Multi-doping of Ni, Ti, and Zr at the Fe site enables multifunctional performance in BiFeO3-based ceramics

In this study, lead-free multiferroic thermistor materials based on BiFeO 3 were developed by co-doping with titanium, zirconium, and nickel. The compound BiFe 0.95 [(Ti 0.9 Zr 0.1 ) 0.5 Ni 0.5 ] 0.05 O 3 (BFTZNO) was synthesized via a standard solid-state reaction route. X-ray diffraction patterns and Raman spectra indicated a rhombohedral R3c symmetry in the BFTZNO sample, exhibiting considerable distortion of the FeO 6 octahedron alongside a minor Bi 25 FeO 40 secondary phase (∼1.27%). A distinct thermal anomaly observed at approximately 584 K in the differential scanning calorimetry (DSC) curve corresponds to the Néel temperature ( T N ), characterized by an endothermic peak. Analysis of the dielectric data using a modified Cole–Cole model revealed a pronounced change in the relaxation frequency near T N , indicating the influence of magnetic ordering on the electrical transport behavior. Future direct magnetic field-dependent measurements are essential to confirm the presence of magnetoelectric coupling. The study of dielectric properties supports the presence of a negative temperature coefficient of resistance ( NTCR )-type conduction mechanism, as confirmed by the extracted parameters: the thermistor constant ( B ) ranging from 4280 to 15150 K within the temperature range of 480–717 K, and the sensitivity index (α) varying from −1.76% K -1 to −3.05 % K -1 . Thermally stimulated polarization current ( TSPC ) and impedance measurements over ten thermal cycles up to 600 K demonstrated short-term stability. To validate long-term high-temperature reliability, an extended 120-hour continuous isothermal aging test was performed at 700 K. The BFTZNO ceramic exhibited a minimal relative resistance drift of less than 5%. These results establish BFTZNO as a stable and suitable for high-temperature NTC thermistors.