Ostwald ripening behavior triggered by liquid Bi _0.4 Sb _1.6 Te ₃ for regulating thermoelectric transport in Cu ₂ Se alloy

Abstract Thermoelectric properties can be effectively improved by elaborately designing and controlling the internal structure during the sintering process. Enlightened by liquid phase sintering, a relatively stable system of Cu 2 Se– x wt% Bi 0.4 Sb 1.6 Te 3 (BST) with embedded novel core–shell precipitates were designed. Under the combined action of alternating thermal cycle regulation and longitudinal pressure, a gradual dynamic evolution and repeated redistribution of BST liquid existed above the eutectic temperature. The liquid BST phase grew in situ along grain boundaries and connected to form a network, potentially providing a “fast lane” for carrier transport, suppress the thermal conductivity while holding high carrier mobility. This eventually led to an elevated figure‐of‐merit ( zT ) of 0.64 at 700 K in Cu 2 Se–1 wt% BST, facilitated by presence of heterointerfaces and distorted lattice. The proposed cyclic hot‐pressed liquid phase sintering process, which is aimed at precipitate stabilization, provides a new paradigm for design and is applicable to other thermoelectric materials.