NSF Award
8760821
In this project, a general approach for the preparation of beta-barium borate and other similarly growth-constrained crystalline materials is investigated. The approach is a modification of the Heat Exchanger Method (HEM) of crystal growth. The modification imposes 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 the mass transport mechanism. The method allows crystal growth to proceed without the complications currently encountered in high temperature solution growth by slow cooling. Beta-barium borate, a non-linear optical material, transforms to the non-optically active centrosymmetric alpha-phase at 925 degrees Celsius, before melting at 1105 degrees Celsius. The non-reversible nature of this transformation imposes severe restrictions on the growth method and precludes single crystal growth directly from the melt.
