Phase transition induced morphotropic phase boundary behavior and the electric properties in strontium modulated Bi4.5Na0.5Ti4O15 lead-free ceramics

Abstract Lead-free (Bi0.5Na0.5)1-xSrxBi4Ti4O15 ceramics (x = 0–0.9) are fabricated by solid state reaction process. XRD analysis shows the symmetry divergence from tetragonal to orthorhombic phase accompanied by morphotropic phase boundary with increasing strontium content. Raman spectra confirm the incorporation of strontium into (Bi2.5Na0.5Ti4O13)2- layers. SEM graphs exhibit the typical plate-like morphology with regular variation of grain size and crystallization as strontium increases. Multistage ferroelectric transition is observed with x = 0.2–0.4. Piezoelectric performance measurements present the well thermal stability at x = 0.4. The dielectric properties display a shifting of Curie temperature towards low temperature with increasing strontium ions. It can be due to the crystal lattice distortion by larger radius of strontium and the increasing tolerance factor. ac conductivity and impedance measurements suggest that electron hopping mainly contributes to the low temperature region. Ionization conductivity by oxygen vacancy migration including first-ionization and double-ionization plays the dominating role in the middle and high temperature region. The controllable properties indicate the potential applications for electric devices of (Bi0.5Na0.5)1-xSrxBi4Ti4O15 ceramic.