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Defect thermodynamics and electrical properties of nanocrystalline oxides: pure and doped CeO2

1997; Elsevier BV; Volume: 9; Issue: 1-8 Linguagem: Inglês

10.1016/s0965-9773(97)00142-6

1872-9150

Yet‐Ming Chiang, Erin Lavik, Doughas A. Blom,

Electronic and Structural Properties of Oxides

Electrical characterization of fully-dense, nanocrystalline CeO2 (10 nm grain diameter) of undoped and Gd-doped compositions illustrates the influence of size scale on defect formation thermodynamics and transport properties. In undoped n-CeO2, the heat of reduction is less than one-half the value for conventional polycrystals and single crystals, and the electronic conductivity is correspondingly enhanced. Preferential oxygen vacancy formation at grain boundary sites is indicated. Ionically conducting n-Ce0.74Gd0.26O1.87 exhibits no conductivity enhancement, indicating that oxygen vacancy conductivity is not significantly increased along grain boundaries. Lightly-doped Ce0.9846Gd0.0154O2-x, which is normally an ionic conductor, becomes electronically conducting at nanocrystalline grain size. In all compositions, reduction of grain size also results in a lower resistance per grain boundary, which is attributed to size-dependent grain boundary segregation. The results show that size reduction to the nanometer scale provides a new way to control stoichiometry and electronic conductivity in semiconducting oxides.