A class of multiferroic, three-phase particulate composites of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer are investigated, in which a small volume fraction f of Tb–Dy–Fe alloy particles are dispersed in a PZT/polymer mixture. The measured dielectric, piezoelectric, and magnetoelectric properties demonstrate that a percolation transition occurs at f∼0.12 in the composites. When f is low (e.g., f<0.07), the composites exhibit piezoelectric and increasing magnetoelectric response. In the critical f range of 0.07<f<0.12, such piezo- and magnetoelectric responses sharply drop, and equal zero at the percolation threshold, above which the composite becomes a conductor and a magnetostrictive composite only.
We report on a systematic experimental investigation of a class of multiferroic, three-phase particulate composite of Tb–Dy–Fe alloy, lead–zirconate–titanate (PZT), and polymer, in which a small volume fraction f of Tb–Dy–Fe alloy particles without and with the particle surfaces modified by an inactive surfactant are dispersed in PZT/polymer mixture. The measured electrical properties demonstrate that a percolation transition occurs in the three-phase composite as in normal two-phase metal–insulator continuum media. Our piezoelectric measurements also show a percolation transition which provides an experimental test of the critical behavior of the piezoelectric composites with conductive fillers in the percolation regime. Accordingly, the multiferroic composite exhibits increasing magnetoelectric response in the low f range, but such magnetoelectric response sharply drops when f approaches the percolation threshold above which the composite becomes a conductive, magnetostrictive composite only. The inactive interface between the alloy particles and the PZT/polymer matrix induced by coating surfactant on the alloy particles produces a negative effect on the piezo- and magnetoelectric properties of the composite.
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