Li Lattice Site Research Articles

Electronic structure investigation of intrinsic and extrinsic defects in LiF

A systematic study of geometries, formation energies, and electronic structures has been carried out for LiF considering monodoping with Mg and Ti at the interstitial, and lattice site positions, codoping in equal and different proportions, and vacancy defects in absence and presence of foreign elements using hybrid density functional. This study reveals that, both Mg and Ti, show preference for the Li lattice sites over interstitial sites. Li-poor condition is energetically more preferable over Li-rich condition, and codoping is found to be more stable over individual doping. Under this condition, formation of Li-vacancy in codoped system is found to be spontaneous. The presence of only Li vacancy results negligible changes on LiF electronic structure. Interestingly, in presence of Mg, and Ti, it plays an important role by modifying the band gap. Present results provide important insights to tune optical properties of LiF through the rational design of defect-controlled synthetic conditions.

New insights into Li distribution in the superionic argyrodite Li6PS5Cl.

By using temperature-dependent neutron powder diffraction combined with maximum entropy method analysis, a previously unreported Li lattice site was discovered in the argyrodite Li6PS5Cl solid-state electrolyte. This new finding enables a more complete description of the Li diffusion model in argyrodites, providing structural guidance for designing novel high-conductivity solid-state electrolytes.

Magnetic properties of LiNi0.5Mn0.47Al0.03O2 as positive electrode for Li-ion batteries

The layered LiNi0.5Mn0.47Al0.03O2 was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO2 structure. This substitution of Al for Mn promotes the formation of Li(Ni0.472+Ni0.033+Mn0.474+Al0.033+)O2 structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni2+ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni2+(3a)–Mn4+(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni2+ (S = 1), Ni3+ (S = 1/2) and Mn4+ (S = 3/2) spin-only values. Delithiation has been made by the use of K2S2O8. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni4+ in the high spin configuration, while Ni2+(3a)–Mn4+(3b) ferromagnetic pairs remain, as the Li+(3b) ions linked to the Ni2+(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn4+ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.

Different incorporation of Cu+ and Cu2+ in lithium tetraborate single crystals

The incorporation site of Cu in the scintillator and thermoluminescent dosimeter material lithium tetraborate Li2B4O7:Cu has been shown to depend on the charge state of the dopant. As confirmed by a refined analysis, the EPR spectra of an unpaired hole can be ascribed to Cu2+ situated near the Li lattice site with C1 symmetry, in contrast to the higher (C2) overall symmetry reported earlier for Cu+ in its relaxed excited state, the latter suggesting interstitial incorporation for the monovalent dopant. Consequences for charge transfer processes involving copper ions are discussed.

Investigation of Cu-doped Li2B4O7 single crystals by electron paramagnetic resonance and time-resolved optical spectroscopy

A low-temperature study of the thermoluminescent dosimeter material, lithium tetraborate(Li2B4O7) doped by Cu, has been carried out by the methods of electron paramagnetic resonance(EPR) and time-resolved polarization spectroscopy using 4–20 eV synchrotron radiation and1 µs Xe flash lamp pulses in the region 3–6 eV. The observed EPR spectra of an unpaired holewith strong d-character and characteristic hyperfine splittings can be ascribed toCu2+ substituted at a Li lattice site and displaced due to relaxation. The results on theCu+-related luminescence strongly support the conclusion about a low-symmetry position of copperimpurity ions in the lithium tetraborate lattice. The temperature dependence of the decay kinetics ofthe Cu+-related 3.35 eV emission indicates a triplet nature for the relaxed excited state of theCu+ centres. An off-centreposition of the Cu+ ion in the relaxed excited state is suggested.

EPR of Cu2+ in lithium tetraborate single crystals

AbstractA low temperature electron paramagnetic resonance study of single crystals of the scintillator and thermoluminescent dosimeter material lithium tetraborate (Li2B4O7) doped by Cu has been carried out. The observed spectra of an unpaired hole with strong d ‐character and characteristic hyperfine splittings can be ascribed to Cu2+ situated at or near the Li lattice site, which supports the conclusions of a parallel luminescence study about the low symmetry of emitting Cu+ sites. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Local Co structure and ferromagnetism in ion-implanted Co-dopedLiNbO3

A ferromagnetic oxide ${\mathrm{Co}}_{0.05}(\mathrm{LiNb}{)}_{0.95}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ was prepared by Co ion implantation into (104) ${\mathrm{LiNbO}}_{3}$ wafers. Co is uniformly distributed to a depth of $\ensuremath{\sim}220\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ by implanting at three different energies and doses. Electron energy loss spectroscopy and x-ray absorption near-edge structure (XANES) spectra reveal a solid solution of cobalt in an implanted layer, where Co is not metallic but in the 2+ state. Furthermore, full multiple-scattering ab initio calculations of Co XANES at the $K$ edge clearly provide a structure fingerprint to determine Co substitution at Li lattice sites rather than Nb. The ${\mathrm{Co}}_{0.05}(\mathrm{LiNb}{)}_{0.95}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ system exhibits room temperature ferromagnetism of $1.3{\ensuremath{\mu}}_{B}∕\mathrm{Co}$ ion with an easy in-plane axis and a high Curie temperature of $710\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

The 181Hf/181Ta Probe in the Li and Nb Sites of Congruent Linbo3 Co-doped with Mg and Cr Ions Studied by γ–γ PAC

The results reported in this work show the relevance of the lithium deficiency for the Li lattice site occupation of dopants in congruent lithium niobate crystals co-doped with 0.1 mol% Cr2O3 and different concentrations of HfO2, up to 3 mol%. The same behavior is observed in a crystal doped with 1 mol% of HfO2 and co-doped with 4 mol% MgO where after annealing most of the Hf/Ta probes occupy the Nb lattice site.

Lattice site location of ion-implanted Li8 in Silicon Carbide

The lattice sites of ion-implanted Li atoms in 6H-, 4H-, and 3C-SiC were studied. Radioactive Li8 ions (t1/2=0.84 s) were implanted with 60 keV into the crystalline SiC samples, and the channeling and blocking effects of 1.6 MeV alpha particles emitted in the decay were measured to determine the Li lattice sites. The alpha emission channeling spectra measured along different crystallographic directions reveal that Li occupies mainly interstitial sites with tetrahedral symmetry, centered along the c-axis atom rows in the hexagonal lattices. In the cubic 3C-SiC structure, Li is located on tetrahedral interstitial sites as well. For 6H-SiC, the implantation temperature was varied between 200 and 823 K without observing significant changes in the emission channeling spectra. Thus, Li diffusion or Li defect interaction resulting in a lattice site change does not occur in this temperature regime.

Influence of lithium niobate stoichiometry on the lattice position of Nd 3+ in Nd:LiNbO 3

In order to study the lattice position influence on the optical properties of the Nd 3+ doped LiNbO 3, the local order around neodymium ions has been investigated in a set of Nd-doped LiNbO 3, with different stoichiometries ([Li]/[Nb] ratios) by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The main position has been determined for this technologically important foreign ion to be inside the Li-octahedron and shifted 0.4 Å from the Li lattice site toward the structural vacancy. The host position is independent of the stoichiometry, but the arrangement of the nearest oxygen surrounding the foreign ion is different for such samples with different [Li]/[Nb] ratios.

Lattice site location studies of ion implanted Li8 in GaN

The lattice sites of ion implanted Li atoms in GaN were studied as a function of implantation temperature between room temperature and 770 K. We measured the channeling and blocking patterns of α-particles emitted in the radioactive decay of implanted Li8 ions to determine the Li lattice sites. Below 700 K Li atoms occupy mainly interstitial sites in the center of the c-axis hexagons at positions c/4 and 3c/4, where c is the lattice constant in c-axis direction. Around 700 K Li starts to diffuse and presumably interacts with vacancies created in the implantation process. This leads to the formation of substitutional Li above 700 K. An activation energy of about 1.7 eV for interstitial Li diffusion was determined.

Exafs study of the Nd ion lattice position in Nd:MgO: LiNbO3 and Nd:ZnO:LiNbO3

The local order around Nd3+ ions in Nd:MgO:LiNbO3 and Nd:ZnO:LiNbO3 codoped samples has been investigated by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Independently from the codoping atom, the main position of the Nd ions has been determined to be near the Li lattice site.

Li+ diffusion in the fast ionic conductor Li3N investigated by beta -radiation detected NMR

Applying the method of beta -radiation detected nuclear magnetic resonance/relaxation ( beta -NMR) to 8Li nuclei in 7Li3N single crystals comprehensive information on static and dynamic properties was obtained. Below T approximately=200 K the electric field gradients (EFG) at the two inequivalent Li lattice sites (Li(1), Li(2)) were determined. The spin-lattice relaxation (SLR) behavior above T approximately=300 K and the 8Li NMR signals in the extreme narrowing regime (T>or=500 K) could be attributed to interlayer diffusion involving Li+ jumps between Li(1) and Li(2) lattice sites ((1 to or from 2) jumps). In the temperature range 200 K<or=T<or=300 K the transients of the 8Li(1) and 8Li(2) polarizations were measured separately by applying a special radio frequency scheme. The different SLR behaviour allowed us to study the Li+ intralayer diffusion confined to the Li2N layers. Furthermore, ultra-slow interlayer (1 to or from 2) jumps with correlation times of up to 10 s were observed in this T region. Below 200 K a nonexponential 8Li polarization decay depending weakly on B and T was observed. The SLR in this T range is discussed in terms of statistically distributed relaxation centres.