<i>In Situ</i> TEM and AFM Investigation of Morphological Controls during the Growth of Single Crystal BaWO₄

Barium tungstate (BaWO₄) is a widely investigated inorganic optical material due to its attractive emission properties. Because those properties strongly depend on crystal structure and morphology, numerous approaches to controlling growth have been pursued. However, an understanding of the growth mechanisms that lead to the wide range of morphologies obtained to date is largely lacking, and most attempts to develop that understanding have been based on post-growth analyses. Significantly, such analyses have led to the conclusion that certain BaWO₄ crystal morphologies result from a nonclassical growth process of oriented attachment. In this work, we systematically varied the morphology of BaWO₄ crystals by adjusting the relative concentrations of solute, water, and ethanol. We then explored the growth mechanism leading to the observed range of morphologies through <i>in situ</i> TEM and <i>in situ</i> AFM. We find that even the most complex BaWO₄ morphologies occur through purely classical growth mechanisms largely controlled by the content of solute and ethanol. The latter acts as an impurity to poison growth at low concentrations and low solute levels, but leads to development of growth instabilities and eventual dendritic growth at high alcohol and moderate solute concentrations by driving up the supersaturation. These findings also highlight the necessity of <i>in situ</i> experiments to interpret <i>ex situ</i> observations of crystal growth and decipher the controlling mechanisms