Impact of thermobaric conditions on phase content, magnetic and electrical properties of the CoFe2O4 ceramics

The aim of these work was to investigate low temperature fast synthesis of cobalt spinel ferrite polycrystalline ceramics. The idea of combining high temperature and high pressures was in the possibility of a sharp decrease in the synthesis time by the lowering the threshold for activation of chemical interaction due to increasing the rate of diffusion kinetics. Test samples with 2–3 orders of magnitude less duration and reduced sintering temperature by 400º C comparing to conventional sintering were synthesized from initial oxides using solid state reactions method under high-pressure. The thermobaric conditions (combination of high temperatures and high pressures during synthesis) on phase content, structural properties, magnetic and electrical properties of the CoFe ₂O ₄ spinels were also investigated. The synthesis was performed at T = 800 °С under high pressures (P = 1–5 GPa) and duration of 1 min. Evolution of the phase composition, microstructure, magnetic and electrical properties of CoFe ₂O ₄ ceramics as function of the synthesis pressure was investigated using XRD, SEM, VSM and impedance spectroscopy respectively. Results of XRD demonstrate the formation spinel-like main phase (SG: Fd-3 m) with impurities. It was observed that average grain size decreased from 661 to 355 nm with P increasing from 1 till 5 GPa respectively. It was observed that the P increase induce the non-linear changes in magnetic properties. Thus, M _s decreased from 70,8–60 emu/g while H _c and M _r had a slight increasing trend with increase P from 1 till 5 GPa. CoFe ₂O ₄ samples that were produced under higher pressures demonstrated dramatically higher values of permittivity. The proposed method is perspective way for production of the high-density magnetic ceramics with significantly reduced sintering time in comparison with the traditional solid state reactions method. The modification of the proposed method for control phase composition and physical properties is the goal for further investigations.