Non-linearity in NaCl single-crystal films

Abstract

Epitaxial Ag/NaCl/Ag capacitors have been fabricated on hot NaCl substrates and their dielectric properties have been measured. Only one loss peak in the relaxation spectrum of the epitaxial films has been observed, which has been attributed to the blocking of cation vacancies at the electrode-dielectric interfaces. The activation energy associated with the loss peak has been calculated, and is of the order of 0.83 ± 0.1 eV. The charge carrier concentration has been estimated to be about 10 24 m −3. The increase in capacitance observed at low frequencies suggests that the formation of space charge is responsible for the polarization in alkali halides. A strong non-linearity is associated with the polarization and has been observed in the form of variations of dielectric loss and capacitance in alkali halide films. Harmonic generation and cut-off in the current through the alkali halide epitaxial capacitors have been observed. All these observations imply that the space charge polarization mechanism is predominant in alkali halide films. A built-in potential of several hundred millivolts across the freshly prepared epitaxial capacitor has been observed, and this causes an asymmetry in the electrical behaviour. No evidence of vacancy pair orientation has been found and the results have been attributed to the migration of cation vacancies through the whole thickness of the epitaxial film with subsequent blocking at the electrodes to form a space charge.