Evidence for Increased Polaron Conduction Near the Cathodic Interface in the Final Stages of Electrical Degradation in SrTiO3 Crystals

The nature of charge carriers in degraded SrTiO3 is studied by using impedance spectroscopy (IS) and electron energy loss spectroscopy (EELS). Impedance response from the degraded crystal is fitted with a modified three-element lumped circuit, and these three elements represent a leaky anode capacitance (p-type conducting), an intermediate region, and a leaky cathodic capacitance (n-type conducting) with additional elements (R-C) placed in the cathode region. The temperature dependence of an additional resistive element in the cathode region follows the relation of sigma = (A/T-1.5)exp(-E-a/KBT) with the activation energy of 0.096 eV, indicating the existence of a parallel conduction path via a non-adiabatic small polaron hopping mechanism in the degraded cathode region. The thickness of the n-type conducting region calculated from impedance data is in good agreement with oxygen vacancy profile directly measured by EELS. All the above data shows excellent self consistency and give insight to the important role of the polaron conductivity controlling the degradation behavior. (C) 2009 The Japan Society of Applied Physics