Understanding the microstructure of complex crystal structures is critical for controlling material properties in next-generation devices. Synthetic reports of twinning in bulk and nanostructured crystals with detailed crystallographic characterization are integral for advancing systematic studies of twinning phenomena. Herein, we report a synthetic route to controllably twinned olivine nanoparticles. Microstructural characterization of Fe2GeS4 nanoparticles via electron microscopy (imaging, diffraction, and crystallographic analysis) demonstrates the formation of triplets of twins, or trillings. We establish synthetic control over the particle crystallinity and crystal growth. We describe the geometrical basis for twin formation, hexagonal pseudosymmetry of the orthorhombic lattice, and rank all of the reported olivine compounds according to this favorability to form twins. The work in this study highlights an area ripe for future exploration with respect to the advancement of solution-phase synthetic approaches that can control microstructure in compositionally complex, technologically relevant structures. Finally, we discuss the potential implications for olivine properties and performance in various applications.
Keywords: crystal twinning; electron microscopy; nanoparticles; olivine; trillings.