Enhancing thermoelectric behavior of Bismuth Selenide crystal via substitution of Sulfur and Tellurium

Sulfur and Tellurium substituted Bismuth Selenide (Bi 2 Se 3-x-y S x Te y, x = y = 0, 0.1, 0.15, 0.2) quaternary alloy crystals were synthesized by using vertical Bridgman technique. Energy dispersive analysis of X-rays confirmed elemental composition and purity of the grown crystals. Field emission scanning electron microscopy showed that the growth of crystals has occurred by layer growth mechanism. Rhombohedral crystal structure is validated through analysis of powder X-ray diffraction pattern. Thermoelectric parameters such as electrical conductivity, Seebeck coefficient and thermal conductivity were calculated from 303 K to 773 K and from that power factor as well as figure of merit have been determined for all grown crystals. Electrical conductivity significantly increased due to Sulfur and Tellurium incorporation and maximum value obtained is 147.72 S/cm at 503 K for Bi 2 Se 2.6 S 0.2 Te 0.2 . Seebeck coefficient and thermal conductivity showed decrement with incorporation of Sulfur and Tellurium. Reduction in thermal conductivity and enhancement in electrical conductivity resulted in the improvement of figure of merit. Sulfur and Tellurium substitution showed considerable improvement in ZT from 0.31 (533 K) for pristine Bi 2 Se 3 to 1.28 (523 K) for Bi 2 Se 2.6 S 0.2 Te 0.2.