An electronic system based on quadrature oscillator, current-to-voltage converter and phase sensitive detector (PSD) has been designed and constructed for measurement of AC electrical conductivity and complex impedance/admittance on ionic and superionic conductors at several frequencies upto 60 kHz. The design incorporates a CMOS FET switch controlled by two anti-square reference signals for rectification and a differential amplifier for summation and impedance matching. The performance of the system has been demonstrated and the measurement possibilities discussed.

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.