Spinodal decomposition in (CaxBa1−x)yFe4Sb12

Abstract

The thermoelectric and structural properties of a double filled skutterudite solid solution (CaxBa1−x)yFe4Sb12 were investigated. Using X-ray powder and X-ray micro analyses (EPMA) an immiscibility gap was established with a critical point at x≈0.45 and a critical temperature that depends on the filling level (TC=590±5°C at y=0.8 and TC=610±5°C at y=0.9). The thermoelectric properties were measured for samples prepared in four different states: (i) a single phase solid solution (CaxBa1−x)yFe4Sb12; (ii) a two phase microcrystalline mixture of CayFe4Sb12 and BayFe4Sb12; (iii) a single phase structure obtained after annealing of the latter sample at 600°C for 200h; (iv) a spinodally demixed sample after annealing at 400°C for 672h. The thermoelectric properties of the phase mixture (ii) are compatible with data reported for the microcrystalline end members (CayFe4Sb12 and BayFe4Sb12), whilst the single phase (i and iii) and spinodally decomposed (iv) samples show increased thermopower and decreased thermal conductivity, similarly to those observed for nano-structured CayFe4Sb12 and BayFe4Sb12.