Quaternary thermoelectric materials: Synthesis, microstructure and thermoelectric properties of the (Bi,Sb)2(Te,Se)3 alloys

High-quality quaternary Bi0.5Sb1.5Te3−xSex (BSTS) alloys with x = 0.3, 0.5 and 0.75 are successfully synthesized in 25 min by high pressure and high temperature (HPHT) method. Due to the effects of synthesis pressure and Se doping, the texture and microstructure exhibit abundant distorted layers and lattice defects. The unique triangular nanoplates can be obtained in the microstructures by HPHT method without any substrates, suggesting that Bi0.5Sb1.5Te3−xSex has a nature of the epitaxial growth. The thermoelectric transport properties are characterized in detail, revealing an evident correlation with the amount of Se doping. As a result, a maximum ZT value of 0.95 is achieved at 503 K from the as-prepared Bi0.5Sb1.5Te2.7Se0.3 alloys. Additionally, Raman spectra are conducted and then indicate that Se doping contents have an important influence on the lattice vibrations and lattice structures of quaternary (Bi,Sb)2(Te,Se)3 alloys.