A tri-phase percolative ceramic composite with high initial permeability and composition-independent giant permittivity

Abstract

The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO₃ (BTO)/Ni_0.5Zn_0.5Fe₂O₄ (NZFO)/BaFe₁₂O₁₉ (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process of sol–gel and self-combustion methods. The content of the BFO phase could be tuned conveniently by controlling the preparation conditions. The as-prepared BTO/NZFO/BFO tri-phase composite exhibited unprecedented stable dielectric properties that were distinct from those of conventional percolative composites above the percolation threshold due to the existence of a third phase. When the volume fraction of the NZFO phase exceeds 55%, the electrical conductivity and effective permittivity of the composite remain at a stable value of about 10⁻⁵ S cm⁻¹ and 10 000, respectively, which is almost independent of the composition. Such behavior is the result of the synergistic control effect of the percolation effect and specific phase composition in the system. It is evident that the stability of the dielectric properties of the composite is chiefly contributed by the introduction of the BFO phase. Meanwhile, the composite exhibited a relatively high permeability of ∼17 with 90% NZFO loading, and its saturated magnetization is larger than 73 emu g⁻¹, approximately 95% of the pure NZFO phase. The finding of our BTO/NZFO/BFO tri-phase ceramic composite with stable giant permittivity and extremely high permeability paves a new way to solve the difficulty of property instability above the percolation threshold in the utilization of percolative materials.