The small signal ac response of the ionic conductivity growth process was described using the ionic admittivity defined as the (complex) ratio of the ac components of ionic current density and field since, unlike the ratio of current and voltage (admittance), this gives results independent of film thickness. Ideally constant ac and de components of field were approx imated by applying a ramp plus an ac voltage increasing with the average film thickness. Growth due to the ac ionic current produces an out of phase component of thickness giving a series capacitance effect. The measured current density includes the electric displacement current density. When corrected for these effects, plots of the real vs. the imaginary part of the ionic admittivity at a given de current density were well represented as arcs of circles with centers above the real axis. The ionic admittivity could thus be described using A + B/{1 + (j omega tau(m))(1-0)}, where 1/tau(m) is the angular frequency (omega) corresponding to the maximum imaginary part and pi(1 - theta) the central angle subtended by the arc. tau(m)(E, T) was not far from inversely proportional to the de ionic current density independent of temperature.