Facile hydrothermal synthesis and formation mechanisms of Bi2Te3, Sb2Te3 and Bi2Te3-Sb2Te3 nanowires

A facile and scalable glucose-assisted hydrothermalmethod has been established for the fabrication of Bi2Te3, Sb2Te3 and Bi2Te3-Sb2Te3 nanowires in high yield. PH additives, such as HCl and NaOH, play crucial roles for the fabrication of Bi2Te3, Sb2Te3 and Bi2Te3-Sb2Te3 nanowires. It is suggested that fine Te nanowires are initially formed and they serve as templates for the fabrication of telluride nanowires. Bi2Te3 nanowires are obtained by direct one-step hydrothermal synthesis under acidic conditions when HCl is used as the pH additive. The as-prepared Bi2Te3 nanowires have different wire axes that can be parallel or perpendicular to the [001] direction. Two different mechanisms, i.e., structural preference growth mechanism and coherent growth mechanism are suggested for the formation of Bi2Te3 nanowires. A single phase of Sb2Te3 cannot be obtained under acidic conditions due to the slow kinetics of the reduction reaction even at elevated reaction temperatures. A two-step synthesis is proposed for the fabrication of Sb2Te3 and Bi2Te3-Sb2Te3 nanowires, where Te nanowires are first formed with a HCl additive and Sb2Te3 and Bi2Te3-Sb2Te3 nanowires are then fabricated with a NaOH additive. Besides the enhanced phonon scattering and quantum confinement effect, the structure and composition fluctuation in the Bi2Te3-Sb2Te3 nanowires may further adjust the energy band structure and improve the thermoelectric properties.