Lithium aluminum oxide (γ-LiAlO 2 ) has been discussed and used for various applications, e.g., as electrode coating, membrane, or tritium breeder material. Although lithium-ion diffusion in this solid is essential for these purposes, it is still not sufficiently understood on the microscopic scale. Herein, we not only summarize and assess the available studies on diffusion in different crystalline forms of γ-LiAlO 2 , but also complement them with tracerdiffusion experiments on (001)-and conductivity spectroscopy on (100)oriented single crystals, yielding activation energies of 1.20(5) and 1.12(1) eV, respectively. Scrutinous crystal-chemical considerations, Voronoi− Dirichlet partitioning, and Hirshfeld surface analysis are employed to identify possible diffusion pathways. The one-particle potential, as derived from hightemperature powder neutron diffraction data presented as well, reveals the major path to be strongly curved and to run between adjacent lithium positions with a migration barrier of 0.72(5) eV. This finding is substantiated by comparison with recently published computational results. For the first time, a complete model for lithium-ion diffusion in γ-LiAlO 2 , consistent with all available data, is presented.
The local structure and mobility of lithium ions of the NASICON-type ionic conductor Li 1+x Al x Ti 2−x (PO 4 ) 3 (with x = 0.0, 0.1, 0.2, 0.35, 0.5, 0.7 and 1.0), synthesized using conventional solid-state reaction route have been studied with solid-state nuclear magnetic resonance (NMR) techniques. 6 Li, 7 Li, 27 Al, and 31 P solid-state NMR experiments have been employed to trace the structural changes with varying cation concentration. The structural evolution and the creation of new Al and P environments with changing cation contents were studied by magic-angle spinning (MAS) NMR measurements. 6 Li MAS NMR and 27 Al triple-quantum MAS (3QMAS) show high-resolution spectra enabling site assignments and phase-purity inspections. The temperature dependences of 7 Li NMR spin−lattice relaxation (SLR) rates for different compositions yield important information on the lithium ion mobility in the systems. Li ion jump rates, the activation energies, and the dimensionality of Li diffusion were deduced from the SLR experiments. A vacancy migration model has been proposed for the Li + ionic diffusion process in pure-phase Li 1+x Al x Ti 2−x (PO 4 ) 3 prepared by solid-state reaction. Above a certain threshold value of x (0.5) additional phosphate phases appear that slows down diffusion. This phenomenon can be observed from 6 Li exchange spectroscopy. The optimum cation concentration for maximum ionic mobility in the phase-pure Li 1+x Al x Ti 2−x (PO 4 ) 3 system can be read directly from the solid-state NMR results.
Ternary semiconductor nanocrystals, such as CuInSe2 , are of high interest for photovoltaic application due to their relatively low toxicity and unique properties. During the last decades great success has been achieved in the colloidal synthesis of binary nanoparticles, but for ternary compounds this research is still in an early stage of development. These materials are a challenge for synthetic chemistry, because the interaction between the three components (copper, indium, and selenium) plays a major role for the production of high quality material. The purpose of this Minireview is to provide a summary of the achievements in colloidal synthesis of CuInSe2 nanoparticles--in particular, details of reaction mechanism and its characterization possibilities, which might be useful also for the colloidal synthesis of other multicomponent systems.
This article reports on Li self-diffusion in lithium containing metal oxide compounds. Case studies on LiNbO 3 , Li 3 NbO 4 , LiTaO 3 , LiAlO 2 , and LiGaO 2 are presented. The focus is on slow diffusion processes on the nanometer scale investigated by macroscopic tracer methods (secondary ion mass spectrometry, neutron reflectometry) and microscopic methods (nuclear magnetic resonance spectroscopy, conductivity spectroscopy) in comparison. Special focus is on the influence of structural disorder on diffusion.
Nearly monodisperse lead chalcogenide (PbE, E = S, Se, or Te) semiconductor quantum dots of controllable shape have been produced via a novel synthesis which includes the occurrence of in situ formed Pb(0) particles. Tunable size and shape are achieved through appropriate choice of the precursor type and the stabilizer. As precursor, we use, on the one hand, lead oxide or lead acetate, on the other hand, tellurium, selenium, or sulfur powder dissolved in trioctylphosphine (TOP), tributylphosphine (TBP), or 1-octadecene (ODE). Oleic acid (OA) and various amines, as well as TOP and TBP are used for stabilization. With respect to possible application in hybrid solar cells, the surface of as-synthesized spherical PbSe nanocrystals was investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS) and thermogravimetric analysis (TGA). As an important result, it was found that the surface is not mostly covered by oleic acid after synthesis, but by a phosphorus compound. We also applied a ligand exchange procedure with hexylamine and found evidence for the successful attachment of hexylamine to the nanocrystal surface. Additionally, charge separation between these nanoparticles and the conjugated polymer poly(3-hexylthiophene) (P3HT) is studied by electron spin resonance and photoinduced absorption spectroscopy. The spectra obtained suggest that charges can be produced successfully by photoinduced charge transfer.
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