Insight into Nucleation and Growth of Bi2-xSbxTe3 (x=0-2) Nanoplatelets in Hydrothermal Synthesis

Controlled wet chemical synthesis of nanomaterials with tailored structures and properties, especially by hydrothermal/solvothermal methods, is difficult due to the complicated nucleation and growth processes. Therefore, it is important to gain a deeper understanding of the formation mechanisms involved in hydrothermal/solvothermal processes. In the present study, the formation mechanisms of Bi2-xSbxTe3 (x = 0-2) nanoplatelets under hydrothermal conditions are studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXRD). Synthesis using glucose as the reducing agent results in direct nucleation of Bi2Te3 from Bi and Te precursors without the presence of any intermediate products, and the nucleation stage is completed in only about 1 min at 250 degrees C. When Sb is added, the nucleation process for Bi2-xSbxTe3 becomes slower with increasing Sb content. Depending on the Sb content and reaction temperature, an intermediate product of elemental Te nanostructures forms, and it is found to direct the morphology of the final products. Within the duration of the measurements, Sb2Te3 only forms at relatively high reaction temperatures due to the slower kinetics of the reaction. A two-stage nucleation mechanism is found for the formation of the ternary BiSbTe3 with an initial nucleation stage of predominately Bi2Te3 followed by a second stage of slower nucleation and alloying process to BiSbTe3. Both the composition and reaction temperatures affect the crystallization kinetics and crystallite growth mechanisms during synthesis of Bi2-xSbxTe3 nanoplatelets.