Growth of (1 - X)NaNbO₃-xBaTiO₃ single crystals by slow-cooling and flux methods

(1 - x)NaNbO₃-xBaTiO₃ single crystals were grown by slow-cooling and flux methods. In the slow-cooling method, 0.88NaNbO ₃-0.12BaTiO₃ powder was melted in a platinum crucible at 1500 °C and cooled down to 1000 °C. Slow cooling at less than 21 °C/h led to a bulky single crystal, and the BaTiO₃/NaNbO ₃ ratio was graded inside the single crystal as expected from the phase diagram. Further slow cooling at 5 °C/h with the aim of improving the compositional uniformity increased the level of contamination of platinum in the single crystals from the crucible. Cuboidal single crystals with a (100) facet were grown in Na₂B₄O₇ flux through a cooling process from 1200 to 1000 °C at 1 °C/h. There was no compositional gradient inside the cuboidal crystals, and the BaTiO₃ content of the single crystals remained within 2-3% irrespective of the raw powder/flux ratio and the BaTiO₃ composition in the raw powder. The obtained single crystals were orthorhombic ferroelectrics with a phase transition temperature of 310-330 °C.