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

Abstract

Mg₃(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 Mg₃(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_3.1Sb_1.5Bi_0.49Te_0.01 and p-type Ge_0.89Cu_0.06Sb_0.08Te 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 Mg₃Sb₂-based TE modules.