Bond Diversification and Grain Refinement Enabling High Thermoelectric and Robust Mechanical Performances in p-Type (Bi,Sb)2Te3

How to effectively reduce the thermal conductivity in bismuth telluride-based materials has become a hot topic in the field of thermoelectrics. In this work, we propose a method to increase the bond anharmonicity in p-type (Bi,Sb)2Te3 by increasing the bond diversity via alloying CuGaTe2. The solid solution of a trace amount of CuGaTe2 could change the chemical bonds in (Bi,Sb)2Te3 from unitary valent bonds to mixed (ionic and valent) bonds. The bond diversification then results in a significant reduction of the lattice thermal conductivity from 0.76 to 0.58 W m–1 K–1 at 300 K. A follow-up ball milling (BM) process not only optimized the hole concentration for an improved power factor but also realized grain refinement responsible for the enhanced compressing performance. Eventually, a high ZT peak of ∼1.4 at 423 K and an average ZT of ∼1.31 (300–473 K) was achieved in the composition of (Bi0.4Sb1.6Te2.997Cl0.007)0.995(CuGaTe2)0.005 after 6 h of ball milling. At the same time, the compressive strength was improved by ∼66% from 92 MPa of commercial zone-melting ingots to 153 MPa of the BM-6h sample above. The method used in this work might shed light on further research in bismuth tellurides and related thermoelectric systems.