GROWTH OF BETA-BARIUM BORATE (BAB2O4) CRYSTALS VIA MASS TRANSPORT

BETA-BARIUM BORATE (BETA-BAB2O4), A NON-LINEAR OPTICAL MATERIAL, TRANSFORMS TO THE NON-OPTICALLY ACTIVE CENTROSYMMETRIC ALPHA-PHASE AT 925 DEGREES C, BEFORE MELTINGAT 1105 DEGREES C. THE NON-REVERSIBLE NATURE OF THIS TRANSFORMATION IMPOSES SEVERE RESTRICTIONS ON THE GROWTH METHOD AND PRECLUDES SINGLE CRYSTAL GROWTH DIRECTLY FROM THE MELT. A GENERAL APPROACH FOR THE PREPARATION OF BETA-BAB2O4 AND OTHER SIMILARLY GROWTH-CONSTRAINED CRYSTALLINE MATERIALS IS PROPOSED. THE PROPOSED APPROACH IS A MODIFICATION OF THE HEAT EXCHANGER METHOD (HEM(TM)) OF CRYSTAL GROWTH. THE MODIFICATION WILL IMPOSE THE NECESSARY PROCESS CONTROL TO CRYSTAL GROWTH FROM HIGH TEMPERATURE MOLTEN SALT SOLUTIONS. THE HEM ALLOWS A UNIQUE TEMPERATURE DISTRIBUTION TO BE CREATED WITHIN AN OTHERWISE "IDEAL" BLACK BODY, THEREBY ALLOWING MASS TRANSPORT FROM A NUTRIENT ZONE TO A GROWING CRYSTAL INTERFACE. THE TWO INDEPENDENTLY CONTROLLED PROCESS VARIABLES OPERATIVE IN HEM ALLOW OPTIMIZATION OF THEMASS TRANSPORT MECHANISM. THE PROPOSED METHOD WOULD ALLOW CRYSTAL GROWTH TO PROCEED WITHOUT THE COMPLICATIONS CURRENTLY ENCOUNTERED IN HIGH TEMPERATURE SOLUTION GROWTH BY SLOW COOLING.