POLARIZATION CAPACITANCE AND DISTORTION IN KBr AT LOW FREQUENCIES

Abstract

A bridge to measure high impedances in the frequency range 0.01 to 100 Hz is described. The conductance and capacitance of calcium doped KBr single crystals were measured between 50 and 330 °C. The polarization capacitance was not inversely proportional to the square of the thickness, a condition expected from the linearized theory. Severe harmonic distortion was observed at low frequencies, and was attributed to the onset of space-charge control following completion of a vacancy monolayer at the surface, forming a blocking boundary. At the higher frequencies this monolayer is not completed, the crystal boundaries are not blocking, and distortion is not observed. An expression is derived for the limiting frequency at which distortion sets in, and is shown to be in good agreement with experiment.