Effect of the sintering pressure on structure and microstructure of the filled skutterudite Sm_y(Fe_xNi_1-x)₄Sb₁₂ (x = 0.50–0.80, y = 0.17–0.55)

A structural and microstructural study was performed on several compositions of the Sm_y(Fe_xNi_1-x)₄Sb₁₂ system treated at three different pressures during the spark plasma sintering (SPS) process. Aim of the study is to recognize the effect of applied pressure at a fixed temperature on composition, microstrain and domains size, due to the relevance of these parameters in driving the thermoelectric properties of the material. Increasing pressure induces a change in the Sm amount, as well as an increase in microstrain and a decrease in the diffraction domains size. At the same time, enhancing pressure above a certain threshold promotes the formation of the extra phase (Sm,Fe,Ni)Sb₂, and hence a large power factor reduction. Relying on data collected in this work, applying a pressure close to 180 MPa during SPS results to be a good compromise between advantages in terms of microstructure and transport properties, and disadvantages in terms of phase purity.