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Research has been conducted on the antimony-doped Ba (sub)8 Ga (sub)16 Ge (sub)30 clathrates. Results indicate that these compounds grown as crystals from gallium flux form in the cubic space group and that more antimony than gallium incorporates into the material.

Comparisons of in situ simulated and experimental 2H NMR spectra were done to quantify the degrees of orientational order in the alkaline lyotropic silicate-surfactant liquid crystals. Results suggested that the macroscopic alignment of liquid crystallines are controlled through the adjustment of their composition which is evident in the adoption of different orientations by lamellar or hexagonal domains. Findings also reveal the importance of using liquid crystal processing strategies for organizing inorganic-organic hybrid materials over macroscopic and mesoscopic length scales.

The Czochralski method was used to grow a 46-mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance. The Seebeck coefficient and electrical and thermal conductivities all showed evidence of a transition from extrinsic to intrinsic behavior in the range of 600–900 K. The corresponding figure of merit (ZT) was found to be a record high of 1.35 at 900 K and with an extrapolated maximum of 1.63 at 1100 K. This makes the Ba8Ga16Ge30 clathrate an exceptionally strong candidate for medium and high-temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]

We examine the effects of monoderivatization on the electronic properties of C[sub 60]. For this we chose the phenyl-C[sub 61]-octanoic acid cholesteryl ester, [6,6]PCOCr, whose nonlinear optical properties have been investigated in the past. While the optical absorption spectrum of this methano fullerene is similar to that of C[sub 60], substantial differences are observed upon doping with potassium. Similarly, the doping-dependent conductivity of the functionalized fullerene shows two maxima as opposed to the single maximum for C[sub 60]. The experimental observations are consistent with the doping-induced degeneracy removal of the parent C[sub 60] LUMO (t[sub 1u]) orbital, which in potassium-doped methanofullerene splits into two components separated by about 0.5 eV. We provide experimental evidence that the doping of [6,6]PCOCr proceeds, as in C[sub 60], with six consecutive reduction (electron transfer) steps, yielding K[sub 6][ 6,6]PCOCr stoichiometry at the end. The transport in partially doped [6,6]PCOCr thin films occurs by thermally activated hopping of the charge carriers with activation energy E[sub a] ≅ 0.25 eV and hopping probability proportional to the number of unpaired electrons in the reduced molecule. [ABSTRACT FROM AUTHOR]

Multitemperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba[sub 8]Ga[sub 16]Si[sub 30] are reported. For the framework atoms reciprocal space structural refinements give total occupancies in the unit cell of Ga/Si=3.8/2.2, 1.8/14.2, 10.2/13.8 for the 6c, 16i, and 24k sites respectively, thus showing that Ga avoids the tetrahedral 16i positions. The guest atom displacement parameters obtained from structure factor fitting are analyzed with semianharmonic Einstein models giving Einstein temperatures (Θ[sub E]) of 69(1), 98(7), and 124(2) K for Ba(2)[sub (100)], Ba(2)[sub [100]], and Ba(1), respectively. The analysis furthermore suggests that all guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures. The structure factors are subsequently used in the maximum entropy method calculations to obtain direct space nuclear densities. These are modeled with anharmonic one-particle potential models to fourth order. Even at elevated temperatures anharmonicity is limited indicating that the low thermal conductivity of the clathrate has a different origin. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]