Surfactant-assisted solvothermal synthesis of single-crystalline ternary Bi–Sb–Te hexagonal nanoplates
Introduction
Bi2Te3-based alloy is known as the best thermoelectric materials currently available for application near room temperature. Recently, significant thermoelectric properties improvement in the bulk materials has been achieved by creating nanograins and nonostructures in the grains by a combination of nanopowder preparation and sintering technique [1], [2], [3], [4], [5], [6], [7], [8]. The nanoparticles are produced by many methods, such as hydro/solvothermal methods [3], [4], spin melting [1], ball milling [2], [5], [8]. The sintering technique in the materials mainly involves the hot pressing [2], [3], [4] and spark plasma sintering [5], [7], [8]. The resultant properties of the bulk materials are related to the size and morphology of nanograins and nonostructures in the grains [9]. Therefore, the regulation of size and morphology for ternary Bi2Te3-based nanocrystal is of great importance for the development of higher efficiency devices of thermoelectric application. Moreover, compared with the large quantities reports about regulating the morphology of binary A2VB3VI compounds, the study about the controlling growth of the ternary (Bi,Sb)2Te3 or Bi2(Te,Se)3 nanocrystals is limited.
Among current methods for the synthesis of nanostructure thermoelectric materials, the chemical routes have the advantages of low synthesis temperature, flexible controllability and fine grain sizes in comparison with those traditional metallurgical processes. The binary Bi2Te3 nanostructure with various morphologies such as nanoparticles [10], [11], [12], nanosheets [13], nanowires [14], [15], hollow nanospheres [16], nanotubes [17] and nanoplates [18], [19] has been prepared by solvo/hydrothermal method, wet chemical reactions. Bi2(Te,Se)3 nanoparticle [20], Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 nanocrystals [21], Bi2Te2Se and BiSbTe3 hexagonal nanoplatelets are also synthesized by the chemical ways [22]. In this work, the morphology of ternary (Bi,Sb)2Te3 nanocrystal is tried to regulate and control by the solvothermal route. Large scales of two-dimensional hexagonal Bi0.5Sb1.5Te3 nanoplates are fabricated. The product morphologies are controlled by changing the added quantities of surfactant CTAB and water/ethanol volume ratio. Finally, the surfactant oriented growth mechanism for the hexagonally nanoplates of ternary (Bi,Sb)2Te3 is proposed.
Section snippets
Experimental details
All the regents were bought from commercial channels and used without further purification. The typical synthesis procedure is as follows: different quantities of hexadecyltrimethylammonium bromide (CTAB) were dissolved into a 40 mL mixture solution of water and ethanol volume ratio (1:1, 1:2, 1:4, 1:6), followed by the addition of BiCl3 (0.5 mol/l), SbCl3 (1.5 mol/l) and Te (3 mol/l) and NaOH (0.27 g) and NaBH4 (8 mol/l). The resulting precursor suspension was stirred vigorously for 0.5 h and then
Results and discussion
Fig. 1 shows the morphologies of the as-prepared ternary (Bi,Sb)2Te3 compounds in the various solvents and surfactant concentration. It can be clearly seen that the morphologies of the obtained product are gradually from nanoparticles to hexagonally shaped nanoplates with the CTAB concentration and the ethanol volume ratio increasing.
The XRD pattern of (Bi,Sb)2Te3 nanocrystal synthesized in the water and ethanol volume ratio of 1:6 with 0.2 g CTAB (the same reaction condition as in Fig. 1c) is
Conclusions
In summary, Bi0.5Sb1.5Te3 single-crystalline nanoplates have been synthesized in large scale via a simple solvothermal method assisted by surfactant CTAB. The size of nanoplates is 100–450 nm in edge length and 30–90 nm in thickness. TEM and SAED patterns show that the as-prepared nanoplate is highly crystallized and free from dislocation and stacking faults. The product morphologies can be controlled by changing the added content of CTAB and water/ethanol volume ratio. The surfactant oriented
Acknowledgements
This work was supported by the National Natural Science Youth Foundation of China (No. 50701031) and by Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0739).
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