No abstract

Engineering lattice thermal conductivity requires to control the heat carried by atomic vibration waves, the phonons. The key parameter for quantifying it is the phonon lifetime, limiting the travelling distance, whose determination is however at the limits of instrumental capabilities. Here, we show the achievement of a direct quantitative measurement of phonon lifetimes in a single crystal of the clathrate Ba7.81Ge40.67Au5.33, renowned for its puzzling ‘glass-like’ thermal conductivity. Surprisingly, thermal transport is dominated by acoustic phonons with long lifetimes, travelling over distances of 10 to 100 nm as their wave-vector goes from 0.3 to 0.1 Å−1. Considering only low-energy acoustic phonons, and their observed lifetime, leads to a calculated thermal conductivity very close to the experimental one. Our results challenge the current picture of thermal transport in clathrates, underlining the inability of state-of-the-art simulations to reproduce the experimental data, thus representing a crucial experimental input for theoretical developments.

Supporting information available online at http://www.thieme-connect.de/products ABSTR AC TGinsenoside Rh1 is one of major bioactive compounds extracted from red ginseng, which has been increasingly used for enhancing cognition and physical health worldwide. The objective of this study was to review the pharmacological effects of ginsenoside Rh1 in a systematic manner. We performed searches on eight electronic databases including MEDLINE (Pubmed), Scopus, Google Scholar, POPLINE, Global Health Library, Virtual Health Library, the System for Information on Grey Literature in Europe, and the New York Academy of Medicine Grey Literature Report to select the original research publications reporting the biological and pharmacological effects of ginsenoside Rh1 from in vitro and in vivo studies regardless of publication language and study design. Upon applying the inclusion and exclusion criteria, we included a total of 57 studies for our systemic review. Ginsenoside Rh1 exhibited the potent characteristics of anti-inflammatory, antioxidant, immunomodulatory effects, and positive effects on the nervous system. The cytotoxic effects of ginsenoside Rh1 were dependent on different types of cell lines. Other pharmacological effects including estrogenic, enzymatic, anti-microorganism activities, and cardiovascular effects have been mentioned, but the results were considerably diverged. A higher quality of evidence on clinical trial studies is highly recommended to confirm the consistent efficacy of ginsenoside Rh1.

The clathrate-I phase Ba8AlxSi46-x has been structurally characterized at the composition x = 6.9 (space group Pm3[combining macron]n, no. 223, a = 10.4645(2) Å). A crystal structure model comprising the distribution of aluminium and silicon atoms in the clathrate framework was established: 5.7 Al atoms and 0.3 Si atoms occupy the crystallographic site 6c, while 1.2 Al atoms and 22.8 Si atoms occupy site 24k. The atomic distribution was established based on a combination of (27)Al and (29)Si NMR experiments, X-ray single-crystal diffraction and wavelength-dispersive X-ray spectroscopy.

The new clathrate-I phase Ba(8)Rh(x)Si(46-x-y□y) (2.36 < x < 2.74; y = 0.65 for x = 2.74), Pearson symbol cP54, space group Pm3[combining macron]n, was prepared as a single phase and characterized. For these compositions, the lattice parameter does not change significantly and was found to be a = 10.347(1) Å. Phase relations were investigated by means of metallographic and thermal analyses. The incongruently melting phase Ba(8)Rh(x)Si(46-x-y□y) was obtained by annealing a solidified melt of the stoichiometric composition at 1000 °C for five days. Below 850 °C, the clathrate phase slowly decomposes to BaSi(2), Si and the new compound BaRh(2)Si(9). Crystal structure and vacancy concentration were investigated by means of single crystal and powder X-ray diffraction and wavelength dispersive X-ray spectroscopy analyses. Quantum chemical calculations show that the Rh 4d states hybridize with Si 3p states so that the DOS structure cannot be simply deduced in a rigid band approach from that of the binary Ba(8)Si(46). Analysis of the chemical bonding applying the ELI-D approach yielded covalent two-center two-electron bonds between Rh and Si atoms. For the composition Ba(8)Rh(2.74)Si(42.61□0.65), a temperature dependent diamagnetic susceptibility and an almost temperature independent electrical resistivity (ρ≈ 5 μΩm) were observed. The magnitude of the negative Seebeck coefficient is increasing linearly with temperature from 0 μV K(-1) at 2 K to -35 μV K(-1) at 850 K indicating n-type electrical conductivity.