Electrical Conductivity and Thermoelectric Power of La2NiO4+δ

The electrical conductivity, Seebeck coefficient, and thermal chemical expansion properties of La2NiO4+delta were measured as a function of temperature and oxygen partial pressure (pO(2)). The electronic conductivity was analyzed in relation to the thermoelectric power (thermopower) data to elucidate the positive deviation of the activity coefficient of hole on the basis of the delocalized electron model by using the Joyce-Dixon approximation of the Fermi-Dirac integral from the partition function in the quasi-free-particle approximation with the regular solution model. The electrical conductivity and thermopower vs oxygen activity were all explained consistently in the logical frame of the degenerate p-type conductor across the entire experimental range investigated. Like other K2NiF4-type oxides, the chemical diffusion coefficient was slightly higher than the surface exchange coefficient, suggesting the need for further work to enhance the sluggish surface exchange kinetics of oxygen. The best-estimated mobility values were in reasonable agreement with the reported values and the very weak temperature dependence of hole mobility suggested a band conduction. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3559186] All rights reserved.