Improvement of Bi2Sr2Co2Oy thermoelectric performances by Na doping

Abstract

Bi2Sr2-xNaxCo2Oy thermoelectric materials with x = 0, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15 have been prepared by the classical solid state reaction. Microstructure has shown an important grain growth when Na is added, leading to very high bulk densities confirmed through density measurements. These modifications have produced a drastic decrease of electrical resistivity without significant modification of Seebeck coefficient. As a consequence, Power Factor has been increased in all Na-doped samples, reaching the maximum value (0.21 mW/K2.m at 650 °C) for 0.075 Na samples, which is fairly close to the reported for single crystals.