DIELECTRIC RELAXATIONS IN ADDITIVELY COLORED KCL AND KCL:SRCL2 CRYSTALS.
Abstract
The dielectric relaxations of additively colored alkali halides have been investigated by means of ionic thermocurrent (I. T. C.) and optical absorption measurements. In addition to the ITC bands present in non-colored KCl crystals, several new bands were found when F centers were partially vonverted to other centers such as F', M, N, R, Z, Z1, Z2, and Z3, by F-light irradiation at various temperatures. These additional ITC bands were found to be due to the migration of electrons rather than to the orientation of ionic dipoles. In the particular case of the Z2 centers, which can be obtained only in crystals containing metallic divalent impurities, ITC and field-induced dicroism measurements did not provide any evidence for the existence of an electric dipole moment of the Z2 center itself.Quantitative measurements of the impurity-vacancy dipole (I. V.) concentrations in KCl:SrCl2 crystals indicate, in addition, that the growth of the Z2 centers is accompanied by a decrease of the I. B. band. The proportionality constant between the number of Z2 centers created and the number of I. V. dipoles destroyed during the F to Z2 conversion was slightly more than three. These results support a model for the Z2 center having spherical symmetry and suggest that the process of formation of the Z2 centers is closely related to the association of I. V. dipoles into trimers. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1966
- Accession Number
- AD0635005
Entities
People
- Cesare Bucci
Organizations
- University of Pennsylvania