Functional properties of percolative CoFe^sub 2^O^sub 4^-PbTiO^sub 3^ composite ceramics

The structural, microstructural, electrical and magnetic characteristics of CoFe2O4-PbTiO3 composite ceramics with various amounts of magnetic phase are reported. The magnetization as a function of magnetic field and temperature showed a “dilution effect” when decreasing the ferrite amount, while the magnetic Curie temperature remains in the range of about 750 K for all the compositions, with small shifts due to the possible doping. The maximum value of magnetostriction response of 122 ppm, was obtained for the composition with 85% amount of ferrite at a field of 8 kG. The variation of dielectric properties with frequency and temperature in the range of (300–800)K is characterised by a frequency independent peak derived from the ferroelectric-to-paraelectric phase transition of PbTiO3 component and two frequency dependent thermally activated relaxations: one in the range of (300÷420)K with an activation energy of 0.5–0.6eV and one in the paraelectric state at (420÷650)K, with an activation energy of ∼1.2÷1.4eV which were described in terms of charge defects in the composite system