Thermoelectric properties of BiBO<sub>3</sub>-added Bi<sub>2</sub>Sr<sub>2</sub>Co<sub>2</sub>O<i><sub>y</sub></i> ceramics

The thermoelectric properties of BiBO3-added Bi2Sr2Co2Oy ceramics have been investigated. Bi2Sr2Co2Oy + x wt % BiBO3 materials (x = 0, 0.16, 0.50, and 0.80) were prepared by the sol–gel method. The values of power factor (PF) and figure of merit (ZT) were evaluated using electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (k) measurements. The Bi2Sr2Co2Oy + 0.16 wt % BiBO3 sample has the lowest ρ among all studied materials. The S rises with a rising temperature above 400 K, indicating p-type conductivity for each sample. The value of S for the reference (pristine) Bi2Sr2Co2Oy at 973 K is approximately 3–10 % higher than the BiBO3-added compositions. Reference and 0.16 wt % BiBO3-added samples exhibit higher PF values than those with higher BiBO3 content (x = 0.50 and 0.80). Adding bismuth borate (x > 0.16) leads to a 1.6-fold decrease in the thermal conductivity of the Bi2Sr2Co2Oy system at 573 K. The decrease of ρ (x = 0.16) and k (for all BiBO3-added compositions) resulted in a 39 % improvement in the ZT value.