PHENOMENOLOGICAL INVESTIGATION OF INHOMOGENEITIES IN ND3-DOPED BA2NANB5O15 SINGLE-CRYSTAL FIBERS GROWN BY THE LASER-HEATED PEDESTAL GROWTH TECHNIQUE()

Inhomogeneities in Ba2NaNb5O15 (BNN) single-crystal fibres undoped or doped with 1-5 at% Nd3+ and grown by the laser-heated pedestal growth technique were investigated by energy-dispersive X-ray microprobe anal ysis (EDXA), second-harmonic generation (SHG) measurements and interfe rence contrast microscopy after chemical etching. The observed interna l morphology of BNN fibres was correlated to SHG and EDXA measurements and involves convective flow instabilities in the molten zone and pos sibly unsteady interface kinetics. From this study, it appears that fo r a doping concentration equal to 3 at% Nd3+,no growth striations nor any kind of inhomogeneity could be detected, indicating, as also shown by differential thermal analysis, that this mixture congruently melts , ensuring very-high-optical-quality crystals are obtained as no crack s nor microtwins are also present for this amount of neodymium. (C) 19 98 Chapman & Hall.