Low thermal conductivity and enhanced thermoelectric properties of Cu-substituted Bi2-xCuxSr2Co2Oy ceramics

The Bi2Sr2Co2Oy ceramic, known for its stability as a p-type thermoelectric material, has limited thermoelectric performance that necessitates enhancement. In this study, Bi2-xCuxSr2Co2Oy (x = 0, 0.025, 0.05, 0.1, 0.2) ceramic samples were synthesized using the conventional solid-state reaction method. Substitution of Cu2+ for Bi3+ in the samples increased carrier concentration, significantly reducing electrical resistivity. Utilizing the single parabolic band (SPB) model, it was determined that Cu incorporation led to an increased effective mass, thereby enhancing the Seebeck coefficient. Additionally, fine grains and lattice defects induced by Cu2+ substitution effectively scattered phonons, resulting in an ultra-low thermal conductivity of 0.59 Wm(-1)K(-1) at 923 K for the Bi1.8Cu0.2Sr2Co2Oy sample. Consequently, Cu substitution optimized both the electrical and thermal transport properties of Bi2-xCuxSr2Co2Oy samples. The dimensionless thermoelectric figure of merit (ZT) for Bi1.95Cu0.05Sr2Co2Oy reached 0.31 at 923 K, representing a 63 % increase over the pristine Bi2Sr2Co2Oy sample.