摘要:

Two ongoing experiments dealing with ionic surface charge effects in AgCl and AgBr are described. The first consists of a mapping of the depth profile of the electrostatic potential in macroscopic single crystals, using as a probe the distribution of trace levels of radioactive, divalent54Mn. The crystals are sectioned chemically after aging, with a depth resolution of 10 Å, using the radiotracer36C1 as a depth gauge. The resulting potential profiles agree with theoretical expectation. The effects of temperature, dopants, and surface orientation are now being investigated. The second experiment is a study of the effects of adsorbents (such as photographic dyes) and surface treatments (e.g., transient exposure to water or methanol) on the sub-surface space charge, as manifested through changes in the longitudinal conductance of evaporated thin films (about 4000 Å) of AgBr. Rather large effects have been observed, sometimes corresponding to a change in the space charge contribution to the conductance of about a factor of ten, thus reflecting the change in the distribution of charged jogs at the surface.

ISSN:0033-7579    

DOI:10.1080/00337578308224677

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The energies which control the diffusion of univalent impurities in AgCI and AgBr have been determined using atomistic simulation methods. These are: the Frenkel defect formation energy, the activation energy for the jump of the impurity ion, and the association energy of the impurity ion with a nearest-neighbour vacancy. Their variation with temperature has been evaluated in the quasi-harmonic approximation. These energies have been used to calculate the diffusion coefficients of Na+ and Cs+ in AgCI and of Na+ and Rb+ in AgBr and the results are compared with experimental data. The effects on the diffusion rate of Na+ in AgCI of changes in the concentrations of both sodium and a divalent impurity (cadmium) have also been determined.

ISSN:0033-7579    

DOI:10.1080/00337578308224678

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The results of the recent experiments on the diffusion of K+and Rb+in both AgCl and AgBr are discussed. The diffusion Arrhenius plots for K+show an anomaly at high temperatures which quantitatively replicates that displayed by the ionic conductivity presumably originating from the nonlinear temperature dependence of the free energy of Frenkel defect formation. However, this “inherent curvature” is not observed in case of the diffusion of Rb+in both the halides, as it is indeed true for most other diffusions of cations. These results are then compared with the published results of the diffusion study of other impurity cations. It appears that additional temperature dependence of the free energy of migration and association need to be considered to have a unified explanation for the variety of diffusion results.

ISSN:0033-7579    

DOI:10.1080/00337578308224679

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Measurements of self diffusion coefficients of42K,85Rb and125I and measurements of ionic conductivity were carried out on single crystals of the (Rb2K1-Z)I solid solutions (z varying from 0 to 1). The self-diffusion coefficient measurements (T=875 K) indicate that two types of cation have the same mobility and that this mobility is about twice that of the anion. All these mobilities are higher for the solid solutions than for the pure components, KI and RbI. The ionic conductivity was analysed using the Schottky defect model. Interactions between defects were taken into account in this analysis. Thus, enthalpies and entropies of formation and migration of vacancies were determined. Examining the variations of these parameters as functions of composition z at a given temperature shows that the density of vacant sites is significantly higher in the case of solid solutions than in the case of pure components (for example, this density is about twice as large for (Rbo.sK0.5)I as for KI or RbI).

ISSN:0033-7579    

DOI:10.1080/00337578308224680

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Li+ions in MgF2take on different forms in different temperature ranges At low temperatures, they are primarily present as Li-Li dumbbell pairs replacing a single Mg2+ion This defect manifests itself by a characteristic internal friction peak At intermediate temperatures (300-600°) the pairs begin to dissociate and the ionic conductivity parallel to thec-axis is determined by interstitial Li+(Lni) which moves rapidly in open channels of the rutile structure At high temperatures (∼900°) diffusion experiments show that cation vacancies (VC) accompany the Li, and therefore, that the conversion reaction LiS↪Lii+Vcgoes almost to completion (Here Lismeans substitutional Li+.) It is shown that the enthalpy of this reaction is <0.88 eV.

ISSN:0033-7579    

DOI:10.1080/00337578308224681

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The small-signal a.c. response of cells with LaF3or a solid solution La1-xBaxFa-x(0≤x≤0.104) and ionically blocking electrodes has been measured in the frequency range 10-2to 105Hz, and for temperatures from 293 to 1300 K. At low and moderate temperatures the a.c. bulk response can be modeled with a Debye circuit. We have studied localized motions in LaF3and the solid solutions using thermal depolarization techniques (T.S.D.C.) in the region 4 to 300 K. The T.S.D.C.-spectra reveal at least two dipolar relaxations, three other relaxations, and a peak due to relaxation of macroscopic space-charge.

ISSN:0033-7579    

DOI:10.1080/00337578308224682

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The aim of the present study is to establish correlations between the electrical and structural properties in Rb1-XBiXF1+2Xand RbBi3F10. Nuclear magnetic resonance and neutron diffraction have proved to be helpful techniques. They have allowed us to obtain consistent results which account for the evolution of ionic conductivity properties with amount of substitution.

ISSN:0033-7579    

DOI:10.1080/00337578308224683

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

We present results of single crystal neutron diffraction studies of lanthanum and erbium doped CaF2. Difference Fourier maps reveal well-resolved interstitial structures. The results demonstrate trends in cluster structure with both dopant radius and with temperature and are in line with the predictions of computer simulation studies.

ISSN:0033-7579    

DOI:10.1080/00337578308224684

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

High resolution triple-axis neutron spectroscopy has been used to make a detailed investigation of the incoherent scattering from mobile anions in the fast-ion phase of strontium chloride. The quasielastic energy broadening has been measured as a function of the scattering vector at temperatures of 1001, 1053 and 1087 K. The data have been analysed in terms of the jump diffusion model of Chudley and Elliott, and the encounter model of Wolf. A vacancy diffusion mechanism is found to predominate in the fast-ion phase, with anion hops mainly to nearest neighbour and next-nearest neighbour regular anion sites.

ISSN:0033-7579    

DOI:10.1080/00337578308224685

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Neutron and X-ray diffraction studies reveal that fcc LJ2SO4, bcc LiNaSO4, and bcc LiAgSO4 are characterized by a strong rotational disorder of the sulphate ions which strongly enhances the mobility of the cations. Single crystal neutron scattering studies have been performed on fee Li2SO4 and the quasielastic scattering supports the previous conclusions, and more detailed information should be obtainable by this technique. The elastic constants of fee Li2SO4 have been determined by Brillouin scattering. The information obtained so far by Raman scattering concerning the motion of lithium ions in fcc Li2SO4 supports earlier conclusions from conductivity measurements.

ISSN:0033-7579    

DOI:10.1080/00337578308224686

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor