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Diffusion; Conductivity relaxation measurements; Cr-doping; Polycrystalline NiO
Abstract:
Conductivity relaxation measurements were performed to investigate transport properties of polycrystalline undoped and Cr-doped NiO ceramic samples, Ni1-xCrxO (x = 0.1, 0.3, 1%). Conductivity (sigma) and chemical diffusion coefficient (D-delta) values were found to depend in a nontrivial way on the Cr content, thermal history and grain size of the samples. Post-annealed 0.1% Cr-doped NiO showed a significant decrease in sigma and an increase in D-delta. A further increase in Cr content caused a decrease of the chemical diffusion coefficient, which we ascribe to an inhomogeneous Cr distribution. The Cr segregation and the formation of undesired NiCr2O4 spinel precipitations are detected by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) indicating a much lower solubility limit for Cr than reported in literature. At 700 degrees C, the achievable increase of the chemical diffusion coefficient by Cr-doping exceeds an order of magnitude.
