Monitoring the multiphasic evolution of bismuth telluride nanoplatelets

Adjusting the synthetic route to control the shape, composition, and crystal structure of nanostructured topological insulators (TIs) is a challenge in the realization of TI systems with specific functionalities. Here, we report probing the multiphasic evolution of Bi2Te3 nanoplatelets primarily using microscopic, elemental and crystallographic methods. An evolution model is proposed along which the nanoplatelets undergo compositional and morphological changes. These changes have a pronounced impact on the electronic and thermoelectric properties of the initial, intermediate, and final stages of the model. The materials are synthesized via a solvothermal method, which, depending on the control of the precursors' relative concentrations, leads to multiphasic materials ranging from stoichiometric Bi2Te3 nanoplatelets to Bi4Te3 and BiTe. A twin plane model appears to explain adequately the successive formation of different Bi-rich phases, allowing control of the morphological and electronic properties of the yield. Specifically, the initial formation of Bi-rich triangular nanoplatelets triggers the generation of additional twin planes and subsequently leads to the ultimate 2D growth of hexagonal bismuth telluride nanoplatelets. The findings of this study pave the way towards engineering novel nanostructured Bi-Te topological compounds with tailored properties.