Dielectric loss and electrical-conductivity studies on copper-doped NH4Cl crystals

Abstract

A study of copper impurity centres in NH₄Cl by dielectric loss and electrical-conductivity measurements is reported in this paper. A theory is given for the dielectric loss due to the reorientations of impurity-vacancy dipoles in a CsCl-type lattice by means of jumps of constituent point defects. Expressions are worked out for tan δ associated with various complexes with substitutional and interstitial divalent impurities by considering the atomic kinetics of reorientations. NH₄Cl: Cu crystals grown from ammoniacal and acidic solutions give one set of loss peaks each and crystals grown from neutral solutions give two sets of loss peaks. These peaks are attributed to two types of interstitial copper centres.

In crystals grown from neutral solutions suppression of the electrical conductivity with respect to pure crystals is observed. The results are interpreted in terms of anion vacancy motion in the intrinsic region and cation vacancy motion in the extrinsic region and a minimum limit of 2.06 eV is suggested for the Schottky defect-formation energy.