Influence of sintering temperature and Li + /Mg 2+ doping on the thermoelectric properties of Bi 2−2 x Li x Mg x Sr 2 Co 2 O y

Abstract

Bi_2−2xLi _x Mg _x Sr₂Co₂O _y (x = 0.05, 0.10 and 0.15) samples are prepared by a solid-state reaction at various temperatures (1033–1133 K). All X-ray diffraction peaks can be indexed as the monoclinic Bi₂Sr₂Co₂O _y phase. The structural and thermoelectric properties of Bi_2−2xLi _x Mg _x Sr₂Co₂O _y samples are systematically investigated, depending on the sintering temperature and the Li⁺/Mg²⁺ concentration. A higher sintering temperature increases the hole concentration and hole mobility, whereas a higher Li⁺/Mg²⁺ concentration increases the hole concentration and decreases the hole mobility. As the Li⁺/Mg²⁺ concentration increases, the power factor of the samples sintered at 1033 K decreases, whereas that of the samples sintered at 1083 and 1133 K increases. Of the prepared samples, Bi_1.70Li_0.15Mg_0.15Sr₂Co₂O _y sintered at 1133 K shows the largest power factor (0.25 × 10⁻⁴ W m⁻¹ K⁻²) at 973 K. This power factor is 2.5 times greater than that of Bi_1.70Li_0.15Mg_0.15Sr₂Co₂O _y sintered at 1033 K (0.10 × 10⁻⁴ W m⁻¹ K⁻²) at 973 K.