Studies on thermoelectric performance of pristine and Selenium alloyed Bismuth Sulfide crystals grown by vertical Bridgman technique

Abstract

By using Vertical Bridgman Technique (VBT), pure and Selenium alloyed Bismuth Sulfide crystals were grown. Effect of Selenium concentration on structural, electrical and thermal transport properties with respect to pristine crystal is thoroughly studied. Grown crystals were characterized by Energy Dispersive analysis of X-rays (EDAX), Field Emission Scanning Electron Microscopy (FE-SEM) and Powder X-ray Diffraction (PXRD) to confirm stoichiometry, surface morphology and structure respectively. Hall effect measurement is done to determine carrier concentration and mobility. Electrical conductivity, Seebeck coefficient and thermal conductivity were measured from 303K to 773K to study electrical and thermal transport mechanism. Electrical conductivity was increased from 3.84 S/cm to 33.34 S/cm with increasing Se concentration while Seebeck coefficient showed an opposite trend. Power factor also showed enhancement from 1.43 μW/cmK2 to 2.70 μW/cmK2 with Se substitution. Pristine S1 (Bi1.97S3.19) showed figure of merit ZT = 0.23 at 683K while maximum ZT = 0.54 at 733K was obtained for S4 (Bi1.97S2.88Se0.3) crystal. This study indicated that appropriate concentration of Selenium is beneficial to improve thermoelectric performance of Bismuth Sulfide.