GROWTH OF NICKEL ALUMINATE SINGLE-CRYSTALS BY THE FLOATING-ZONE METHOD

Nickel aluminate (NiAl2O4) single crystals were successfully grown by a floating zone method using a single ellipsoid image furnace. Single crystal growth was attempted in an oxygen atmosphere by using a xenon are lamp and also a halogen lamp. A single crystal, 5 cm long and 5 mm in diameter, was successfully obtained only by using the halogen lamp with a growth rate of 5 mm/h. The growth direction was determined to be [100] and the composition of the single crystal was found to be Ni0.91Al2.06O4, Significant differences in composition for different growth rates of 2.5, 5 an 10 mm/h were not observed. NiO evaporation leads to the growth of Ni-poor single crystals. Addition of excess NiO (5 and 10 mol%) to the starting material increases the Ni content in the NiAl2O4 single crystal. The influence of temperature gradient and growth rate on the stability of the growth and composition of the single crystals, are discussed.