Growing Cobalt Triantimonide Using Vertical Bridgman Method and Effects of Post Annealing

Abstract

Crystals of CoSb3 were grown using the vertical Bridgman method at growth rates that varied from 0.4 to 2.8 mm/h. Thermoelectric properties were analyzed for both as-grown and post-annealed samples. Polycrystalline CoSb3 surrounded by Sb was obtained. Samples grown at the rate of 0.4 mm/h had larger CoSb3 grains than samples grown at the 2.8 mm/h rate. For the as-grown samples, the Seebeck coefficient was smaller than 200 μ/K, which is a nominal value [1–3]. The presence of residual Sb resulted in a decrease in the Seebeck coefficient and an increase in the samples' electrical conductivity. A subsequent heat treatment at 800 °C for 20 h eliminated the residual Sb, resulting in a significant increase in the Seebeck coefficients (ranging from > 200 μV/K) in the annealed samples, as compared with the as-grown samples. The samples with a higher growth rate had larger Seebeck coefficients of ∼500 μ/K after annealing.

Thermoelectric properties of undoped p-type CoSb3 prepared by vertical Bridgman crystal growth and spark plasma sintering

“…The samples annealed for more than 5 h demonstrate that the observed Seebeck coefficient has a high value in the relatively lower temperature range from 370 to 600 K, although CoSb 3 sintered in a conventional manner exhibits a maximum Seebeck coefficient at 600-750 K [7][8][9][10][11][12][13][14]. Compared with the expected Seebeck coefficient of ∼190 V/K for the present carrier concentration [15], the observed values are higher in the lower temperature region.…”

“…We have fabricated bulk CoSb 3 using the conventional vertical Bridgman method [11][12][13]. While single crystallike material was obtained with a growth rate of 0.4 mm/h, at a faster rate of 2.8 mm/h grains of CoSb 3 crystals surrounded by residual metallic Sb were grown [11].…”