Structural changes in silver bromide at the melting point

Nield, V. M.; Keen, David A.; Hayes, W.; McGreevy, R.L.

doi:10.1088/0953-8984/4/32/005

Cited by 66 publications

(65 citation statements)

References 15 publications

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“…In [12] we suggested that the effect should be explained in terms of the frequent hopping of silver ions from their regular octahedral lattices sites into tetrahedral inter stitial sites and back again, i.e., by the frequent cre ation and recombination of Frenkel pairs. This inter pretation would be in agreement with structural data showing significant silver-ion probability density be tween lattice sites and interstitial sites [15][16][17].Our present measurements include angular fre quencies that are of the order of, and even larger than, the inverse time constant of the Debye-type process. In fact, the numerical value of this time constant has been unknown up to now.…”

supporting

confidence: 91%

Creation and Recombination of Frenkel Defects in AgBr

Funke

Lauxtermann

Wilmer

et al. 1995

Zeitschrift Für Naturforschung A

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Dedicated to Professor Ewald Wicke on the occasion of his 80th birthdayComplete ionic conductivity spectra as well as quasielastic and inelastic neutron scattering spectra have been taken of solid silver bromide at various temperatures. High-amplitude vibrational move ments, essentially of the silver ions, contribute to both kinds of spectra. In particular, a conductivity maximum, located at about 500 GHz, reflects oscillations of individual silver ions along <111 > directions. -The microwave and millimetre-wave conductivities are dominated by a thermally ac tivated Debye-type relaxation process. The effect is consistently explained by the frequent hopping of silver ions from regular octahedral lattice sites into tetrahedral interstitial sites and back again, i.e., by the frequent creation and recombination of Frenkel pairs. -The effect is also responsible for the existence of thermally activated quasielastic components in the neutron scattering spectra. The width of the coherent quasielastic scattering shows that the forward-backward hopping of a silver ion is accompanied by fast correlated movements of ions in its immediate neighbourhood.C r e a tio n a n d R e c o m b in a tio n o f F r e n k e l D e fe c ts in A g B r I. IntroductionSilver bromide, AgBr, is one of the most thoroughly studied solid electrolytes, see for instance [1]. It is a fast ionic conductor at temperatures well below its melting point, with a conductivity of 0.1 f t-1 cm-1 at about 625 K [2-4], The cation mobility in AgBr is caused by the thermally activated formation of Frenkel defects in the rocksalt structure, the Frenkel-pair formation enthalpy being about 1.15 eV [5,6]. On the basis of temperature dependent conductivity and tracer diffu sion data as well as model calculations, various migra tion enthalpies have been derived, the lowest applying to the collinear interstitialcy mechanism [7, 8], In 1961 Everett et al. [9] published microwave con ductivity data of AgBr, taken at 23 GHz. The conduc tivity was found to be significantly larger at 23 GHz than at 1 kHz [2][3][4], and the effect was attributed to a Debye-Falkenhagen type of relaxation [10,11] of the mobile silver ions. In an effort to substantiate the findings of Everett et al. we have performed conduc tivity measurements in a broad frequency range. While our earlier data were restricted to frequencies below 60 GHz [12], we now present complete conduc tivity spectra which also comprise the millimetre-wave and far-infrared frequency regimes, up to 10 THz. Our data corroborate the existence of a pronounced con ductivity dispersion at microwave frequencies. HowReprint requests to Prof. Dr. K. Funke. ever, as already stated in [12], they clearly do not bear the distinguishing marks of a Debye-Falkenhagentype jump relaxation process; these would include a power law frequency dependence of the conductivity with an exponent of less than one, see, e.g., [13,14], Instead, the observed frequency-dependent conduc tivity seems to follow a power law with an exponent of two, which is ty...

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supporting

confidence: 91%

Creation and Recombination of Frenkel Defects in AgBr

Funke

Lauxtermann

Wilmer

et al. 1995

Zeitschrift Für Naturforschung A

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“…This could be attributed to the difference detected in the position of the minimum for the pair potential. It is also stressed here that the present result of the inter-atomic distance for the nearest neighbor Ag±Br pair agrees well with the values determined by neutron diffraction [12,13].…”

Section: Molten Agbrsupporting

confidence: 90%

Effective pair potentials of Molten AgBr, CuBr, CuI and RbBr estimated from the experimental partial structure factors

Mitev

Saito

Waseda

2002

Science and Technology of Advanced Materials

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The effective pair potentials of molten AgBr, CuBr, CuI and RbBr have been obtained from measured structural information by solving the modi®ed hypernetted-chain (MHNC) equation coupled with a predictor±corrector method, recently proposed for a binary system. The usefulness of the pair potentials obtained in this work was suggested by reproducing the particular pre-peak in the partial structure factor of Cu±Cu pair in molten CuBr and CuI, because such pre-peak could not be given while using the model potentials previously proposed for these two molten salts. Some characteristic features in these four molten salts were also detected in the bridge function, which was introduced to the MHNC equation as a many-body interaction contribution. q

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“…15.48 As for AgCl and AgBr, the ionic conductivity is due to the cationic Frenkel defects, and it is suggested that a possible diffuse transition to a superionic state is frustrated by the disordering of the anionic sublattice due to Schottky defects which leads to melting. 49,50 This behavior may be because the size difference between cations and anions in CuCl is less pronounced than in AgI and CuI, and also because the chloride polarizability s lower than the iodide one. To answer this question would be necessary to carry out MD simulations of CuCl before melting using non-cubic boundary conditions, which are not available in our own programs, as it is the case in many standard MD simulation software.…”

Section: Discussionmentioning

confidence: 99%

The structure of molten CuCl: Reverse Monte Carlo modeling with high-energy X-ray diffraction data and molecular dynamics of a polarizable ion model

Alcaraz

Trullàs

Tahara

et al. 2016

The Journal of Chemical Physics

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The results of the structural properties of molten copper chloride are reported from high-energy Xray diffraction measurements, reverse Monte Carlo modeling method and molecular dynamics simulations using a polarizable ion model. The simulated X-ray structure factor reproduces all trends observed experimentally, in particular the shoulder at around 1 Å -1 related to intermediate range ordering, as well as the partial copper-copper correlations from the reverse Monte Carlo modeling, which cannot be reproduced by using a simple rigid ion model. It is shown that the shoulder comes from intermediate range copper-copper correlations caused by the polarized chlorides.2

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Structural changes in silver bromide at the melting point

Cited by 66 publications

References 15 publications

Creation and Recombination of Frenkel Defects in AgBr

Creation and Recombination of Frenkel Defects in AgBr

Effective pair potentials of Molten AgBr, CuBr, CuI and RbBr estimated from the experimental partial structure factors

The structure of molten CuCl: Reverse Monte Carlo modeling with high-energy X-ray diffraction data and molecular dynamics of a polarizable ion model

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