Study of the (Bi2Te3)0.25 (Sb2Te3)0.75 crystal structure modification with excess Te by AFM, EBSD and XRD and the figure of merit innovation

(Bi2Te3)0.25(Sb2Te3)0.75 solid solution is a p type thermoelectric compound with optimum efficiency among the (Bi2Te3)x (Sb2Te3)1-x compounds with variable x. Increment of Bi2Te3 segment in the Bi-Sb-Te system decrease in hole concentration, which result in carriers transport tuning, an increment of Seebeck coefficient and decrement of electrical and thermal conductivities. An excess of Tellurium up to 4wt% further elevates the thermoelectric efficiency (η), thus resulting in an increase in the figure of merit. Structural characterizations of this compound in the absence and presence of added Te were carried out by means of X-Ray diffraction measurement, electron backscattering diffraction and atomic force microscopy. Detailed analyses carriers transport behavior reveal the intrinsic structures formation and minimum defects during crystallization resulted in the excess of Te. The analysis show a maximum figure of merit at 3wt% excess Te.