Effect of Mn-Sb Additive on Sinterability of Yb0.3Co4Sb12 Skutterudite Thermoelectric Materials

Yb0.3Co4Sb12 skutterudite, which is known for its ability to directly convert heat into electricity as a thermoelectric material, is typically manufactured in bulk via pressure sintering. In order to improve productivity, enhancing sinterability to reduce the applied pressure is crucial. Therefore, one approach for improving sinterability involves testing the application of a sintering aid. In pressureless sintering experiments performed under vacuum, Yb0.3Co4Sb12 skutterudite showed minimal sintering progress, even at temperatures approaching its decomposition point. Introducing of Mn fine powder as a sintering aid alongside Yb0.3Co4Sb12 under no pressure resulted in the formation of a neck structure, with the surrounding area showing evidence of an Mn–Sb phase solid solution near the mixed Mn powder. A liquid phase forms near the eutectic point owing to eutectic reactions between Mn and Sb, facilitating element diffusion and sintering. Therefore, Mn1.1Sb, a compound near the eutectic point, was chosen as a sintering aid. In hot-pressing experiments at various pressures, the density of the Yb0.3Co4Sb12 sintered bodies decreased at pressures of 35 MPa or less when Mn1.1Sb was not mixed in. However, the sintered bodies containing Mn1.1Sb maintained a high density even at low pressure (10 MPa). Comparing the sintered bodies hot pressed at 15 MPa, the sample without Mn1.1Sb exhibited increased electrical resistivity and decreased thermal conductivity, whereas the sample mixed with Mn1.1Sb showed electrical resistivity and thermal conductivity equivalent to those of the sintered body at 68 MPa. The dimensionless figure of merit ZT, representing thermoelectric performance, was also high at ZT = 1.23 at 500°C.