Top-Seeded solution growth of lead zirconate titanate single crystals from a high temperature solution

Abstract

Lead zirconate titanate (PZT—Pb(Zr_XTi_1−X)O₃) single crystals were grown by the top-seeded solution growth (TSSG) method. Three solvent systems PbO-PbLiPO₄, PbO-Pb₂P₂O₇, and PbO-B₂O₃ were chosen for their low vapor pressures, but they also had high viscosity and molecular clusters that formed in the melt. To obtain crystals near the morphotropic phase boundary with X ≈ 0.52, melt compositions were formulated based on earlier phase diagram work with a low ratio of [ZrO₂]/([TiO₂] + [ZrO₂]) ∼0.1 in the melt. Liquid-phase epitaxy or top-seeded solution growth with various substrates was not effective because of the excessive lattice mismatch. Bootstrapping from seeding on a platinum wire to a PZT seed was necessary to grow large crystals.

To maintain a constant crystal composition, steady-state isothermal liquid-phase transport in a two-phase system was developed. This method relies on the phase diagram thermodynamic equilibrium between liquid and solid phases. The melt was equilibrated at the growth temperature with an excess of nutrients in the proper proportions to result in crystallites of the target composition precipitating on the bottom. In a negative vertical temperature gradient, this nutrient material dissolved and was transported to the cooler seed crystal at the top of the melt. This occurs at a constant average temperature to achieve a constant composition the same as the nutrient on the bottom.

The initial growth morphology of the crystals was a stepped surface, showing columnar growth of large macro-steps growing together trapping melt inclusions. This was improved through solvent choice, liquid-phase transport, and lower growth rates.