Magnetoelectric composites of lead-free piezoelectrics and yttrium iron garnet: interfacial reactions and functional properties

Abstract

A wide range of magnetoelectric composites has been prepared: (100 − x) wt% FE + x wt% YIG (x = 30–70 in steps of 10 wt%), where YIG is yttrium iron garnet and FE is a lead-free ferroelectric material reported in the literature, namely lithium sodium potassium niobate ([Li0.06(Na0.52K0.48)]1.04NbO3, KLNN), modified sodium bismuth titanate ([96 mol.% Bi0.5(Na0.84K0.16)0.5TiO3 + 4 mol.% SrTiO3 + 0.2 wt% La2O3], BNT) or barium calcium zirconate titanate (Ba0.85Ca0.15Ti0.9Zr0.1O3, BCZT). The interfacial reactions and dielectric, piezoelectric, magnetic and magnetoelectric behaviors of the composites have been studied. The high-temperature calcination was found to yield the fergusonite-type impurity phase YNbO4 in KLNN-containing composites and the pyrochlore-like phase Y2Ti2O7 in BNT-containing ones. The BCZT-containing samples remain the only phase-pure materials after heat treatment. As a result, among the materials studied, the samples of (100 − x) wt% BCZT + x wt% YIG show the best magnetoelectric coupling coefficient ΔE/ΔH that reaches ~ 5 mV/(cm Oe) with x = 40. Despite showing significant piezoelectric response, the KLNN-containing ceramics exhibit ΔE/ΔH of 1.2 mV/(cm Oe) or less. The composites containing BNT show weak piezoelectric and almost zero ME response (ΔE/ΔH does not exceed 0.2 mV/(cm Oe)) due to the decomposition of ferroelectric phase caused by high-temperature interfacial reactions. The BCZT-containing composites appeared to be magnetically softer than KLNN-containing materials and magnetically harder than BNT-containing ones.