Grain boundary modulation improved thermal stability of high thermoelectric performance Mg3(Sb,Bi)2-based compounds

Mg 3 (Sb,Bi) 2 -based Zintl compounds are rising stars with superior features of high thermoelectric (TE) performance, nontoxicity and low cost. However, the poor thermodynamic stability hinders its practical application. Here, we propose a design strategy of modulating the local chemical composition with grain boundary (GB) phase guided by computational phase equilibrium diagrams. By in-situ constructing ZrSb 1- x second phase in the GB regions of Mg 3 (Sb,Bi) 2 -based compounds, the migration of Mg is blocked and the Mg deletion is depressed. Benefit from these, the driving force of Mg diffusion from matrix to GB and Mg migration along GBs is weakened, resulting in an improved thermal stability without degradation of electrical transport properties. The fabricated 8-pair TE module using GB modulated n-type Mg 3.1 Sb 1.5 Bi 0.49 Te 0.01 and p-type Ge 0.89 Cu 0.06 Sb 0.08 Te presents an efficiency of 8.9 % under the temperature difference of 450 K and shows excellent durability in the thermal cycling test. This study provides an effective strategy to improve thermal stability by constructing GB phase, and proves the feasibility of the practical application for Mg 3 Sb 2 -based TE modules.