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

Lead-free Ba0.9Ca0.1Zr0.07Ti0.93O3 + xY(2)O(3)(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 (T-c) of this sample is 82 degrees C, a significant 10 degrees C rise from that of the undoped sample. The dielectric constant at room temperature (epsilon(rt)), dielectric constant at Curie temperature (epsilon(m)), remnant polarization (P-r) and coercive field (E-c) were also found to be optimum for this particular composition, with epsilon(rt) = 2400, epsilon(m) = 4340, P-r = 6.75 mu C/cm(2), E-c = 4.21 kV/cm. The piezoelectric charge coefficient (d(33)) and electromechanical coupling coefficient (k(p)) were found to be optimized for the ceramics with x = 0.02 mol% yttrium, poled around curie temperature with the values d(33) = 204 pC/N and k(p) = 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.