The growth of ferroelectric single crystal Sr2Nb2O7 by means of the floating zone technique

A floating zone technique has been used for the synthesis of single crystals of new ferroelectric materials. The molten zone of the material was formed by radiant heating using a halogen lamp. The lamp and the ceramic rod of the material were arranged to be adjacent foci of an elliptical reflector. The temperature fluctuations in the molten zone are reduced by using a constant power supply to the lamp. Contamination by impurities is minimal. Sr2Nb2O7 a newly-discovered ferroelectric, with m.p. 1700 C, was synthesized and grown as pale yellow transparent single crystals. The colour of these crystals faded on annealing at 1000°C for 2 hr. It is important that the starting material be stoichiometric to achieve good crystals. The composition of one of the crystals obtained was found to be Sr2.00±0.03Nb2.05±0.02O7. Natural cleavage occurs parallel to the b-plane. The Laue patterns, conoscopic and orthoscopic figures, and the electromechanical coupling factor k33 before and after poling, were observed in order to determine the homogenity in the crystal. No internal stress or twins were found. The value of k33 before poling (0.26) was the same as that after poling. The single crystals appear to be homogeneous single domain material.