Amorphous framework doping of Bi_0.4Sb_1.6Te₃ thermoelectrics via Prussian Blue-derived phases

Bi_0.4Sb_1.6Te₃ (BST) is a benchmark thermoelectric material near room temperature, but further improvement in zT requires stronger suppression of lattice thermal conductivity without severely degrading electronic transport. Here, Prussian blue (PB), a cyanide-bridged coordination framework, is introduced as a structurally tunable second phase. Thermal pretreatment transforms crystalline PB into an amorphous PB-derived framework that loses long-range periodicity while retaining short-range Fe–C–N coordination, mixed Fe valence states, and mesoporosity. Compared with crystalline PB, the amorphous PB-derived phase more effectively suppresses lattice thermal conductivity through enhanced structural disorder, heterogeneous interfaces, and pore-related phonon scattering, while causing only a moderate deterioration of electronic transport. The enhanced Seebeck coefficient partly compensates for the reduced electrical conductivity, whereas the dominant contribution to the zT enhancement originates from the pronounced reduction in lattice thermal conductivity rather than from an increase in power factor. Consequently, the optimized BST/0.8 wt% 573 K PB composite achieves a peak zT of approximately 1.56 over 325–375 K, an average zT of approximately 1.27 over 300–500 K, and a measured prototype-module conversion efficiency of about 7.0% at ΔT = 231 K. These results demonstrate that amorphous PB-derived framework domains provide effective broadband phonon scattering with limited degradation of electronic transport in Bi–Sb–Te thermoelectrics.