24. Compositionally-induced shape-control in ternary silver halide nanocrystals

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Compositionally-induced twin defects control the shape of ternary silver halide nanocrystals.
B. Yin, X. Huang, R. Mishra, B. Sadtler. Chemistry of Materials 29, 1014 (2017).

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 to a {111} surface enhances lateral growth of the side facets and changes the nanocrystal shape. This new method to control nanoscale morphology based on anion composition provides a route to study structure–activity relationships in silver halide photocatalysts.

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Tags: 2017, R. Mishra, X. Huang