Effects of calcination temperature and flux doping on the microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites

The correlative influences of calcination temperature and Bi2O3 doping content on the microstructure and magnetic properties of the low-temperature-fired NiCuZn ferrites were investigated. For ferrites with relatively low calcination temperatures, such as 750 °C and 850 °C, Bi2O3 doping easily triggered inhomogeneous grain growth. Controlling the flux amount to lower than the 'critical' value, which triggered abnormal grain growth, was preferred to obtain good magnetic properties. For ferrites with relatively high calcination temperatures, such as 950 °C and 1050 °C, flux doping was not prone to stimulating abnormal grain growth. Thus, the optimum doping content could be added when the highest sintered density was detected. With excessive Bi2O3 concentrations, low-temperature-calcined ferrites could produce homogeneous microstructures with a relatively large average grain size. By contrast, high-temperature-calcined ferrites could form homogeneous microstructures with a relatively small average size, which favoured a high Q-factor and was more favourable for high frequency applications.