Preparation Of Bi₂Te₃ Nanoflakes With A Solvothermal Method And Doping Effect

The thermoelectric material is an important type of function materials, which can transform thermal energy to electric energy, and vice versa efficiently. Recently, more and more attention has been given to this material because it has a great deal of advantages, such as energy conservation, benign stability, non-pollution and long service life. At present, Bi2Te3-based series thermoelectric material as thermoelectric materials owns the best performance near greenhouse, but traditional Bi2Te3 thermoelectric materials lack of fine pyroelectricity; its supreme non-dimensional thermoelectric figure of merit (ZT) is about 1, far less than the ideal value corresponding to 3. For the past a few years, relevant theories and practices all indicated that the pyroelectricity could be markedly improved by thermoelectric materials with low-dimensional and nano sizes. The solvothermal method is a new type of method to prepare nanosize materials, whose advantages can be summed up as fellow:low synthesis temperature, short reaction time, high purity products and crystal particle of subsize. In the paper, this method is used to prepare Bi2Te3 nanoflakes. There fellows the main research contents:(1) The single phase Bi2Te3 hexagon nanoflakes were successfully prepared under alkaline environment, selecting and using glycol as solvent and PVPK-30 as additive, and the resultant temperature and time corresponded to 200℃and 260min. The structures, features and optical properties of the samples were characterized using XRD, SEM, PL and U-VAS.(2) The effect of synthesis temperature, reaction time and types of surface active agent were systematically studied on phase composition and microcosmic features. Further, the reaction processes of system and growing mechanism of the samples were analyzed, which indicated the reaction of resultant Bi2Te3 was mainly atomic reaction. Due to the peculiarities of Bi2Te3 itself, the growing direction of crystal nucleus was mainly perpendicular to c- axis, which was easy to form sheet structure. Under the action of PVPK-30 as surface active agent, the hexagon sheet structure of uniform size was finally addressed. (3) When low dimensional and nano materials were prepared, we try to dope rare earth elements on Bi sites. La, Y and Ce atoms were selected as doping element in single phase Bi2Te3 nanoflakes. The structure and features of the doped samples were checked by XRD, SEM and TEM. Our results indicated that Y atom cannot substitute Bi atom. Part micro-scrap matter was observed because of La-doping; however, the composition of the matter was still unclear. If the reaction time was improved to 280min, a small quantity of Ce atom was successfully doped, and the structure and features of Ce-doped samples was characterized.