Abstract
The effect of the ionic radius of trivalent impurities on the reorientation parameters of tetragonal charge-compensation centers in Ca is studied. As it has been found in an earlier paper that electrical dipole-dipole interaction between the centers significantly modifies the reorientation behavior of dipoles, we have included this perturbation in our analysis of the results of the ionic-thermocurrents experiments. From the results we conclude that in there is an appreciable tendency of the impurities to coagulate to clusters; in contrast to results given in the literature the characteristic relaxation time associated with the jumping dipoles does not depend on the size of the trivalent impurity. The activation energy however increases with increasing radius and the trend found for tetragonal centers in Ca is the same as for Sr observed by van Weperen and den Hartog. It is suggested that the variations are due to changes in the screening of the effective positive charge of the trivalent impurity.
- Received 31 October 1978
DOI:https://doi.org/10.1103/PhysRevB.19.4162
©1979 American Physical Society