Effects of the phosphorus-ion additive on the crystal habit of the emerald crystals grown from the V2O5-Li2O-P2O5 fluxes

Grown emerald crystals are all hexagonal prisms bounded by the c{0 0 0 1} and m{1 0 (1) over bar 0} faces irrespective of the concentration of P in the fluxes, indicating that P5+ ions little influence the appearance of the growth faces. Addition of an optimum P/(V + Li) molar ratio (similar to 6.9 x 10(-3)) of P suppresses nucleation and increases the yield, with the growth of the crystals having a mean volume three times that for the P-free flux. The most noteworthy effect is that the aspect ratio varies linearly from similar to 2 to similar to 10 with an increase in the concentration of P in the flux. The results of electron probe microanalysis reveal that P5+ ions are preferentially incorporated in the growth sectors with the m plane as the base. It thus follows that the incorporated P5+ ions suppress the growth rate of the m plane, and as a result, the growth of the c plane looks as if it is promoted. Wet analysis shows that with an increase in the concentration of P in the flux, the incorporated P5+ ions increase, and by contrast, the incorporated Li+ ions decrease. A reasonable explanation is that the Li+ ions located in the framework channels are removed by incorporation of P5+ ions. (C) 1998 Elsevier Science B.V. All rights reserved.