EFFECT OF MAGNETIC-FIELD ON MACROSEGREGAT ION IN (BI,SB)(2)TE-3

A thermoelectric material (Bi0.25Sb0.75)(2)Te-3 was grown by a vertica l gradient freezing technique in high magnetic fields of up to 8 T. Th e radial distribution of composition showed macrosegregation when the specimens were solidified in the magnetic field. The radial segregatio n increased with increasing intensity of the magnetic field. On the ot her hand, the longitudinal distribution for both the specimens under 0 T and 8 T had a variation at the initial transient, but no effect of the magnetic field on the composition distribution was observed. A num erical calculation of the solid/liquid interface shape, thermal and so lutal fields suggested that the difference in thermal conductivity bet ween the solid and the liquid phases mould cause the concave interface shape and a driving force of the convection around the s/l interface. It was concluded that the interaction of the convection mass transfer reduced by the magnetic field interacts with the diffusion mass trans fer, causing the radial macrosegregation.