Abstract
AbstractAlthough aggregation of impurity centres in doped alkali halides upon X‐irradiation is proposed earlier, direct evidence of such centres having dipole moment is reported here for the first time by the method of ionic thermocurrents (ITC). The norma Idipolar relaxation band in KCl: Pb is located around 224 K, while sometimes a small band at about 160 K is found in the ITC spectrum of heavily doped systems. Exposure to X‐rays increases this band around 160 K at the cost of the 224 K dipolar band. Optical absorption in the A‐band of KCl:Pb, along with ITC measurements indicates that higher aggregates of I–V dipoles are easily formed in heavily doped systems. Formation and growth of the 160 K ITC band upon X‐ray irradiation are explained from the fact that the effect of X‐irradiation is to increase the rate of aggregation of I–V dipoles, through temporary electron trapping by lead ions.
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