Influence of annealing temperature on the structural, dielectric, and impedance properties of Sm and Co co-doped BiFeO₃ for advanced electronic and energy applications

Multiferroic bismuth ferrite promises transformative advances in nanoelectronics and energy devices, yet producing phase-pure, thermally stable nanoparticles, especially with dopants, remains a major challenge. In this work, samarium and cobalt co-doped BiFeO 3 nanoparticles were prepared using the sol-gel method by a citrate-ethylene glycol, with metal nitrate as precursors, and the annealing temperatures of 500 °C, 600 °C, 700 °C, and 800 °C were adopted to control the phase formation, microstructure, and electrical response to the nanoparticles annealing. X-ray diffraction confirmed that the structure of all annealed samples consists mainly of rhombohedral BiFeO 3 (R3c), and strong peaks are observed at 22.4–22.5°, ∼30.2°, 31.8–32.2°, ∼33.1°, ∼39.5°, ∼46.3° and ∼57.1° (2 θ ), and weak secondary peaks were more obvious at the lower annealing temperatures. With the increase of the annealing temperature, the crystallite size increased from 26.95 to 42.77 nm (with a slight decrease of crystallite size at the highest annealing temperature). In contrast, the lattice strain decreased from 0.46 to 0.30–0.33%, indicating the strain relaxation and improved crystallinity. SEM imaging shows agglomerated particles with pronounced grain growth, with the average particle size increasing from approximately 94 to approximately 209 nm as heating was increased from 500 to 800 °C, implying that several crystallites comprise each particle. Electrical properties were analyzed by impedance and dielectric spectroscopy from a wide frequency range at 50 °C to 300 °C. There is a strong dependence of the response on frequency: tan(δ), and ε″ are large at lower frequency and fall off slowly at higher frequency, which is compatible with interfacial/space-charge polarization and thermally activated hopping conduction. The impedance elements are used to support the above illustration, with the size of impedance (|Z|), the resistance (R), and the reactance (X) decreasing with the temperature and frequency. In addition, AC conductivity rises sharply with temperature (at 0.51 kHz from 6.36 × 10 −7 to 7.676 × 10 −2 Ω −1 m −1 between 50 °C and 300 °C) along with the decrease in resistivity, which is consistent with thermally activated charge transport. The results show that the annealing temperature has a great influence on the microstructure and the strain of the co-doped BiFeO 3 nano systems, which determines their dielectric relaxation, impedance, and transport properties. This study systematically investigates the effect of the annealing temperature on structural relaxation and transport of electric currents depending on temperature in Sm-Co co-doped BiFeO 3 nanoparticles. Co-doping with Sm and Co in combination with controlled annealing allows precise tuning of the crystal structure and the electrical transport of BiFeO 3 . This tunability renders the material suitable for use in energy-storage and energy-harvesting devices, transducers and actuators, sensors, RF/microwave components, magnetoelectric spintronic elements, and multistate memory and other advanced applications in nanoelectronics. • Predominantly rhombohedral (R3c) Sm-Co co-doped BiFeO 3 ; weak secondary phase at 500 ° C vanish after annealing. • Annealing relaxes lattice strain (0.46% - ∼0.30–0.33%), increases crystallite size (26.95–42.77 nm (up to 700 ° C , slight decrease at 800 ° C ). • SEM shows agglomerated nanoparticles with growth of at ∼94 - ∼209 nm at 500–800 ° C are observed. • Dielectric response is dispersive: ε′, ε″ and tan(δ) are high at low frequency and decreasing with higher frequency (50–300 ° C ). • Impedance confirm thermal activation. |Z|, R, and X decrease with temperature/frequency.