Seed-free solid-state crystal growth

What is it about?

Large Na0.5K0.5NbO3 (NKN) piezoelectric single crystals were obtained by seed-free solid-state crystal growth (SFSSCG) method, which is a traditional sintering grain growth process, with LiBiO3 used as a sintering aid. The largest dimension of the single crystals obtained was 11 × 9 × 3 mm3. In addition to the LiBiO3 doping content, temperature and time effect of the crystal growth process was systematically investigated and considered from the kinetics point of view. With the assistance of Avrami analysis, parameters relevant to the crystal growth process were determined. Laue diffraction and transmission electron microscopy suggested an orthorhombic symmetry for the single crystalline structure. Dielectric-frequency-temperature measurements revealed an orthorhombic-tetragonal and tetragonal-cubic phase transition at 155 °C and 405 °C, respectively, both of which are typical of first-order transitions, and have a well-defined thermal hysteresis. Rayleigh analysis was performed regarding to the extrinsic reversible and non-reversible piezoelectric properties, and the result suggested a dominant intrinsic reversible piezoelectric contribution of 91.5% under E0 = 1 kV/cm AC amplitude. Such a single crystal growth process route is low cost and a relative simple preparation process.

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Why is it important?

Large K0.5Na0.5NbO3 (NKN) lead-free piezoelectric single crystals were obtained by a seed-free solid-state crystal growth (SFSSCG) method by doping with a small amount of LiBiO3. The largest dimension of the single crystal is able to reach at 11 × 9 × 3 mm3. The NKN crystalline grains tend to form a self-assembled arrangement with a preferred orientation and grow by layer stacking along the growth orientation. A kinetic study was performed to better quantify the growth process. The rates of transformation are determined via an Avrami analysis. The single crystals are found to have a high-quality single-crystalline perovskite structure with an orthorhombic symmetry. The dielectric spectra suggest two first-order transition in the temperature range from 30~500 °C. And the electromechanical properties were further analyzed by Rayleigh analysis under low electric fields, where an averaged dinit ~ 205 pm/V is suggested from the intrinsic piezoelectric contribution.