Effect of additives on the formation of bismuth nanoparticles by polyol process

Formation of bismuth nano-particles by polyol process have been studied in terms of the effect of additives on its size and shape. Bismuth trichloride solved in ethylene glycol was reduced at high temperature with the existence of poly(vinylpyrrolidone) (PVP) and ferric chloride. Spherical particles were mostly formed with the solitary addition of PVP. Sphere size was decreased from 400 to 200nm with increasing amount of the PVP. Addition of larger weight-average molecular weight (M_w) of the PVP decreased the sphere size slightly. On the other hand, hexagonal or rectangular plate-like particles were obtained at a high number ratio over 70% by the co-addition of ferric chloride with the PVP. Plate size and the fraction of plate-like particles tended to increase slightly with the increase of amount of the PVP. The plate size also increased with increase of molecular weight of the PVP and square plate-like particles larger than 1 micrometer were obtained with the addition of the large molecular size of PVP (M_w ∼1,300,000). Adequate amount and size of PVP tended to decrease totally the growth speed of particles and to suppress coalescence with each other, and ferric ions suppressed the growth speed toward the c-axis by alternative re-oxidization of bismuth metal.