Bi2Te3 filaments via extrusion and pressureless sintering of Bi2Te3-based inks

Inks containing sub-20 µm particles of doped bismuth telluride (n-type Bi2Te2.73Se0.3 or p-type (Bi0.5Sb1.5)Te3) are extruded into 330 µm diameter filaments. When solid-state sintered up to 857 K under no pressure, the filaments only partially densify, with over 20% porosity remaining. Coating the filament with TeO2 powder, followed by hydrogen reduction to liquid Te, enables liquid phase sintering at 710 K, with rapid densification to less than 5% porosity within 1 h. Coating with a stoichiometric blend of Bi2O3 + 3TeO2 powders, followed by hydrogen reduction to liquid Bi and Te, provides transient liquid phase sintering at 808 K and subsequent reaction to Bi2Te3, resulting in fast filament densification, to less than 5% porosity within 10 min without residual Te.