Investigation of anion disorder in PbF<sub>2</sub>at high temperatures by neutron diffraction

Dickens, Michael; Hayes, W.; Hutchings, M. T.; Smith, Chris

doi:10.1088/0022-3719/15/19/006

Cited by 63 publications

(47 citation statements)

References 22 publications

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“…Some of the problems are discussed by Hayes and Hutchings. In spite of this, a detailed and painstaking analysis of diffraction data for superionic PbF 2 has been presented by Dickens et al (1982), which appears to give enough information to yield the p a (r) themselves. The procedure is to set up a parameterized model for the p a (r) and perform a least-squares fit to the measured /(G).…”

Section: Fag) = N'i (E Txpiig-rj) mentioning

confidence: 99%

Dynamical Simulations of Superionic Conductors

Gillan

1989

Series on Directions in Condensed Matter Physics

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Superionic conductors are ionic solids in which one ion species is disordered andhighly mobile. Molecular dynamics (MD) simulation gives a powerful way of studying models of superionic conductors. We explain the MD technique and describe how it is applied to ionic systems. We than show how simulation of fluorite superionic conductors has successfully reproduced a range of experimental measurements on quantities including the diffusion coefficient, the spatial distribution of disordered ions, the van Hove self-function and the dynamical structure factors. The simulations have been used to provide a unified interpretation of the observations. This shows that superionic conduction in fluorites occurs by the motion of vacancy and interstitial defects, both of which jump between regular lattice sites, the coherent quasielastic peak recently observed by neutron scattering is shown to arise from the motion of these defects. Ionic Solids at High Temperatures Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 09/30/15. For personal use only. 170 IntroductionAll crystalline materials show some degree of disorder at high temperatures. This disorder is of two kinds: firstly, there are vibrational displacements of the ions from their regular sites, and secondly, there are point defects. The presence of point defects -vacancies and interstitials -is responsible for the diffusion of ions that is observed in all ionic crystals. Vibrational motions are usually treated in the harmonic approximation, which assumes that the displacements are small. As one goes to higher temperatures, this approximation becomes less and less valid and anharmonic effects become important: the lattice parameter depends on temperature, the constant-pressure and constant-volume specific heats differ, and the vibrational modes become damped. A more sophisticated theoretical description is then called for -an example is the self-consistent phonon approximation described by Ball elsewhere in this book. The point-defect disorder is also easiest to discuss when the temperature is not too high. One can then use energy-minimization techniques to determine the energies of formation and migration of the defects, and harmonic theory to calculate the associated entropies. These highly successful methods are discussed in the article by Harding. Again, at very high temperatures one encounters difficulties, especially if the defect concentration becomes high and the defects begin to interact with each other.

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Section: Fag) = N'i (E Txpiig-rj) mentioning

confidence: 99%

Dynamical Simulations of Superionic Conductors

Gillan

1989

Series on Directions in Condensed Matter Physics

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“…However, neutron diffraction studies have shown that the empty cube center sites are not significantly occupied at temperatures in excess of T c and, instead, the anion interstitials within the Frenkel pairs favor sites between the midpoint of the two nearest-neighbor anion sites and the center of an anion cube in a h1 1 0i direction [72]. This defect model was supported by analysis of the coherent diffuse neutron scattering, which also showed that the Frenkel defects are accompanied by relaxations of nearest-neighbor lattice anions in h1 1 1i directions towards the centers of the adjacent empty anion cubes [73].…”

Section: Halide Fluoritesmentioning

confidence: 99%

Superionic Materials: Structural Aspects

Hull

2009

Solid State Electrochemistry I

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Superionic conductors are solids which show high levels of ionic conductivity, which often approach values more typical of ionic liquids. This behavior is associated with the presence of extensive dynamic disorder within the crystalline lattice, and the nature of the defects has long proved a challenge to both experimental and computational approaches. This chapter provides a short introduction to the major techniques used to probe the structure-property relationships within superionic conductors, highlighting the roles of X-ray diffraction, neutron diffraction, EXAFS, NMR, and molecular dynamics methods. The relative advantages and limitations of each method are briefly described, followed by a discussion of the major families of highly conducting compounds and an assessment of the current state of knowledge concerning their structural properties. OverviewThe high levels of ionic conductivity associated with superionic conductors, which often approach values more typical of ionic liquids, are associated with the presence of extensive dynamic disorder within the crystalline lattice. As a consequence, a full understanding of the interplay between the structural and conducting properties of these important materials requires a detailed characterization of both the long-range arrangement of the ions within the crystal lattice and the short-range ion-ion correlations within the defects. The presence of significant levels of disorder, which can be both intrinsic (thermally induced) and extrinsic (due to chemical doping) in origin, presents a challenge to the conventional experimental methods used to provide structural information. In the case of superionic conductors, no one technique can provide a complete picture, and it is often necessary to employ several complementary approaches, of which X-ray diffraction (XRD), neutron diffraction, Solid State Electrochemistry I: Fundamentals, Materials and their Applications. Edited by Vladislav V. Kharton

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“…It is the anharmonic thermal vibration model and confirmed using X-rays [2] and neutrons [3,4] diffraction methods.…”

Section: Introductionmentioning

confidence: 99%

The Structure and Ionic Conduction in Fluorite-Type Solid Solutions

Ito

1992

MRS Proc.

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The crystal structure of P-Pb 0 . 9 Bi 0 . 1 F 2 . 1 has been investigated in the temperature range 294 to 710K by single crystal X-ray diffraction method. Phase transition is observed at about 700K and the mean square displacements (MSD) of metal and fluorine ions show a rapid increase near the transition temperature. The fluorine ions do not show anharmonic thermal vibrations in the regular site in the temperature range.

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Investigation of anion disorder in PbF₂at high temperatures by neutron diffraction

Cited by 63 publications

References 22 publications

Dynamical Simulations of Superionic Conductors

Dynamical Simulations of Superionic Conductors

Superionic Materials: Structural Aspects

The Structure and Ionic Conduction in Fluorite-Type Solid Solutions

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Investigation of anion disorder in PbF2at high temperatures by neutron diffraction

Cited by 63 publications

References 22 publications

Dynamical Simulations of Superionic Conductors

Dynamical Simulations of Superionic Conductors

Superionic Materials: Structural Aspects

The Structure and Ionic Conduction in Fluorite-Type Solid Solutions

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Investigation of anion disorder in PbF₂at high temperatures by neutron diffraction