Dielectric loss measurements on OH− dipoles in KBr with caloric techniques

The dielectric loss due to the reorientation of tunneling paraelectric defects in alkalihalides can be determined at low temperatures in a simple and sensitive way by measurement of the dissipated heat. The method was tested for OH− dipoles in KBr by measuring the heating rate as a function of the applied ac frequency and amplitude, variable dc bias, temperature and dipole concentration. The normalized heating versus frequency curves for small dipole concentrations follow closely a Debye peak, with relaxation time values in good agreement with earlier results. Asymmetric broadening of the heating curves, observed for high dipole concentrations, can be explained by the presence of interaction effects within local clusters of parallel ordered dipoles. Using this sensitive heating technique and crystals with low dipole concentration, a search was conducted for the decrease in dielectric loss, predicted by the tunneling model for fields comparable to the tunneling splitting E < 2 Δ/p.