CHARACTERISTIC VOLUME EXPANSION OF POINT DEFECTS IN KBR

The change in volume of crystals of KBr, x irradiated at low temperature, has been measured using a capacitive dilatometer. Simultaneous measurement of volume expansion and optical density permitted a determination of the relaxations around individual defect pairs. By assuming that the F-center Frenkel pair relaxation volume was constant between 78 and 5 K, and by using previously measured values for the α-center and F-center relaxations, the relaxations around the interstitial defect could be evaluated. It was found that at 78 K the F-center associated interstitial had a relaxation (0.7±0.3)12a3. Over the temperature range 5-30 K, an apparent change in the relaxation due to the α-center Frenkel pair is observed. Optical bleaching of the F band between 5 and 20 K produced no change in the crystal volume. A possible reason for this is presented. © 1969 The American Physical Society.