1/f Conductance Fluctuations in Aqueous Ionic Solution

Abstract

Conductance fluctuations were observed in CuSO₄ aqueous ionic solutions over ion concentrations from 5×10⁻⁴ to 10⁻² mol/l. It is found that the spectral density is approximately 1⁄f for ion drift velocities smaller than a critical value which is of order of 10⁻³ m/s; above this value it approaches a Lorentzian form. The α-value of the 1⁄f fluctuation is approximately proportional to the ion concentration when it is larger than 10⁻³ mol/l; below this critical value the α-value seems to take a constant value 2.5×10⁻². The existence of the critical ion concentration suggests that, if the 1⁄f conductance fluctuations are caused by mobility fluctuations, the 1⁄f conductance fluctuation has a coherence length, which is estimated to be 10 nm.