Microstructures and thermoelectric properties of spin-cast Co0.97Cr0.03Sb3 ribbons

The ribbons of Co_0.97Cr_0.03Sb₃ were fabricated by spin-casting on a rotating copper roll with the surface-velocity of 3-50 m/s and were annealed for 10.8 ks at 873 K. The microstructures were investigated by means of X-ray diffraction measurements, scanning and transmission electron microscopic observations. The thermoelectromotive force and electrical conductivity were measured under a vacuum. As the surface-velocity increases, the amount of CoSb₃ in the as-cast ribbon decreases, because the peritectic reaction of CoSb₂+L→CoSb₃ is suppressed due to rapid cooling. After annealing, the amount of CoSb₃ increases with increasing the surface-velocity, because the reaction of CoSb₂+Sb→CoSb₃ proceeds more sufficiently during annealing. The morphology of crystal grains and lattice defects depend on the surface-velocity. As the surface-velocity increases, the thermoelectromotive force of the as-cast ribbon decreases, but the one of the annealed ribbon increases prior to decreasing. The maximum thermoelectromotive force and electrical conductivity, resulting in the maximum power factor, are attained at the surface velocity of 10 m/s