Premelting lattice disorder in AgBr and PbF2
1983; Elsevier BV; Volume: 11; Issue: 1 Linguagem: Inglês
10.1016/0167-2738(83)90062-0
ISSN1872-7689
Autores Tópico(s)Thermodynamic and Structural Properties of Metals and Alloys
ResumoThe behaviour of AgCl and AgBr is contrasted with that of fluorite-type crystals such as PbF2, which are also Frenkel conductors at low temperatures but undergo a diffuse transition to a superionic state before melting. Concentrating on AgBr for which some experimental information on all relevant defect parameters is available, a Debye-Hückel model for the interactions between defects, modified for saturation of screening at high defect concentrations, is used to show that the dominant cationic Frenkel disorder in the very hot solid can stimulate disorder in the bromine sublattice. It is suggested that this defect behaviour frustrates a superionic transition in AgBr and leads to melting accompanied by anomalously strong premelting phenomena. A comparative discussion is given for superionic PbF2, making contact with the estimates of defect concentrations which are available from neutron diffraction experiments.
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