Temperature and frequency dependence of dielectric, electrical, and thermistor properties in Gd-doped CoFe2O4

Abstract

This study investigates the electrical transport properties of gadolinium-doped cobalt ferrite (Gd-doped CoFe₂O₄) which is prepared by a high-temperature solid-state synthesis method. The study mainly focuses on the sensitivity of the material for different in temperature and frequency, exploring its potential application as a negative temperature coefficient (NTC) thermistor. X-ray diffraction analysis is used to verify the crystal structure and phase purity. Scanning electron microscopy (SEM) was used to characterize the surface microstructure. Particle size distribution analysis revealed that increasing the gadolinium (Gd) doping concentration has resulted in a decrease in average grain size. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the chemical composition of the Gd-doped cobalt ferrite (CoFe₂O₄) compounds. The dielectric properties of these compounds were examined as functions of temperature and frequency. The impact of grains on the overall electrical response of all the prepared samples was observed by analyzing the Nyquist (Cole-Cole) plots at various temperatures. The NTCR characteristics of the prepared materials were determined from the temperature response of DC conductivity. The grain resistance at various temperatures is used to evaluate the thermistor parameters by considering the strong temperature dependence of resistivity. This indicates the potential use of grain resistance in thermistor-based devices. The frequency-dependent conductivity agrees well with Jonscher’s proposed universal power law. Temperature-dependent spectroscopic plots of the conductivity provide the activation energy, which exhibits that the charge carriers influence the transport characteristics of the compound.