Atomic Distribution and Morphology of Colloidal Particles Precursors of Bismuthinite

Abstract

Sols were prepared by mixing solutions of bismuth nitrate and thiourea in N,N-dimetilformamide. The corresponding colloidal particles were characterized by using X-ray powder diffraction, scanning and transmission electron microscopy, and quasielastic light scattering. Two size distributions of colloidal particles were found: one at 5 nm and another at 300 nm. The small colloidal particles were nanocapsules that aggregated to produce larger nanocapsules with diameters between 10 and 40 nm and a shell thickness of 5 nm, which aggregated to produce the large colloidal particles with the diameter of 300 nm. The capsule shells were noncrystalline, made of Bi-S atomic clusters that contained two bismuth and five sulfur atoms; the clusters formed chains and double Bi-S layers linked via metallic Bi-Bi bonds. Increasing the bismuth concentration in the sol induced the crystallization of the sample into the crystalline structure of bismuthinite. Aging the sol at different temperatures caused aggregation of the large nanocapsules into one-dimensional arrays that also interacted with each other, forming broccoli-like objects with dimensions of some micrometers. Aging the sol at 80 °C gave rise to a dendritic crystallization of bismuthinite.