Lithium insertion into In2S3 studied by perturbed γ-γ angular correlation

Li_xIn₂S₃ was electrochemically prepared with different small amounts x of lithium (0?x?0.13) in order to maintain the initial crystallographic structure of the thiospinel In₂S₃. About 10¹² radioactive ¹¹¹In ions have been implanted into these samples at 400 keV to perform PAC experiments in the temperature range from 10 to 773 K. The results are compared to previous experiments with undoped In₂S₃ samples. According to the structure of In₂S₃ in the β-phase, which belongs to the I4₁/amd space group having a unit cell with 32 In and 48 S atoms and the cell parameters α=7.61 Å and c=32.28 Å, three different electric field gradients were observed. Within two different temperature ranges dynamical EFGs occur, which are clearly influenced by the insertion of Lithium. The strong dependence of one EFG on the Li concentration x can be correlated to the effective charge of the In ions. This correlation is discussed with respect to XRD analyses of the Li_xIn₂S₃ samples and to XANES measurements on a similar sample.     

Self-organized layered hydrogenation in black Mg2NiHx switchable mirrors

In addition to a mirrorlike (Mg2Ni) and a transparent (Mg2NiH4) state, thin films of Mg2NiHx exhibit a remarkable black state with low reflection over the entire visible spectrum, essentially zero transmission and a low electrical resistivity. Such a black state is not explicable for a homogeneous layer since a large absorption coefficient always yields substantial reflection. We show that it results from a self-organized and reversible double layering of metallic Mg2NiH0.3 and semiconducting Mg2NiH4.     

Electronic Relaxation in Indium Oxide Films Studied with Perturbed Angular Correlations

The electronic relaxation due to the ¹¹¹In → ¹¹¹Cd electron capture process was studied by measuring perturbed γγ-angular correlations after ¹¹¹In-ion implantation into indium oxide films of various compositions and thicknesses and deposited on different substrates. X-ray diffraction, Rutherford backscattering and secondary ion mass spectrometry were used to characterize the microstructure and composition of the samples. The film thickness and type of substrate were found to have much less influence on the after effect than the deposition parameters and impurities.     

Lithium in In2S3

The electrochemical insertion of lithium into β-In₂S₃ at different concentrations has been investigated by means of γγ-Perturbed Angular Correlations measurements using implanted radioactive ¹¹¹In nuclei. The study of the hyperfine interactions of the ¹¹¹Cd nuclei during the decay ¹¹¹In(EC)¹¹¹Cd allowed to determine the evolution of the three observed electric field gradients at different temperatures and lithium contents. This study reveals a great difference of behavior between the three indium sites of the structure, and shows the mobility of indium ions and their partial reduction after lithium insertion. In₂S₃ is good model material to study the properties of more complex materials based on this structure, which may be used as electrodes for lithium-ion batteries. This revised version was published online in September 2006 with corrections to the Cover Date.     

The fragile magnetic structures of Fe/CeH2−δ multilayers

Fe/CeH_2−δ multilayers exhibit at room temperature evidence of interlayer exchange coupling. Subsequent Fe layers are either parallel or antiparallel to each other, depending on the Fe and CeH_2−δ layer thickness. However, when both layers have thickness larger than 15 Å, the antiferromagnetic structure becomes fragmented into domains laterally limited to a few microns, and the magnetic structures become very fragile. Small magnetic fields of a few Oersteds acting on the samples during growth induce helimagnetic configurations which coexist with antiferromagnetic coupling. The magnetic structures can be permanently destroyed by applying magnetic fields larger than 150 Oe.     

Structural and magnetic properties of La/Fe multilayers

The structural and magnetic properties of La/Fe multilayers were investigated by X-ray diffraction, RHEED, magnetometry and⁵⁷Fe Mössbauer spectroscopy. Comparison is made with previous results obtained for Ce/Fe multilayers. Remarkably sharp interfaces are found, with roughness between 2 and 2.5 Å. The magnetic interface in the Fe sublayers resulting from the distribution of magnetic hyperfine fields distinctly exceeds the extension of the structural interface and points to a magnetic proximity effect. This is discussed in relation to a strong 3d-5d hybridization recently found in measurements of magnetic circular X-ray dichroism. Both the structural and magnetic La/Fe interface is less extended than the interface in Ce/Fe multilayers. Below a thickness of about 25 Å, the individual Fe layers grow in an amorphous structure on the La layers. In this case, Curie temperatures are below 200 K and the Fe-layer saturation magnetization is reduced up to 50%, and there is evidence of a non-collinear spin structure. It is argued that this mainly reflects the properties of pure amorphous Fe.     

Lattice Location Studies of Indium in Cr2O3

The lattice sites of implanted In atoms in Cr₂O₃ were investigated by means of electron emission channeling (EC) measurements using ¹¹¹In probe atoms. EC spectra were recorded for several axes and compared to simulations. Indium atoms are most likely located at near-Cr sites. Small differences in the EC patterns for prompt and delayed electrons may be an indication for displacements of ¹¹¹Cd emitter atoms following the electron capture decay of In. This revised version was published online in September 2006 with corrections to the Cover Date.     

Magnesium imide: synthesis and structure determination of an unconventional alkaline earth imide from decomposition of magnesium amide

Magnesium imide (MgNH) was produced by monitoring the decomposition process of magnesium amide with in situ neutron diffraction. Significant changes in the structure of magnesium amide are detected during heat treatment and eventually result in the formation of crystalline MgNH. A model for the crystal structure of magnesium imide (MgNH) is presented for the first time. Remarkably, magnesium imide offers unique structural features similar to the cyclosilicate class and can be described as a porous solid formed by a sequence of linked chains of face sharing Mg(6)N(6) hexagonal prism clusters.     

Altered thermodynamic and kinetic properties of MgH(2) infiltrated in microporous scaffold

MgH(2) nanoparticles with a size of <3 nm were formed by direct hydrogenation of Bu(2)Mg inside the pores of a carbon scaffold. The activation energy for the dehydrogenation was lowered by 52 kJ mol(-1) compared to the bulk material, and a significantly reduced reaction enthalpy of 63.8 ± 0.5 kJ mol(-1) and entropy (117.2 ± 0.8 J mol(-1)) was found for the nanoconfined system.