Templated grain growth of barium titanate-based perovskite single crystals

Single crystals of BaTiO3 were grown by templated grain growth (TGG). TGG involves contacting a single crystal "template" to a sintered polycrystalline matrix and then heating the assemblage to a temperature that promotes the migration of the single crystal boundary through the matrix. In this investigation mm-sized single crystals of BaTiO3 were produced by heating a 97% dense polycrystalline matrix with a Ba/Ti ratio <1.00 at temperatures above the eutectic temperature. The initial matrix composition was controlled by leaching different amounts of Ba from the matrix powder. Initial crystal growth rates were measured as a function of template orientation and matrix composition. Growth rates ranged from ∼590--790 mum/h, ∼180--350 mum/h, and ∼42--59 mum/h for {111}, {100}, and {110} oriented single crystal templates, respectively. The lower and higher limits to these ranges correspond to a matrix composition of 4.4 and 2.7 mol% excess Ti, respectively. Following formation of new facet planes for {111) and {100} templates, the growth rates then slowed appreciably. Exaggerated matrix grains were shown to influence the crystal growth rates at times greater than 10 hours at 1350°C. A diffusion-controlled model is proposed and correlated to the kinetic data as a function of template orientation and matrix composition.;The properties of mm-sized single crystals of BaTiO3 grown by TGG were examined. A dielectric constant, &egr;33T, of 260, polarizations of PR ∼ 12 muC/cm2 and Psat ∼ 21.5 muC/cm2, electromechanical coupling coefficients of k33 ∼ 0.51 and k31 ∼ 0.18, and piezoelectric coefficients of d33 ∼ 133 pC/N were achieved. It was found that entrapped porosity in the crystals made it difficult to fully pole the crystals.;Single crystals of Ba(ZrxT1-x)O3 were also grown by templated grain growth (TGG). Millimeter size single crystals of Ba(ZrxT1-x)O3 were produced by heating a BaTiO3 crystal in contact with a sintered polycrystalline matrix of 4.5, 5.0 or 8.5 mol% Zr-doped barium titanate for 30 hours at 1350°C. To facilitate boundary migration, the ceramic compact was made 3 mol% TiO 2 excess. The 4.5 and 5.0 mol% Zr-doped crystals were orthorhombic at room temperature, and for a pseudocubic (001) orientation, they showed remanent polarizations of 13 muC/cm2 and a high field d33 of 340--355 pC/N. The 8.5 mol% Zr-doped crystal (again oriented along the pseudocubic (001)) was rhombohedral at room temperature with a remanent polarization of 10 muC/cm2. A k33 value of 0.74 from resonance measurements was observed for the 4.5 mol% Zr-doped crystal.