Growth rate effect on microstructure and thermoelectric properties of melt grown Bi 2 Ba 2 Co 2 O x textured ceramics

Abstract

Bi₂Ba₂Co₂O_x thermoelectric (TE) ceramics have been grown from the melt using the laser floating zone method at different growth rates (15, 30 and 90 mm h⁻¹). Microstructural analysis has shown an improvement of the grain alignment and a reduction of secondary phases when the growth speed is decreased. These microstructural features have been reflected in the TE performances, with a reduction of the electrical resistivity and, as a consequence, at significant increase in the power factor values, reaching ∼0·15 mW K⁻² m⁻¹ at 650°C for the samples grown at 15 mm h⁻¹, which is much higher than the typical values obtained in these materials.