Double-doped skutterudite CoSb compounds are reported as a good n-type thermoelectric system which operate in the mid-temperature range. Instead of filling the skutterudite phase to minimize the thermal conductivity, it is proposed to induce disorder in the pnicogen rings by the substitution of Zn/Cd/Sn and Se. Structural analyses of the prepared compounds were carried out by Rietveld refinement process. The compounds show overall reduction in thermal conductivity, particularly the lattice part. Since vibration modes of heat-carrying phonons predominantly fall within the frequency range of the pnicogen rings, double substitutions on those pnicogen rings are particularly helpful in distracting the thermal transport. As larger mass difference and strain fluctuations can more efficiently scatter the heat-carrying phonons through short mean free path, it drastically restrains the thermal transport of the compounds, and this effect has been successfully demonstrated using the Debye-Callaway-Klemens model. Smooth electrical transport behavior is observed in all the samples and the power factor values are quite comparable to reported values. Phonon scattering mechanism and local distortion in the structure of the compounds is also evaluated by Raman analysis. Collectively, a high peak ZT of ∼0.7 and ∼0.65 at 673 K is obtained for CoSbSeZn and CoSbSeSn compounds which shows more than 50% enhancement relative to the pristine CoSb system.

Single crystalline titled phase is synthesized by conventional high-temperature solid-state synthesis. Crystal structure of Ni 3 GaSb is re-investigated by single-crystal X-ray diffraction and energy dispersive X-ray analysis. The compound crystallizes in P6 3 /mmc space group, the structure can be described as an intermediate of NiSb and Ni 2 In structures, similar to Ni 3 GaAs. Electronic structure of the compound is investigated by firstprinciples electronic structure calculations on the ordered model of Ni 3 GaSb. Stability and bond analysis was done by COHP calculations. Hetero-atomic NiÀ Sb and NiÀ Ga interactions play a major role towards to stability of the compound, these interactions are also responsible to modify the electronic structure of the titled compound. It was tested for catalytic activity and selectivity for acetylene hydrogenation reaction. Ni 3 GaSb was found to be a selective catalyst with 95.53 % C 2 H 2 conversion giving 60 % selectivity towards C 2 H 4 at 550°C.

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The pseudobinary Mn x Ni 2 Zn 11– x γ-brass-type phases at low Mn dopant levels ( x = 0.1–0.5) were investigated. Crystal structures were determined for the two loading compositions of x = 0.3 and 0.5. The structures were solved in the cubic space group of I 3 m and are described in close analogy to the Ni 2 Zn 11 parent γ-brass that is based on the 26-atom cluster, consisting of inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and cuboctahedron (CO). The refined site occupancies of the Mn x Ni 2 Zn 11– x ( x = 0.3, 0.5) reveal that the cluster center, which is empty in the Ni 2 Zn 11 , shows a partial occupation by Zn, with a partial depletion of Zn at the IT sites. The OH sites show a mixed Zn/Mn occupation. The OT and CO sites remain intact with respect to Ni 2 Zn 11 . Magnetic properties were studied for the Mn 0.3 Ni 2 Zn 10.7 composition. The temperature-dependent zero-field-cooled and field-cooled magnetization, the ac susceptibility, the M ( H ) hysteresis curves, the thermoremanent magnetization, and the memory effect demonstrate typical broken-ergodicity phenomena of a magnetically frustrated spin system below the spin freezing temperature T f ≈ 16 K. The Mn 0.3 Ni 2 Zn 10.7 γ-brass phase classifies as a spin glass, originating predominantly from the random distribution of diluted Mn moments on the octahedral partial structure.