Microstructures and thermoelectric properties of (FeSb3) 1-xLax ribbons

The microstructures and thermoelectric properties of the spin-cast (FeSb₃)_1-xLa_x (x=0-0.4) ribbons were investigated by means of X-ray diffraction measurements, transmission electron microscopic observations, EDX analyses, measurements of the electrical resistivity and thermoelectromotive force. The ribbons consist of various structures : FeSb₂+Sb for x=0, LaFe₄ Sb₁₂+FeSb₂+Sb for x=0.1, LaFe₄Sb ₁₂ for x=0.2, LaFe₄Sb₁₂+La₂Sb+LaSb+LaSb₂ +FeSb for x=0.3 and 0.4, where LaFe₄Sb₁₂ is the filled skutterudite structure. A precipitation zone appeared along the grain boundaries of LaFe₄Sb₁₂ for x>0.2, while it was not seen for x<0.2. As the amount of LaFe₄Sb ₁₂ decreases with deviation from x=0.2, the electrical resistivity decreases more rapidly for x>0.2 than for x<0.2. The Seebeck coefficient is large between x=0.2 and 0.3. The large power factor is obtained between x=0.2 and 0.3, being the high value of 20 μW/cmK² at 350 K and 50 μW/cmK² at 550 K