MmFe4Sb12- and CoSb3-based nano-skutterudites prepared by ball milling: Kinetics of formation and transport properties

A new generation of p-type didymium skutterudites with high ZT

“…Then the stoichiometric amounts of E y (Ca, Ba with a purity of 99.99 mass % from Alfa Aesar, Germany, DD of 99.9 mass % purity from Treibacher Industrie AG) was added, the samples were sealed under vacuum into quartz tubes, heated for 3 days at 550e600 C, melted at 950 C, air quenched and in some cases annealed for 2 days at 600 C. Electropositive elements and antimony were added in a weight excess of 3e5% in order to compensate evaporation losses during the preparation. The samples were then either ground in a tungsten carbide mortar into fine powders, filtered through a micro strainer to get particles below 20 mm (further on referred to as hand milled, HM) or were ground in a Fritsch Pulverisette high energy ball mill (further on referred to as ball milled, BM), which produces powders with a grain size below 100e200 nm [48,52,53]. In order to avoid oxidation all powder manipulations were performed in a Miller Howe glove box system (O 2 and H 2 O content below 3 ppm).…”

Multifilled nanocrystalline p-type didymium – Skutterudites with ZT>1.2

“…The samples were then sealed under vacuum into quartz tubes, heated for 4 days at 600 C, melted at 950 C and air quenched. The reguli were ground in a ball-mill (BM) to a grain size of 100e200 nm [20,21,30,31]. For single-filled alloys the milled powders were loaded in a 10 mm diameter graphite die inside a glove box and hot pressed under Ar employing a uniaxial hotpress system (HP W 200/250-2200-200-KS) at 600 C and 56 MPa during 2 h. In case of triple and multi-filled skutterudites the powders were mixed in the required weight proportion in the ball-mill and then hot pressed as described above.…”

“…Instrumental broadening of the diffraction maxima is accounted for by using an internal standard (Si), defining the instrument independent FWHM (b). For details of the crystallite size evaluation see [30].…”

“…In continuation of our recent investigations [20,21], DD was chosen because it is not only a "natural" double filler consisting of praseodymium and neodymium, but is cheaper than the respective pure rare earths and showed a good thermoelectric performance in skutterudites such as DD 0.65 Fe 3 CoSb 12 with a ZT ¼ 1.2 at 700 K. Based on a report of X. Tang et al [22], stating that for p-type skutterudites R y Fe x Co 4Àx Sb 12 (R ¼ Ce, Ba) the Seebeck coefficient increased with increasing R filling we tried to reach a filling level as high as possible. Nanostructured materials enhance phonon scattering and thus lower the thermal conductivity of thermoelectric materials [15,23e31], and in some cases improve the power factor [15,25,26,30]. There are various production routes of nanoparticles, but because of good results in our laboratory so far [21,30,31], we chose ball-milling.…”

“…Nanostructured materials enhance phonon scattering and thus lower the thermal conductivity of thermoelectric materials [15,23e31], and in some cases improve the power factor [15,25,26,30]. There are various production routes of nanoparticles, but because of good results in our laboratory so far [21,30,31], we chose ball-milling. The grain size and dislocation distribution were exemplarily investigated in Ca 0.20 Sr 0.12 DD 0.39 Fe 3 CoSb 12 .…”