Conductivity dispersion in supercooled calcium potassium nitrate: caged ionic motion viewed as part of standard behaviour.
Conductivity spectra of ionic materials with disordered structures are usually thought to consist of several parts, i.e., the DC conductivity, a power-law component, a nearly-constant-loss feature (if identified) and the (far-)infrared conductivity caused by vibrational motion. Such a decomposition may, however, easily lead to a misinterpretation of the underlying dynamics. Here, we discuss broad-band conductivity data of the supercooled glass-forming melt calcium potassium nitrate, of composition 0.4 Ca(NO(3))(2).0.6 KNO(3), often abbreviated as CKN. Data have been taken at frequencies up to the far infrared. We show that the frequency-dependent conductivity is very well reproduced by a superposition of only two components. One of them is due to vibrations, the other is caused by displacements of the mobile ions. The latter component, which does not follow a power law, is described in terms of a physical model called the MIGRATION concept. This model treatment has been found to apply in many solid electrolytes as well and is, therefore, considered to provide a "standard" formulation of the ion dynamics. The gradual transition from a correlated forward-backward ("caged") ionic motion to a stepwise translational motion may be regarded as the main feature of the MIGRATION concept.
Funke
Klaus
K
Institute of Physical Chemistry and Sonderforschungsbereich 458, University of Münster, Corrensstrasse 30, D - 48149, Münster, Germany. k.funke@uni-muenster.de
Singh
Prabhakar
P
Banhatti
Radha Dilip
RD
D000465:Algorithms; D017610:Calcium Compounds / Q000737:chemistry*; D003080:Cold Temperature; D004058:Diffusion; D004553:Electric Conductivity; D004735:Energy Transfer; D005898:Glass / Q000737:chemistry*; D007259:Infrared Rays; D008564:Membrane Potentials; D008956:Models, Chemical; D009038:Motion; D009566:Nitrates / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000032:analysis / Q000737:chemistry
D017610:Calcium Compounds; D009566:Nitrates; D017680:Potassium Compounds; D014867:Water; C059948:calcium nitrate; C023844:potassium nitrate