Small-polaron mobility in nonstoichiometric cerium dioxide

Abstract

The high temperature drift mobility (ad) of charge carriers in nonstoichiometric cerium dioxide (CeOz_,X) has been calculated by combining the electrical conductivity and nonstoichiomet~ data on the basis of the oxygen vacancy model with correct ionization state. The electrical conductivity was measured by a four-probe d.c. technique and the nonstoichiometry by thermogravimetric analysis. The dilute solution model of the point defects is valid up to x = 0.03. From the magnitude of pd and its temperature dependence, the charge carriers in CeO,_, are proposed to be small-poiarons formed by localization of electrons at cerium sites and the charge transport process is proposed to occur by a hopping mechanism. The observed temperature dependence of s,+ is in accord with that derived by Holstein and Friedman for small-poiaron transport by the hopping mechanism. The activation energy of mobility is found to increase with increasing x as expected for the hopping model.

Electronic and Ionic Transport in Ce0.8PrxTb0.2−xO2−δand Evaluation of Performance as Oxygen Permeation Membranes

“…These values are in good agreement with literature values for small polaron migration in other ceria systems. 19,49,50 The pre-exponential factors show a decreasing tendency with decreasing Pr/Tb ratio. The compound with [Pr] = 0.15 does not follow this trend.…”

Electrical Transport Properties of Polycrystalline Chromium Vanadate

“…Small polarons conduct either via a hopping mechanism or by a band mechanism. In the temperature region 300-750 K, small polaron band conduction cannot take place [17], Therefore the only possibility left is conduction via a small polaron hopping mechanism in which the charge carrier mobility increases exponentially with temperature. In this compound, the charge carrier mobility increases with temperature as evidenced by the increase in the thermo-electric power with temperature below 750 K. It is concluded that the conduction in the low temperature region is due to transfer of small polarons from the ions of chromium in different valence states, e.g.…”

Sub-nA spatially resolved conductivity profiling of surface and interface defects in ceria films

“…Investigations into electronic conductivity in CeO 2−x with varying x values show that conductivity is related to the departure from stoichiometry 11 and an important point to note is that in addition to decreasing defect concentrations, increasing defect numbers can also reduce conductivity when increased past a certain threshold. 36 As noted by the authors, this issue could 2015) arise for a number of reasons such as defect interactions, localized electrons repelling one another, and a lack of suitable hopping steps for the polaron (Ce 4+ ions are required). Therefore, regions of particularly high or particularly low defect concentrations are expected to be poor electronic conductors in a polaron-hopping regime.…”