Directing Growth of Compact Spherulites from Spherical to Complex Morphologies

Spherulites are polycrystalline architectures defined by their radial internal alignment, often forming spherical morphologies. Unlike faceted single crystals, their nonfaceted growth enables a decoupling of the external morphology from the internal crystallographic symmetry, offering a promising route to complex and radially aligned crystal shapes. However, the growth of compact spherulites remains uncommon, poorly understood, and largely limited to spherical shapes. Here, we precipitate strontium sulfate (SrSO4) in the presence of silica into compact hemispherical spherulites from solution and steer their morphology into nontrivial geometries. Our mechanistic studies reveal that after a nucleation burst, growth occurs via a diffusion-limited process and can be paused and resumed seamlessly due to the tunability of solution conditions. This tunability allows for size and morphology control, which we demonstrate with the templated fabrication of complex quarter-sphere, acorn, and interconnected network spherulitic shapes. These findings establish spherulitic growth as a versatile tool for building complex architectures, offering structural control beyond archetypical spherical forms and the limits imposed by crystallographic symmetry.