Heterostructures that consist of a germanium antimony telluride matrix and cobalt germanide precipitates can be obtained by straightforward solid-state synthesis including simple annealing and quenching procedures. The microscale precipitates are homogeneously distributed in a matrix with pronounced "herringbone-like" nanostructure associated with very low thermal conductivities. In comparison to the corresponding pure tellurides, the figure of merit (ZT) values of heterostructured materials are remarkably higher. This is mostly due to an increase of the Seebeck coefficient with only little impact on the electrical conductivity. In addition, the phononic part of the thermal conductivity is significantly reduced in some of the materials. As a result, ZT values of ca. 1.9 at 450 °C are achieved. Temperature-dependent changes of the thermoelectric properties are well-understood and correlate with complex phase transitions of the telluride matrix. However, the high ZT values are retained in multiple measurement cycles.

The element distribution in the crystal structure of the stable phase of the well-known phase-change material Ge 2 Sb 2 Te 5 was determined at temperatures up to 471 uC using single crystals synthesized by chemical transport reactions. Because of the similar electron count of Sb and Te, the scattering contrast was enhanced by resonant diffraction using synchrotron radiation (beamline ID11, ESRF). A simultaneous refinement on data measured at the K-absorption edges of Sb and Te as well as at additional wavelengths off the absorption edges yielded reliable occupancy factors of each element on each position (a = 4.2257(2) Å, c = 17.2809(18) Å, P3m1, R 1 (overall) = 0.037). The dispersion correction terms Df 9 were refined and match experimental ones obtained from fluorescence spectra by the Kramers-Kronig transform. The structure contains distorted rocksalt-type blocks of nine alternating cation and anion layers, respectively, which are separated by van der Waals gaps between Te atom layers. Ge atoms prefer the cation positions near the center of the rocksalt-type block (occupancy factors Ge 0.60(4) Sb 0.36(2) ), Sb atoms the one near the van der Waals gap (Ge 0.33(7) Sb 0.66 (4) ). Anti-site disorder is not significant. During heating up to 471 uC and subsequent cooling, a reversible structural distortion was observed. The refinements show that with increasing temperature the first pair of anion and cation layers next to the van der Waals gap becomes slightly detached from the block and increasingly resembles a GeTe-type layer. Thus, the difference between interatomic distances in the 3 + 3 cation coordination sphere of the mixed Ge-Sb position next to the gap becomes more pronounced. The element distribution, in contrast, neither changes during the heating experiment nor upon long-time annealing. Thus, the behavior of 9P-Ge 2 Sb 2 Te 5 single crystals is predominantly under thermodynamic control.

Owing to a parity allowed 4f(6)((7)F)5d(1)→4f(7)((8)S(7/2)) transition, powders of the nominal composition Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) (2 mol% Eu(2+)) show surprising intense blue emission (λ(em)=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr(1-x)Ba(x)Si(2)O(2)N(2):Eu(2+), the described compound is a promising phosphor material for pc-LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X-ray diffraction methods was used to determine the crystal structure of Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+). HRTEM images reveal the intergrowth of nanodomains with SrSi(2)O(2)N(2) and BaSi(2)O(2)N(2)-type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi(2)O(2)N(2)-type domains was refined on single-crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON(3)-tetrahedra in pure BaSi(2)O(2)N(2), in Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.

SummaryThe causative agent of Legionnaires' disease, Legionella pneumophila, employs the autoinducer compound LAI-1 (3-hydroxypentadecane-4-one) for cell-cell communication. LAI-1 is produced and detected by the Lqs (Legionella quorum sensing) system, comprising the autoinducer synthase LqsA, the sensor kinases LqsS and LqsT, as well as the response regulator LqsR. Lqs-regulated processes include pathogen-host interactions, production of extracellular filaments and natural competence for DNA uptake. Here we show that synthetic LAI-1 promotes the motility of L. pneumophila by signalling through LqsS/LqsT and LqsR. Upon addition of LAI-1, autophosphorylation of LqsS/LqsT by [γ-

The structure elucidation of the novel sulfide telluride Pb8Sb8S15Te5 demonstrates a new versatile procedure that exploits the synergism of electron microscopy and synchrotron diffraction methods for accurate structure analyses of side-phases in heterogeneous microcrystalline samples. Suitable crystallites of unknown compounds can be identified by transmission electron microscopy and relocated and centered in a microfocused synchrotron beam by means of X-ray fluorescence scans. The refined structure model is then confirmed by simulating HRTEM images of the same crystallite. Pb8Sb8S15Te5 consists of chains of heterocubane-like units. Cation coordination polyhedra form unusually entwined chains of edge- and face-sharing bicapped trigonal prisms. The structure data are precise enough for bond-valence calculations, which confirm the disordered atom distribution. On this basis, optimization of physical properties becomes feasible.