Structural and Electronic Characterization of Eu2LiSi3, Eu2LiGe3 and EuxSr2−xLiGe3 Mixed Crystals
ABSTRACT The new rare earth metal Zintl phases Eu2LiSi3, Eu2LiGe3 and the solid solution EuxSr4−xLi2Ge6 have been synthezised by solid state inert gas techniques and their crystal structures been determined from single crystals. Eu2LiSi3 crystallizes in an own structure type which has close relations to the ThSi2 type with lithium being situated on silicon vacancies. This generates a new kind of planar Zintl anion which has an all trans linear chain backbone and terminal Si side groups at half of the silicon atoms of the chain. Eu2LiGe3 forms the −Ca2LiSi3 structure with an unbranched planar polymeric Zintl anion which has a cis-trans conformation of the kind (tttctc)n. Both of the polyanions [Si3]5− and [Ge3]5−, respectively are unsaturated with an underoccupied π* system leaving one residual π bond per three Tt atoms (Tt = Si, Ge). Features of the crystal and of the electronic structures are being analysed based on geometrical and on band structure considerations. DOS, partial DOS, Mulliken overlap populations and calculations of the electron localization function (ELF) based on Extended Hückel and on LMTO calculations confirm the bonding structure and reveal preferred localizations of the π bonds.
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ABSTRACT: The equilibrium lattice properties, electronic and optical properties of LiRE2Si3 (RE ¼ Nd, Sm, and Eu) compounds have been investigated. LiRE2Si3 compounds show strong absorption in the entire range of solar spectrum. The conversion efficiencies are 52.4, 70.2, and 63.9% for LiNd2Si3, LiSm2Si3, and LiEu2Si3, respectively. The efficiencies of LiSm2Si3 and LiEu2Si3 are about twice of GaAs (34%), and they are three times higher than Si (20%). The presence of 4f shell and the unoccupied p* states enhance the electron transportation invoked by photon adsorption. The LiRE2Si3 compounds are the excellent candidates of photovoltaic materials so far.Applied Physics Letters 07/2013; 103(1):013902. DOI:10.1063/1.4813013 · 3.52 Impact Factor
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ABSTRACT: BaLi1.09In0.91Ge2 is synthesized from a mixture of Ba, Li, In, and Ge in a ratio of 1:2:2:2 (Nb tube, 950 °C, 5 h) and characterized by single crystal XRD and TB-LMTO-ASA quantum chemical calculations.Bulletin- Korean Chemical Society 12/2013; 34(12). DOI:10.5012/bkcs.2013.34.12.3847 · 0.84 Impact Factor
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ABSTRACT: The ternary silicide La2Li2Si3 was synthesized from the elements in a sealed niobium tube. La2Li2Si3 was characterized by powder and single crystal X-ray diffraction: Ce2Li2Ge3 type, Cmcm, a = 450.03(8), b = 1880.3(4), c = 689.6(1) pm, wR2 = 0.0178, 597 F2 values, and 26 parameters. The La2Li2Si3 structure contains two crystallographically independent silicon sites, both in slightly distorted trigonal prismatic coordination. The Si1 atoms are located in condensed La6 prisms and form cis–trans chains (two-bonded silicon) with Si1–Si1 distances at 238 and 239 pm, indicating single bond character. The Si2 atoms are isolated within La2Li4 prisms. La2Li2Si3 might be formally considered as an electron precise Zintl phase with an electron partition (2La3+)(2Li+)(2Si12–)(Si24–). Electronic structure calculations show a trend in this direction based on a charge density analysis with large electron localization around the Si1–Si1 chains. The compound is found weakly metallic with chemical bonding reminiscent of LaSi and additional features brought in by Li and Si2. High resolution solid state 7Li and 29Si MAS-NMR spectra are in agreement with the crystal structural information, however, the 29Si resonance shifts observed suggest strong Knight shift contributions, at variance with the Zintl concept. Variable temperature solid state 7Li spectra indicate the absence of motional narrowing on the kHz timescale within the temperature range 300K < T < 400 K.ChemInform 03/2012; 14(3):367–374. DOI:10.1016/j.solidstatesciences.2011.12.012