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Polycrystalline K-filled CoSb3 are synthesized successfully. The uplimit for K filling is at least 0.45, being higher than those of either alkaline-earth (AE) or rare-earth (RE) metals but being in consistent with our earlier theoretical prediction. The measured transport properties (300–800K) show that K filling does not lower thermal conductivity much in comparison with AE or RE filling due to the relatively low mass of K atom. However, it improves electrical conductivity, retains large Seebeck coefficient, and leads to a reasonably good thermoelectric performance for the filled skutterudites. The maximum figure of merit ZT reaches 1 at 800K for K0.38Co4Sb12.

Composites containing Yb-filled CoSb3 and well-distributed Yb2O3 particles are synthesized by in situ reaction method. The structural, chemical, and transport properties of the composites are studied. Some Yb2O3 particles with microsize locate at the grain boundaries of matrix and others distribute within YbyCo4Sb12 grains as nanoscale inclusions. The combination of the “rattling” of Yb ions inside the voids of CoSb3 and the phonon scattering of the oxide defects results in a remarkable reduction in the lattice thermal conductivity. The thermoelectric performance of the composites is significantly improved, and the maximum figures of merit reach 1.3 for the Yb0.25Co4Sb12∕Yb2O3 and 1.2 for the Yb0.21Co4Sb12∕Yb2O3 composites at 850K.

Ferroelectric domain structure, especially the domain boundary polarization, in as-grown and poled (111)-cut PMN-30%PT single crystal has been studied by means of out-of-plane and in-plane piezoresponse force microscopies (PFMs). It revealed that the as-grown sample exhibits speckle-shaped microdomains, and the domain number distribution decreases exponentially as the domain size increases which can be described by the random field Ising model; in contrast, the poled sample shows stripe-shaped domains. Capacitive force-free PFM revealed a detailed domain boundary characteristic with net in-plane polarization. The presence of the in-plane polarization at the domain boundary also suggests the existence of orthorhombic phase in the rhombohedral matrix.