LAUSR

We demonstrate that the anion composition of ternary silver bromoiodide, AgBr1–xIx, nanocrystals determines their shape through the introduction of twin defects as the nanocrystals are made more iodide-rich. AgBr1–xIx nanocrystals grow as single-phase, solid solutions with the rock salt crystal structure for anions compositions ranging from 0 ≤ x < 0.38. With increasing iodide content, the morphology of the nanocrystals evolves from cubic to truncated cubic to hexagonal prismatic. Structural characterization indicates the cubic nanocrystals are bound by {100} facets, whereas the hexagonal platelet nanocrystals possess {111} facets as their top and bottom surfaces. Calculations based on first-principles density functional theory show that iodide substitution in AgBr stabilizes {111} surfaces and that twin defects parallel to these surfaces possess a low formation energy. Our experimental observations and calculations are consistent with a growth model in which the presence of multiple twin defects parallel...