Synthesis and thermoelectric properties of double-atom-filled skutterudite compounds CamCenFexCo4−xSb12

Abstract

Single-phase CamCenFexCo4−xSb12 compounds filled by Ca and Ce were synthesized by using melting-quench-diffusion annealing reaction method. The structure and thermoelectric properties of double atoms filled skutterudite compounds were investigated. The results of Rietveld refinement indicate high reliabilities of filling fractions consistent with the inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis, CamCenFexCo4−xSb12 compounds possess skutterudite structure, and Sb-icosahedron voids were filled with Ca or Ce. The thermal parameter BCa∕Ce (6.0) of Ca∕Ce is much larger than that of BSb (0.3) and BFe∕Co (0.3) of Sb and Fe∕Co. The specific chemical states of atoms were obtained from x-ray photoelectron spectroscopy quantitative analysis, which shows that Sb has five chemical states and the relative content is correlative with the total filling fraction; the filling atoms have three filling positions and tend to fill the center position of the Sb-icosahedron voids, preferentially. With the same filling fraction, carrier concentration and electrical conductivity of p-type CamCenFexCo4−xSb12 are intervenient between that of single atom filled compounds CamFexCo4−xSb12 and CenFexCo4−xSb12, and decreased with increasing Ca and Ce, especially Ce, filling fraction. The Seebeck coefficients are increased with increasing total filling fraction, and the influence of Ce filling fraction to the Seebeck coefficients is more notable than that of Ca, and with the same filling fraction, the lattice thermal conductivity of CamCenFexCo4−xSb12 is smaller than that of CamFexCo4−xSb12 and CenFexCo4−xSb12; furthermore, when the total filling fraction (m+n) is about 0.3 and the respective filling fraction of Ca and Ce is approximately identical, the lattice thermal conductivity reached the minimum value. The greatest ZT value of 1.2 was obtained at 750K for p-type Ca0.18Ce0.12Fe1.45Co2.55Sb12 compound.