Unification of bulk and interface electroresistive switching in oxide   systems
  We demonstrate that the physical mechanism behind electroresistive switching in oxide Schottky systems is electroformation, as in insulating oxides. Negative resistance shown by the hysteretic current-voltage curves proves that impact ionization is at the origin of the switching. Analyses of the capacitance-voltage and conductance-voltage curves through a simple model show that an atomic rearrangement is involved in the process. Switching in these systems is a bulk effect, not strictly confined at the interface but at the charge space region. 
A. Ruotolo, C. W. Leung, C. Y. Lam, W. F. Cheng, K. H. Wong and G. P.   Pepe