Establishing synthesis-composition-property relationships for enhanced and reproducible thermoelectric properties of MgAgSb

α-MgAgSb is a promising p-type thermoelectric (TE) with excellent performance from room temperature up to 300 °C with a figure of merit of zT max = 1.3. This makes MgAgSb a potential Te-free bismuth telluride (Bi 2 Te 3 ) substitute for cooling and waste heat conversion applications. However, the material is also known for its sensitivity on synthesis conditions as indicated by various reports on the same nominal composition which show greatly differing TE properties and performance. This indicates a fundamental lack of synthesis control and synthesiscomposition-property relationship knowledge. In this work, we establish a modified synthesis route with improved control over the effective sample stoichiometry which allows for reproducible high-performance properties ( zT max = 1.34 ± 0.19 at 561 K) and for systematically targeting different thermodynamic states of MgAgSb. This phase boundary mapping reveals that the homogeneity range for MgAgSb is very small (