Effects of temperature and Nd composition on non-linear transport properties in substituted Ce1-xNdxO2-δ cerium dioxides

Cerium dioxides doped or substituted by neodymium have been prepared using low- (320degreesC) and high-temperature (1600degreesC) processes. The Nd substituted ceria phase obtained at high temperature is a solid solution Ce(1-x)NdxO(2-delta) 0less than or equal toxless than or equal to0.30. Electrical impedance spectroscopy analyses have been performed in the temperature range 40-700degreesC. At temperatures above 400degreesC, Nyquist representations allow to separate three signals corresponding to bulk, grain boundary and electrode responses. Non-linear variations of the resistance and the capacitance as functions of temperature and composition x are observed. In the case of grain boundary and electrode interface signals, constant phase elements with non-integer exponent n have been used to represent the equivalent circuits. For each contribution, the conductance strongly increases then reaches a limit value, above x = 0.10. When composition x increases, the condensation of Nd-vacancy defect clusters might be at the origin of the non-linear evolution of the conductance. Bulk and grain boundary conductions present different activation energies (0.7 and 1.3 eV). (C) 2003 Elsevier Inc. All rights reserved.