Point Defect Parameters for Calcium Fluoride From Ionic Conductivity Measurements at Low Temperatures

Jacobs, P. W. M.; Ong, S.H.

doi:10.1051/jphyscol:1976777

Cited by 20 publications

(8 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ure indicated that his analysis of the conductivity data could lead to substantial errors in the values for the interstitial mobility, since a correction had to be made for conduction of fluoride interstitials along grain boundaries. A detailed study and analysis of the conductivity of CaF 2 appeared more recently, and revealed numerical values for defect parameters that are consistent with the data reported by Bollmann and co-workers [23].…”

Section: Cafsupporting

confidence: 72%

Retarded ionic motion in flourites

Schoonman

1980

Solid State Ionics

View full text Add to dashboard Cite

Metal halides with the fluorite structure attain conductivity values typical of ionic melts far below their melting points, and also go through a second-order transition. Conductivity data for the fluorites are reviewed, and it is shown that the anion vacancies have a large and unique mobility value at the transition temperatures T c. At T c only small concentrations of defects are present, which strongly contradicts the concept of anion-sublattice melting. The conductivity mechanism above T c is discussed in relation with the enhanced ionic motion model developed for concentrated anion-excess solid solutions based upon fluorites. As a consequence of unusually large defect mobilities at T c it is noted that retard ionic motion occurs above T c.

show abstract

Section: Cafsupporting

confidence: 72%

Retarded ionic motion in flourites

Schoonman

1980

Solid State Ionics

View full text Add to dashboard Cite

show abstract

“…It is to be emphasized that the activation energy, 0.502 el7, is similar t o that for "free"-vacancy migration in calcium fluoride, which has been found to lie in the range 0.35 to 0.55 eV [2].…”

Section: It Was Found That For Each Temperature the Most Probable Relmentioning

confidence: 97%

Activation Volume for Vacancy Motion in Calcium Fluoride

Fontanella

Wintersgill

Andeen

1980

Physica Status Solidi (b)

View full text Add to dashboard Cite

The audio frequency complex dielectric constant for sodium doped calcium fluoride is measured a t pressures up t o 0.4 GPa over the temperature range 240 to 270 K and a t zero pressure over the temperature range 5.5 to 400 K. Consequently, t,he reorientat,ion of a nearest-neighbor vacancy around a substitutional sodium ion is studied. The activation volume for the motion is found t o be (1.73 f 0.1) cm3/mol. It is argued that this value should be similar to the migration volume for "free" vacancies. The compressibility of the activation volunw is found t o be forty times the cornpreesibility of the host lattice. Finally, a large negative thermal expansion coefficient is found for the activation volume for vacancy motion.

show abstract

“…cm -2 ) t/(eV) E F (eV) AE" (eV) AE,-(eV) Table 3. Perfect-crystal and anion-defect quantities (e 0 , e x static and high-frequency dielectric constants, c, y elastic constants, U cohesive energy per unit cell, relative to free ions, E F Frenkel formation energy, A£ v , AE, vacancy and interstitial migration energies, calculated from the potential model and and compared with the experimental results listed by Catlow and Norgett (1973) and by Jacobs and Ong (1976). …”

Section: Interaction Modelsmentioning

confidence: 99%

Dynamical Simulations of Superionic Conductors

Gillan

1989

Series on Directions in Condensed Matter Physics

View full text Add to dashboard Cite

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.

show abstract

Point Defect Parameters for Calcium Fluoride From Ionic Conductivity Measurements at Low Temperatures

Cited by 20 publications

References 12 publications

Retarded ionic motion in flourites

Retarded ionic motion in flourites

Activation Volume for Vacancy Motion in Calcium Fluoride

Dynamical Simulations of Superionic Conductors

Contact Info

Product

Resources

About