Abstract
Cerium dioxides doped or substituted by neodymium have been prepared using low- (320°C) and high-temperature (1600°C) processes. The Nd substituted ceria phase obtained at high temperature is a solid solution Ce 1− x Nd x O 2− δ 0⩽ x⩽0.30. Electrical impedance spectroscopy analyses have been performed in the temperature range 40–700°C. At temperatures above 400°C, 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).
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