Material’s Design beyond Lateral Attachment: Twin-Controlled Spatial Branching of Rutile TiO2

Abstract

Crystallization by oriented attachment (OA) is changing our conventional understanding of crystal growth and holds promise for creative design of diverse hierarchic mesostructures. To achieve angular branching of mesostructures, we can exploit twinning. Here we show that in rutile TiO2 twin-based OA can be realized in a solvothermal process from Ti(IV)-butoxide under mild acidic conditions that favor precipitation of rutile with short-prismatic morphology. The aspect ratio of precipitated nanocrystals was shown to decrease linearly with the acidity of the medium; i.e., lower it is, higher is the affinity for twin OA. For a given aspect ratio, the frequency of twinning is controlled by precursor concentration. Through the control of lateral {110} and twin {101} OA in rutile, we are able to generate diverse fractal-like multiply twinned inorganic mesostructures for nanotechnology applications. To quantify branching, we define a morphology factor, fm, a new generally applicable criterion, which provides a qu...