Electrical Conductivity of the Spinel CoFe2O4 Solid Solution

摘要

Spinel CoFe2O4 solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and メ-Fe2O3 polycrystalline powders. The spinel structures of the CoFe2O4 solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched CoFe2O4 had a partially inversed spinel structure (Co0.23Fe0.77) < Co0.77Fe1.23 > O4, while the slowly cooled CoFe2O4 was completely inversed spinel (Co0.04Fe0.96) < Co0.96Fe1.04 > O4. The CoFe2O4 specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to 900∩ under oxygen partial pressures from 10-3 to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that Co2+ ℃ CO3+ + e- and Fe2+ ￡ Fe3+ + e- are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.