Controlled growth, characterization and thermodynamic behavior of bismuth–tin nanostructures sheathed in carbon nanotubes

We report the controlled synthesis of bismuth–tin (Bi–Sn) nanostructures sheathed in graphitic shells that resemble carbon nanotubes (CNTs). Our approach is based on a simple catalytic chemical vapor deposition over a mixture of Bi2O3 and SnO2 supplied as starting materials. Shape control of the nanostructures strongly relies on the weight ratio of Bi2O3 and SnO2. Sheathed nanoparticles and nanorods are formed at SnO2 to Bi2O3 weight ratios of less than 4:1. They are composed of two separate crystals: rhombohedral Bi and tetragonal Sn19Bi crystals. On the other hand, the sheathed nanowires are formed at SnO2 to Bi2O3 weight ratios above 4:1. The nanowires have only tetragonal Sn19Bi structure with a diameter of approximately 100 nm. Elementary analyses support the core/shell heterostructure of the resulting products. A favorable temperature for the Sn-rich Sn19Bi nanowires is in the range of 700–800 °C, more specifically around 750 °C. Thermodynamic analysis reveals that the CNTs play a significant role in the protection of the Bi–Sn nanostructures during phase transition by temperature change. This simple and reproducible method may be extended to the fabrication of similar binary or ternary nanostructures.