Critical Temperatures in the Photorefractive Polymer Composite Behavior

Two critical temperatures, T1 and T2, which limit the range of the photorefractive (PR) response of polymer composites, have been determined from temperature dependence studies of the ac conductivity. T1 represents the calorimetric glass transition temperature and sets the level under which chromophore orientation is drastically reduced. T2 sets the level above which conduction mechanisms become dominated by temperature. In this study, we stress the importance of the T2 parameter, generally ignored in literature, and the advantages of using dielectric spectroscopy to obtain both critical temperatures from a single experiment. In addition, impurity diffusion processes, which play an important role in PR property optimization, have been identified from the frequency dependence of the ac conductivity.