Ultrahigh‐Pressure Structural Modification in BiCuSeO Ceramics: Dense Dislocations and Exceptional Thermoelectric Performance

Abstract Dislocations as line defects in crystalline solids play a crucial role in controlling the mechanical and functional properties of materials. Yet, for functional ceramic oxides, it is very difficult to introduce dense dislocations because of the strong chemical bonds. In this work, the introduction of high‐density dislocations is demonstrated by ultrahigh‐pressure sintering into a typical ceramic oxide, BiCuSeO, for thermoelectric applications. The ultrahigh‐pressure induces shear stresses that surpass the critical strength for dislocation nucleation, followed by dislocation glide and profuse multiplication, leading to a high dislocation density of ≈9.1 × 10¹⁶ m⁻² in Bi_0.96Pb_0.04CuSeO ceramic. These dislocations greatly suppress the phonon transport to reduce the lattice thermal conductivity, reaching 0.13 Wm⁻¹ K⁻¹ at 767 K and resulting in a record‐high zT of 1.69 in this oxide thermoelectric ceramic. This study demonstrates the feasibility of generating dense dislocations in ceramic oxides via ultrahigh‐pressure sintering for tuning functional properties.