MICROWAVE-ABSORPTION IN INSULATING DIELECTRIC IONIC-CRYSTALS INCLUDING THE ROLE OF POINT-DEFECTS

A theoretical model of microwave absorption in linear dielectric (nonf erroelectric) ionic crystals that takes into account the presence of p oint defects has been synthesized and specifically applied to NaCl sin gle crystals by considering all relevant interaction mechanisms betwee n a harmonic electric field and single-crystal ionic crystalline solid s, including ionic conduction, dielectric relaxation, and multiphonon processes. The loss factor epsilon '' f has been measured by a cavity resonator insertion technique for nearly pure and Ca2+ doped NaCl sing le crystals at frequencies from 2 to 16 GHz and at the temperatures fr om 300 to 700 K. The experimental results are in good agreement with t he theoretical model. The theoretical model predicts a transition betw een low- and high-temperature absorption processes that may partly acc ount for the phenomenon of thermal runaway observed during microwave p rocessing of ceramics.