Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe2O4 MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.

Barium and indium double-filled skutterudites ${\mathrm{Ba}}_x{\mathrm{In}}_y{\mathrm{Co}}_4{\mathrm{Sb}}_{12-z}$ have been synthesized by a melting method using a series of starting materials with nominal compositions ${\mathrm{Ba}}_{0.3-m}{\mathrm{In}}_m{\mathrm{Co}}_4{\mathrm{Sb}}_{12}$ $(0⩽m⩽0.3)$ . Rietveld structure refinement shows that both barium and indium occupied the Sb-icosahedron voids in skutterudite structure. The thermal vibration parameter $U_{\mathrm{iso}}$ of indium is an order of magnitude bigger than that of barium. The electron probe microanalysis data prove that the filling fraction limit of indium is about 0.22. Hall effect was measured by the Van de Pauw method at room temperature. All ${\mathrm{Ba}}_x{\mathrm{In}}_y{\mathrm{Co}}_4{\mathrm{Sb}}_{12-z}$ compounds exhibit $n$ -type conduction. The temperature dependences of electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured on these compounds in the range of $300–850\mathrm{K}$ . ${\mathrm{Ba}}_{0.13}{\mathrm{In}}_{0.14}{\mathrm{Co}}_4{\mathrm{Sb}}_{11.75}$ with close filling fractions for barium and indium exhibits anomalously excellent thermoelectric properties, which may be due to the presence of the localized state in the gap occupied by one electron from indium impurity. The lattice thermal conductivity of ${\mathrm{Ba}}_x{\mathrm{In}}_y{\mathrm{Co}}_4{\mathrm{Sb}}_{12-z}$ is significantly low compared to single barium-filled skutterudite ${\mathrm{Ba}}_{0.27}{\mathrm{Co}}_4{\mathrm{Sb}}_{11.85}$ and reached a minimum for ${\mathrm{Ba}}_{0.13}{\mathrm{In}}_{0.14}{\mathrm{Co}}_4{\mathrm{Sb}}_{11.75}$ . The dimensionless thermoelectric figure of merit $ZT$ increased with increasing temperature in the range of $300–675\mathrm{K}$ and reached a maximum value of 1.19 for ${\mathrm{Ba}}_{0.13}{\mathrm{In}}_{0.14}{\mathrm{Co}}_4{\mathrm{Sb}}_{11.75}$ at $850\mathrm{K}$ .

The nanostructures induced by uniaxial compression in ${\mathrm{Ce}}_{0.29}{\mathrm{Fe}}_{1.40}{\mathrm{Co}}_{2.60}{\mathrm{Sb}}_{11.24}$ bulk thermoelectric material is reported. High-resolution transmission electron microscope images reveal that the nanostructures consist of ${\mathrm{Ce}}_{0.31}{\mathrm{Fe}}_{1.38}{\mathrm{Co}}_{2.62}{\mathrm{Sb}}_{11.56}$ crystals and ${\mathrm{Fe}}_{0.34}{\mathrm{Co}}_{0.66}{\mathrm{Sb}}_{1.99}$ minicrystal/noncrystal with grain sizes about $5–20\mathrm{nm}$ . It is shown that the Seebeck coefficient is increased by 21%, the phonon thermal conductivity is reduced by 19%, while the electrical conductivity rises slightly at $300\mathrm{K}$ . This leads to a surprising increase in the power factor by 51%. The significant increase of Seebeck coefficient and the remarkable reduction of phonon thermal conductivity are believed to be due to quantum effect and size effect of the nanostructures, respectively.