Diffusion coefficients of two mobile ions are computed from the conductivity variation with time of three In-rich chalcopyrite single crystals of the AB(n-3)In(n+1)VI(2n) system (AB = Cu and Ag and VI = Se or Te). The coefficients have similar values in the three compounds, higher than in chalcopyrite compounds (ABInSe(2)) due to a higher number of (2V(Cu) + In-Cu) defect pairs in the lattice. In each compound, the potential across the sample or the current intensity, V-m and I, can increase or decrease within time due to a change in the interface potential by the ion arrival, where the decrease could be explained by a charge decrease. Mobile ions arrive while others, with higher charge, should leave related to the formation or disappearance of (2V(Cu) + In-Cu) defect pairs. Compositional measurements confirm the motion of Cu ions and In antisites, In-Cu, in the Cu sublattice. Therefore, these compounds are mixed ionic and electronic conductors, MIECs, with two mobile ions, where the electronic and ionic conductions are non-blocked and blocked in the metal/semiconductor interface respectively. An equivalent electrical circuit is proposed, extensible at MIECs with j mobile ions, where the interface potential is similar to the potential drop in the charge or discharge in the capacitor. The analysis of the total flux of ions due to diffusion, j(diff), and to the action of electrical field, j(drift), permits compute the number of ions, their diffusion coefficients and the change of the potential drop within time in the interface in compounds with several mobile ions. This electrical model is checked using the experimental data in the three single crystals in a computer program. To know different mobile ions in In-rich chalcopyrites and their diffusion coefficients will permit to understand and have mechanisms of control in solar cell fabrication based in chalcopyrite thin films. (C) 2012 Elsevier B.V. All rights reserved.