Effects of high entropy combined with Cu/Ag doping on the thermoelectric properties of Bi2Sr2Co2Oy ceramics

A series of Bi2Sr2Co2Oy (BSCO), Bi2(Sr2/3Ba2/3Ca2/3)Co2Oy (BSBCCO), Bi1.9Cu0.1(Sr2/3Ba2/3Ca2/3)Co2O (BCSBCCO) and Bi1.8Ag0.2(Sr2/3Ba2/3Ca2/3)Co2Oy (BASBCCO) ceramic samples were prepared to optimize the thermoelectric properties of BSCO by high entropy doping combined with Cu/Ag doping. High entropy doping improves the carrier mobility significantly, due to a sintering effect in liquid phase and an additional conduction path. Cu/Ag acceptor doping increases the carrier concentration and Seebeck coefficients. Both them enhance the electrical transport performance of doped samples effectively. Specially, the random distribution of several different cations caused by high entropy doping and Cu/Ag doping can enhance the phonon scattering, which greatly reduces the thermal conductivity of doped samples. Finally, the thermoelectric figure of merit (ZT) value of the BASBCCO sample is improved to 0.36 at 923 K on the basis of high entropy doped BSBCCO (ZT = 0.28 923 K), which is twice that of the pristine sample.