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

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 × 10$^{16}$ m$^{-2}$ in Bi$_{0.96}$ Pb$_{0.04}$CuSeO 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.