Crystal Growth of NbC by Flux Method

Abstract

Single crystals of NbC were grown using Ni or Co metal, or Ni-Co alloy as a flux at soaking temperatures of 1600°-1900°C. When Ni flux was used, the crystal size increased with increasing temperature to 1800°C. Neither effect of keeping time (4-16h) nor cooling rate (0.7-7°C/min) on the crystal size at 1600°and 1700°C was found, while the longer keeping time and slower cooling rate at 1800°C resulted in the decrease of the crystals. The crystal of a maximum size of 1.8mm was grown at 20wt% NbC concentration when the melt was kept at 1800°C for 4h, and cooled at 7°C/min. The golden black cubic crystals obtained have a lattice constant of a₀=4.4695±0.0005Å, with nearly stoichiometric compositions The grown faces of the crystals were {100} family, and the dislocation density of 10⁸/cm² on these faces was measured for the crystals grown from 1800°C. The crystals grown after keeping at 1800°C for 4h contained Ni impurity of about 2900ppm, which then decreased to 600ppm in 16h. In the case of Co flux, the crystal size decreased with increasing temperature from 1600°to 1800°C, amaximum size being of 1.0mm. Neither effect of keeping time nor cooling rate on the crystal size was found at any temperature. The lattice constant and grown faces of the crystals were the same as the case of Ni flux. The crystals were found to contain a free carbon of 1wt% and Co impurity of 1250-7900ppm depending on the growth temperature of 1600°-1800°C. Ni-Co alloy flux with the wt% composition of Co/Ni=1/2 and 4/1 gave the crystals of 1.5 and 1.2mm size, respectively, at the NbC concentration of 15wt% and the growth temperature of 1700°C.