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, 0.88NaNbO3–0.12BaTiO3 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/NaNbO3 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.