Multi-phase coexistence in yttrium-substituted Ba0.9Ca0.1Zr0.07Ti0.93O3 lead-free piezoceramics

Abstract

Lead-free Ba0.9Ca0.1Zr0.07Ti0.93O3 + xY2O3(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared following conventional solid state reaction route. The average grain size of the ceramics diminishes with the addition of an appreciable amount of Y3+. All the prepared samples show frequency dispersion at lower temperatures and are relaxors. The ceramic composition with x = 0.02 was found to lie at the multi-phase coexistence region at room temperature, comprising of orthorhombic and tetragonal phases. The Curie temperature (Tc) of this sample is 82 °C, a significant 10 °C rise from that of the undoped sample. The dielectric constant at room temperature (εrt), dielectric constant at Curie temperature (εm), remnant polarization (Pr) and coercive field (Ec) were also found to be optimum for this particular composition, with εrt = 2400, εm = 4340, Pr = 6.75 μC/cm2, Ec = 4.21 kV/cm. The piezoelectric charge coefficient (d33) and electromechanical coupling coefficient (kp) were found to be optimized for the ceramics with x = 0.02 mol% yttrium, poled around curie temperature with the values d33 = 204 pC/N and kp = 30%. The study reveals that an optimum amount of Y3+ in Ba0.9Ca0.1Zr0.07Ti0.93O3 can lead to high density with low porosity, large crystallite size and the multi-phase coexistence thereby enhancing the dielectric, ferroelectric and piezoelectric properties of the ceramics.