified model may be useful in demonstrating particular qualitative effects, [9] while at the other, a quantitative and very detailed description of a disordered structure can be obtained.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo and Molecular Dynamics Simulation of Disorder in the Ag+ Fast Ion Conductors Pearceite and Polybasite

Welberry

Paściak

2010

Metall Mater Trans A

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The pearceite-polybasite group of minerals (i.e., pearceite, antimonpearceite, arsenpolybasite, and polybasite) of general stoichiometry [M 6 I T 2 III S 7 ][Ag 9 I Cu I S 4 ], with M = Ag + , Cu + and T = As 3+ , Sb 3+ , occur relatively commonly in nature. All have recently been shown to exhibit Ag + fast ion conduction at rather low temperatures (only slightly above or below room temperature [1] ). The average crystal structure determination of these materials shows the positions of the Ag + ions to be smeared out or delocalized within sheets in an ordered framework structure comprised of the other ions. At the same time, strong and highly structured diffuse scattering has been observed, which contains diffuse peaks that are incommensurate with the diffraction peaks of the framework structure. In order to try to understand the origins of the fast ion conduction properties of these materials, we have used computer simulation of a model system (Monte Carlo and molecular dynamics (MD)) to analyze this observed diffuse scattering.

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Diffuse X-ray scattering and strain effects in disordered crystals

Cited by 25 publications

References 16 publications

Chemical origin of nanoscale polar domains inPbZn1∕3Nb2∕3O3

Chemical origin of nanoscale polar domains inPbZn1∕3Nb2∕3O3

The interpretation and analysis of diffuse scattering using Monte Carlo simulation methods

Monte Carlo and Molecular Dynamics Simulation of Disorder in the Ag+ Fast Ion Conductors Pearceite and Polybasite

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