Ink Casting and 3D-Extrusion Printing of Yb14MnSb11 for High-Temperature Thermoelectric Material

Abstract

Complex shapes are created from Yb₁₄MnSb₁₁, a high-temperature thermoelectric Zintl phase, via a two-step process: i) layer-by-layer 3D-extrusion of ink containing partially-reacted powders which are ball-milled from a blend of Yb, MnSb, and Sb powders; ii) heat treatment to synthesize the ternary compound Yb₁₄MnSb₁₁ and densify the extruded powders. A high phase purity for Yb₁₄MnSb₁₁ (83–94%) is achieved in both cast and 3D-extruded ink specimens via a solid-state reaction between Yb, MnSb, and Yb₄Sb₃ during reactive sintering. Pressure-free sintering at temperatures of 1200–1400 °C densifies the powders to 82% relative density but can also induce the decomposition of the Yb₁₄MnSb₁₁ phase due to Yb sublimation. A process window with optimized sintering temperature and time is identified, achieving both low porosity and high phase purity and reaching a maximum zT = 0.61 at 1000 °C, about half of the maximum zT value for bulk Yb₁₄MnSb₁₁ made via conventional processes (pressure sintering of precursor powders). The present approach – direct ink writing of ball-milled powders, combined with reactive sintering – is a scalable and affordable method to fabricate thermoelectric legs with intricate 3D shapes, for enhanced performances in high-temperature thermoelectric applications.