We propose a mixed-space approach using the accurate force constants calculated by the direct approach in real space and the dipole-dipole interactions calculated by linear response theory in reciprocal space, making the accurate prediction of phonon frequencies for polar materials possible using the direct approach as well as linear response theory. As examples, by using the present approach, we predict the first-principles phonon properties of the polar materials α-Al(2)O(3), MgO, c-SiC, and h-BN, which are in excellent agreement with available experimental data.

Low temperature transport properties of polycrystalline dual-element-filled skutterudites BaxRyCo4Sb12 (R=La, Ce, and Sr) are reported. Remarkably the combination of Ba and La or Ba and Ce is much more effective in reducing lattice thermal conductivity (κL) than Ba and Sr. The density-functional theory calculations and experimental data suggest that multiple-filled skutterudites using filler elements of different chemical natures, such as the rare earths, the alkaline earths, or the alkalines provide a broader range of resonant phonon scattering. The thermoelectric figure of merit of filled skutterudites can likely be improved by means of such multiple-element void filling.

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Controlled photoluminescence tuning is important for the optimization and modification of phosphor materials. Herein we report an isostructural solid solution of (CaMg)x(NaSc)1-xSi2O6 (0 < x < 1) in which cation nanosegregation leads to the presence of two dilute Eu(2+) centers. The distinct nanodomains of isostructural (CaMg)Si2O6 and (NaSc)Si2O6 contain a proportional number of Eu(2+) ions with unique, independent spectroscopic signatures. Density functional theory calculations provided a theoretical understanding of the nanosegregation and indicated that the homogeneous solid solution is energetically unstable. It is shown that nanosegregation allows predictive control of color rendering and therefore provides a new method of phosphor development.

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.

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