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On the Electrical and Magnetic Properties of Coloured and Uncoloured Calcium Fluoride Crystals
Author(s) -
Ratnam V. V.
Publication year - 1966
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19660160221
Subject(s) - diamagnetism , irradiation , paramagnetism , dielectric , crystal (programming language) , materials science , context (archaeology) , absorption band , conductivity , analytical chemistry (journal) , electrical resistivity and conductivity , chemistry , condensed matter physics , optics , magnetic field , optoelectronics , organic chemistry , physics , quantum mechanics , nuclear physics , computer science , biology , programming language , paleontology , electrical engineering , engineering
The electrical and magnetic properties of uncoloured calcium fluoride crystals and of specimens of these crystals coloured by X‐rays and electrolysis, are reported. The dc conductivity and dielectric loss measurements of uncoloured and X‐ray coloured CaF 2 crystals show that in a freshly prepared crystal 1. the number of free negative ion vacancies is very small and 2. the anti‐Frenkel defects which are initially present are in the associated form. These points explain why, for irradiation at room temperature, the α‐band (the F‐band of this system) is not observed in optical absorption. The nature of the traps is also discussed in the context of the observed changes in the dc conductivity accompanying the thermal bleaching of the colour centres in an X‐irradiated crystal. The temperature variation of the magnetic susceptibility indicates that X‐irradiation produces both paramagnetic and diamagnetic colour centres. From the results of measurements on electrolytically coloured crystals, the oscillator strength of the F‐band is estimated as about 10 −2 ; this also explains why the formation of the α‐band is not detected for room temperature X‐irradiation.