GROWTH OF UNCRACKED BARIUM-SODIUM NIOBATE CRYSTALS

It is known that cracking occurs in Barium-Sodium Niobate, Ba 4 Na 2 Nb 10O30 (BNN), during Czochralski (cz) growth. This is due mainly to lattice distortions associated with the ferroelectric phase transition. We have studied the cz crystal growth condition for BNN without cracking, and found that high quality single crystals of BNN without cracking can be grown by using Gd-doped starting melt, i.e., Ba 4 Na 2 Nb 10O30-Ba3NaGdNb10O30 solid solution. In order to confirm the effect of Gd doping on the crystalline quality, Gd concentrations were measured by ICP for both the cz single crystal sample and the starting powder material. Gadlinium concentration in the as-grown crystal was about 0.195 mol %, nearly the same as that (2.0 mol %) in the starting material. Dielectric constant along c-axis, ε33, was measured at temperatures from 300 K to 870 K. The experimental result revealed that ε33 of the single crystal is about two times larger than that of BNN single crystal without Gd impurity in the temperature range from 300 K to 650 K.