83 research outputs found
Clusters of the Heavier Elements of Main Groups 14â16: A Novel Synthetic Route for Polyanions in Molten Crown Ether
A novel procedure allows the synthesis of homoatomic polyanions directly from the elements E (E = Sn, As, Sb, Te) in molten A/18-crown-6 as reaction medium (A = K, Rb) at temperatures between 40 and 80° [1]. The reactions are carried out by adding E to mixtures of A and 18-crown-6 that proved to form stable melts under these conditions. Further work off using ethylenediamine or DMF as solvent yielded single crystals of the following compounds: [K(18-crown-6)]4Sn9 (1), [K(18-crown-6)]3KSn9·en (2), [K(18-crown-6)]3As7 (3), [K([2.2.2]crypt)]2[K(18-crown-6)]Sb7·0.5en (4), [Rb(18-crown-6)]3Sb7 (5), [K(18-crown-6)]2Te4 (6), and [K(18-crown-6)]2Te4·en (7). In all compounds short contacts between the Zintl ions and A-atoms are observed. The influence of cation-anion interactions on the structure of these anions is discussed
TbNb6Sn6: the first ternary compound from the rare earthâniobiumâtin system
The title compound, terbium hexaÂniobium hexastannide, TbNb6Sn6, is the first ternary compound from the rare earthâniobiumâtin system. It has the HfFe6Ge6 structure type, which can be analysed as an interÂgrowth of the Zr4Al3 and CaCu5 structures. All the atoms lie on special positions; their coordination geometries and site symmetries are: Tb (dodecaÂhedron) 6/mmm; Nb (distorted icosaÂhedron) 2mm; Sn (FrankâCaspar polyhedron, CN = 14â15) 6mm and
m2; Sn (distorted icosaÂhedron)
m2. The structure contains a graphite-type Sn network, Kagome nets of Nb atoms, and Tb atoms alternating with Sn2 dumbbells in the channels
Li5SnP3: a member of the series Li10+4xSn2âxP6 for x=0 comprising the fast lithiumâion conductors Li8SnP4 (x=0.5) and Li14SnP6 (x=1)
The targeted search for suitable solidâstate ionic conductors requires a certain understanding of the conduction mechanism and the correlation of the structures and the resulting properties of the material. Thus, the investigation of various ionic conductors with respect to their structural composition is crucial for the design of nextâgeneration materials as demanded. We report here on Li(5)SnP(3) which completes with x=0 the series Li(10+4x )Sn(2âx )P(6) of the fast lithiumâion conductors αâ and ÎČâLi(8)SnP(4) (x=0.5) and Li(14)SnP(6) (x=1). Synthesis, crystal structure determination by singleâcrystal and powder Xâray diffraction methods, as well as (6)Li, (31)P and (119)Sn MAS NMR and temperatureâdependent (7)Li NMR spectroscopy together with electrochemical impedance studies are reported. The correlation between the ionic conductivity and the occupation of octahedral and tetrahedral sites in a closeâpacked array of P atoms in the series of compounds is discussed. We conclude from this series that in order to receive fast ion conductors a partial occupation of the octahedral vacancies seems to be crucial
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[Ge<sub>2</sub>]<sup>4â</sup>Dumbbells with Very Short GeâGe Distances in the Zintl Phase Li<sub>3</sub>NaGe<sub>2</sub>: A Solid-State Equivalent to Molecular O<sub>2</sub>
The novel ternary Zintl phase Li3NaGe2 comprises alkali-metal cations and [Ge2]4â dumbbells. The diatomic [Ge2]4â unit is characterized by the shortest GeâGe distance (2.390(1)â
Ă
) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8âN) rule. Raman measurements support these findings. The multiple-bond character is confirmed by electronic-structure calculations, and an upfield 6Li NMR shift of â10.0âppm, which was assigned to the Li cations surrounded by the Ïâ
systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand-free dumbbell in Li3NaGe2, the Ï-âbonding py and pz orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled Ï-type bands of the neat solid Li3NaGe2 cross the Fermi level, resulting in metallic properties. Li3NaGe2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.O.P. acknowledges
support from a Marie SkĆodowska-Curie Individual Fellowship.
L.M.S. is further grateful to the Fonds der Chemischen Industrie
and the Studienstiftung des deutschen Volkes for her fellowships.
A.J.K. gratefully acknowledges funding from the Alfred Kordelin
Foundation and computational resources from CSC â the Finnish
IT Center for Science.This is the accepted manuscript. The final version is available at http://onlinelibrary.wiley.com/wol1/doi/10.1002/ange.201508044/abstract
Lithiumâion mobility in Li6B18(Li3N) and Li vacancy tuning in the solid solution Li6B18(Li3N)1âx(Li2O)x
All-solid-state batteries are promising candidates for safe energy-storage systems due to non-flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The hostâguest structure Li6B18(Li3N) comprises large hexagonal pores filled with urn:x-wiley:14337851:media:anie202213962:anie202213962-math-0001 Li7N] strands that represent a perfect cutout from the structure of α-Li3N. Variable-temperature 7Liâ
NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19â
kJâmolâ1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O
Superâionic conductivity in ÏâLi9TrP4 (Tr = Al, Ga, In) and lithium diffusion pathways in Li9AlP4 polymorphs
The use of pure and impure placebo interventions in primary care - a qualitative approach
Background: Placebos play an important role in clinical trials and several surveys have shown that they are also common in daily practice. Previous research focused primarily on the frequency of placebo use in outpatient care. Our aim was to explore physicians' views on the use of placebos in daily practice, whereby distinction was made between pure placebos (substances with no pharmacological effect, e.g. sugar pills) and impure placebos (substances with pharmacological effect but not on the condition being treated, e.g. antibiotics in viral infections or vitamins). Methods: We performed semi-structured interviews with a sample of twelve primary care physicians (PCPs). The interview addressed individual definitions of a placebo, attitudes towards placebos and the participants' reasons for prescribing them. The interviews were transcribed and analysed using qualitative content analysis. Results: The definition of a placebo given by the majority of the PCPs in our study was one which actually only describes pure placebos. This definition, combined with the fact that most impure placebos were not regarded as placebos at all, means that most of the participating PCPs were not aware of the extent to which placebos are used in daily practice. The PCPs stated that they use placebos (both pure and impure) mainly in the case of non-severe diseases for which there was often no satisfactory somatic explanation. According to the PCPs, cases like this are often treated by complementary and alternative therapies and these, too, are associated with placebo effects. However, all PCPs felt that the ethical aspects of such treatment were unclear and they were unsure as to how to communicate the use of placebos to their patients. Most of them would appreciate ethical guidelines on how to deal with this issue. Conclusions: Many PCPs seem to be unaware that some of the drugs they prescribe are classified as impure placebos. Perceptions of effectiveness and doubts about the legal and ethical aspects of the use of placebos by PCPs may discourage their application. Dissemination of guidelines and consensus papers may be one approach, but it has to be acknowledged that the topic itself is in conflict with the PCPs' perception of themselves as professional and reliable physicians
Fast Ionic Conductivity in the Most Lithium-Rich Phosphidosilicate Li14SiP6.
Solid electrolytes with superionic conductivity are required as a main component for all-solid-state batteries. Here we present a novel solid electrolyte with three-dimensional conducting pathways based on "lithium-rich" phosphidosilicates with ionic conductivity of Ï > 10-3 S cm-1 at room temperature and activation energy of 30-32 kJ mol-1 expanding the recently introduced family of lithium phosphidotetrelates. Aiming toward higher lithium ion conductivities, systematic investigations of lithium phosphidosilicates gave access to the so far lithium-richest compound within this class of materials. The crystalline material (space group Fm3m), which shows reversible thermal phase transitions, can be readily obtained by ball mill synthesis from the elements followed by moderate thermal treatment of the mixture. Lithium diffusion pathways via both tetrahedral and octahedral voids are analyzed by temperature-dependent powder neutron diffraction measurements in combination with maximum entropy method and DFT calculations. Moreover, the lithium ion mobility structurally indicated by a disordered Li/Si occupancy in the tetrahedral voids plus partially filled octahedral voids is studied by temperature-dependent impedance and 7Li NMR spectroscopy
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