Electrical conductivity of CaO doped 10NiO-NiFe_2O_4 composite ceramics

The effects of CaO content,in the range from 0% to 4%,and sintering temperature on the phase composition and electrical conductivity of CaO doped 10NiO-NiFe_2O_4 composite ceramics were studied.The results show that the composites consist of NiO phase and NiFe_2O_4 phase.There is an apparent oxygen absorbing and releasing behavior during the heating process in air for 10NiO-NiFe_2O_4 composites.The electrical conductivity of composites sintered at(1473K) markedly depends on the CaO content.As the CaO content is in the range from 0% to 1%,the conductivity increases firstly with the temperature increasing from room temperature to 773K,then abruptly decreases with one or two orders of magnitude at the temperature between 773K and 923K,and finally increases gently with the temperature increasing from 923K to(1233K).As the CaO content is in the range from 2% to 4%,the conductivity increases with the temperature increasing without a decreasing phenomenon.The maximum conductivity of 16.29S/cm at(1233K) is obtained for composites doped with 2%CaO,compared to the 1.03S/cm of the undoped composites.As the sintered temperature increases from(1473K) to(1573K),the electrical conductivity at(1233K)(increases) about 15 times for the undoped composites,compared to a slight increase for the 2%CaO doped composites.