Li-doped Sample Research Articles

Boosted visible light dye-decontamination and colossal dielectric constant features of Bi2O3: Role of In, Cu and Li-dopants

This study focused on improving the optical, dielectric properties, and photocatalytic efficiency of Bi2O3, a prominent photocatalyst with challenges like limited visible light absorption and rapid electron-hole pair recombination. Using an adapted sol-gel technique, pure Bi2O3, In, Cu and Li-doped Bi2O3 visible-light-driven photocatalyst were synthesized. X-ray diffraction (XRD) confirmed monoclinic Bi2O3 formation. The inclusion of In, Cu, and Li ions into the Bi2O3 lattice was evidenced by alterations in diffraction peak intensities, lattice parameters, and changes in average crystallite size. Vibrational spectra corroborated the formation of pure α-Bi2O3 with slight shifts in transmittance bands, aligning with the XRD findings. Morphological investigation via scanning electron microscopy (FE-SEM-EDX) confirmed the purity of the synthesized nanocompositions and unveiled that the doping induces distinct morphological changes in Bi2O3 nanoparticles, resulting in increased porosity and formation of round and needle-like shapes (In-doped), coalescence of particles (Cu-doped), and fused agglomerates with altered particle size distribution (Li-doped). Optical analysis demonstrated a red shift in the band gap energy of α-Bi2O3 (initially 2.90 eV), with In, Cu, and Li doping, resulting in band gaps of 2.77 eV, 2.78 eV, and 2.88 eV, respectively, accompanied by high refractive indices exceeding 2.0, rendering them suitable for optical applications. Both Cu and Li doping led to enhanced relative permittivity (εʹ) values, with the Li-doped sample displaying remarkable εʹ values at low frequencies (up to 1000 Hz). The In, Cu and Li doping has the effect of reducing PL (photoluminescence) emission intensity while simultaneously diminishing radiative recombination and promoting the separation of photogenerated charge carriers. The doped samples demonstrated superior degradation performance, with In-doped and Cu-doped samples achieving degradation efficiencies of 99% and 91%, respectively, within 180 min. This remarkable performance can be attributed to their visible-light-responsive band gaps, increased electron-hole trapping sites, and distinct morphological features.

Effects of lithium content on the electrochemical performance of Li1+xV3O8 cathode materials for lithium-ion batteries

Lithium trivanadate (LiV3O8) is of great interest due to its large capacity, low cost and easy preparation. However, it still suffers from an inferior cyclability and rate capability. To solve these shortcomings of LiV3O8, a small extra amount of lithium was introduced into Li sites of LiV3O8. Herein, Li-doped LiV3O8 (Li1+xV3O8) materials were prepared and the electrochemical performance of Li1+xV3O8 changes with x from 0 to 0.1, 0.2 and 0.3. The discharge capacity of Li1+xV3O8 increases from x = 0 to 0.2 and then decreases, and the change trend of cycle performance is the same as that of discharge capacity. The optimal Li-doped LiV3O8 sample, Li1.2V3O8, exhibits much higher capacity and better cyclability and rate capability than LiV3O8. Galvanostatically discharged and charged between 2.0 and 4.0 V, Li1.2V3O8 and LiV3O8 present the initial discharge capacities of 305 and 268 mAh g−1 at 0.1 C (30 mA g−1), respectively, and the corresponding capacity retentions are 87% and 80% after 50 cycles. Even at a high current rate of 2 C, Li1.2V3O8 exhibits high discharge capacity of 173 mAh g−1, much higher than the discharge capacity of 133.6 mAh g−1 for LiV3O8. The better electrochemical performance of Li1.2V3O8 can be ascribed to the doping of appropriate amount of Li+ in LiV3O8 and the resulted higher diffusion coefficients of Li+ in Li1.2V3O8.

Effect of dopants on the electrocaloric effect of 0.92 Pb(Mg1/3Nb2/3)O3–0.08 PbTiO3 ceramics

This paper presents an extract of modifications of lead magnesium niobate–lead titanate in order to optimize its electrocaloric properties. Electrocaloric entropy (ΔSEC) and temperature changes (ΔTEC) are measured in a temperature range from −5°C up to 100°C using differential scanning calorimetry. The influence of dopants (Li+, Mn2+, Sr2+, Ta5+) on the electrocaloric effect as well as on microstructure, dielectric and ferroelectric behavior is investigated. The maximum of relative permittivity can be shifted to lower or higher temperatures depending on the added dopant and decreased ferroelectric hysteresis losses were observed for all altered compositions. For the undoped PMN–8PT ceramics maximum ΔTEC of 0.58K and ΔSEC of 0.51Jkg−1K−1 were measured, when applying an electric field of 2kVmm−1 at 30°C. The electrocaloric temperature change showed lower values for all doped PMN–8PT. Remarkably, this is accompanied with an increase of the entropy change for the Li-doped sample.

Doping of C70 fullerene peapods with lithium vapor: Raman spectroscopic and Raman spectroelectrochemical studies

Raman spectroscopy and in situ Raman spectroelectrochemistry were applied to study the lithium vapor doping of C70@SWCNTs (peapods). A strong degree of doping was proved by the vanishing of the single walled carbon nanotubes (SWCNT’s) radial breathing mode (RBM) and by the attenuation of the tangential (TG) band intensity. In contrast to potassium vapor doping, the strong downshift of the frequency of the TG band has not been observed for Li-doping. The Li vapor treated peapods remained partly doped even if they were exposed to humid air. This has been reflected by a reduced intensity of the nanotube and the fullerene modes and by the change of the shape of the RBM band as compared to that of the undoped sample. The modes of the intratubular fullerene were almost unresolved after the contact of the Li-doped sample with water. A lithium insertion into the interior of a peapod and its strong interaction with the intratubular fullerene is suggested to be responsible for the air-insensitive residual doping. This residual doping was studied by spectroelectrochemical measurements. The TG band of the Li doped peapods is partly upshifted during the anodic doping, which points to the different state of C70@SWCNTs and C60@SWCNTs studied previously.

Synthesis and Luminescence Properties of Non-Doped Long Persistent Phosphors : Mg<sub>2</sub>SnO<sub>4</sub>

A white long persistence phosphor was synthesized in a single-phase of Mg2SnO4 which was synthesized by a solid-state reaction. This phosphor crystallized in an inverse spinel structure and showed a broad-band emission from 350nm to 700nm. The afterglow was observed upon the excitation by 254nm. A Li-doped Mg2SnO4 sample showed a higher photoluminescence intensity and a longer lifetime than the non-doped one.

Magnetic and Mössbauer studies on nanocrystalline Co1−x Li x Fe2O4 (x = 0, 0.2)

Ultrafine particles of Co1 − x Li x Fe2O4 (x = 0, 0.2) samples are prepared by glycine–nitrate combustion route. X-ray diffraction and transmission electron microscopy studies show that the samples have cubic spinel structure and average crystallite sizes of x = 0 and 0.2 are 36 and 44 nm respectively. Vibrating sample magnetometer studies revealed the ferromagnetic nature of the samples. Li-doped CoFe2O4 sample showed higher values of coercive field, remanent magnetization and saturation magnetization compared to pure CoF2O4 indicating the enhancement of magnetic interactions. Mossbauer spectra at 77 K exhibited two broad sextets indicating that Fe3 + ions occupy both tetrahedral and octahedral sites. From these studies, it is concluded that Co1 − x Li x Fe2O4 (x = 0, 0.2) samples exhibit an inverse spinel structure. At room temperature, two sextets are superimposed on a very broad non-Lorentzian background indicating the presence of superparamgnetic fraction in agreement with the microscopic observations.

Flux pinning and magnetic relaxation in melt-processed YBa2Cu3O7−δ doped with Li

Melt-processed samples of YBa2Cu3O7−δ (YBCO) doped with Li additions substituting at Cu(2) plane sites were used to study the effects of doping on the superconducting temperature, critical current density, irreversibility field, upper critical field, coherence length, and magnetic relaxation as a function of temperature and magnetic field. The intrinsic superconducting properties were found only slightly influenced by Li additions at some optimal concentration (0.6at.%). At this Li concentration the volume pinning force of doped material is about five times that of undoped YBCO in intermediate magnetic fields at 77K. No significant change of the maximum volume pinning force with oxygen defects after long-time oxygenation experiment (∼450h) has been observed. The normalized pinning force of the sample optimally doped with Li obeys the same scaling law as a function of magnetic field and temperature before and after additional heat treatment, indicative of a single type of pinning centers. The time dependence of the magnetization in the standard and in the Li-doped sample has been analyzed in the framework of collective pinning theory. The magnetic relaxation measurements combined with the B-T phase diagram data provide evidence of an elastic-plastic transition. The pinning parameters estimated show a considerable enhancement of the critical current density in the optimally doped sample, but only an insignificant change in the effective activation energy, pointing to a weak pinning of pointlike pinning centers, created by Li additions.

Li- and Mg-doping into icosahedral boron crystals, α- and β-rhombohedral boron, targeting high-temperature superconductivity: structure and electronic states

The possibility of high T C superconductivity is suggested for lithium- and magnesium-doped icosahedral boron crystals, α- and β-rhombohedral boron. The doping of these elements was attempted by a vapor diffusion processing. Both lithium and magnesium are hardly doped into the α-rhombohedral boron, although small amounts of metallic parts are found in the sample. In only one Li-doped sample, the metallic part contained 0.02 vol% of the superconductive phase ( T C∼36 K). Magnesium was successfully doped into β-rhombohedral boron homogeneously up to 4 at% (Mg 4.1B 105), although considerable amount of impurity silicon was introduced together with magnesium. The structures of the doped samples were analyzed assuming co-doping of magnesium and silicon. The relation between the site occupancies of the dopants and the lattice expansion is discussed. The estimation of the density of states near the Fermi energy by EELS and magnetic susceptibility measurements suggested a metal transition of the β-rhombohedral boron by the doping of magnesium and silicon. The relation between the metal transition and the intrinsic acceptor level is also discussed.

Ferromagnetic and ferroelectric behaviors of A-site substituted YMnO3-based epitaxial thin films

Dielectric and magnetic properties of A-site substituted YMnO3 epitaxial films were studied. Stoichiometric epitaxial YMnO3 films clearly show ferroelectric behavior in P–E and C–V measurements. The I–V property is well explained by the Pool–Frenkel-type carrier emission with p-type conduction due to the existence of Mn4+, and the activation energy is calculated to be 0.58 eV. The leakage current decreases by substituting Y for Zr and increases by Li or Mg substitution. Although YMnO3 films exhibit antiferromagnetic magnetization behavior regardless of the crystallographic orientation and the carrier concentration, Li-doped sample displays parasitic ferromagnetic behavior (weak ferromagnetism). Substituting Y for Yb enhances the ferromagnetic interaction.

Melt-textured YBa 2Cu 3O 7 based material doped with Li: high trapped fields and pinning

The pinning forces and trapped fields obtained in bulk YBa 2Cu 3O 7 based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K. The measurements of the magnetic relaxation at a field of 1 T reveals that the activation energy above 65 K is higher for the Li-doped sample indicating that Li impurities are more effective in increasing the pinning energy.

Melt-textured YBa2Cu3O7 based material doped with Li and Zn: Comparison of high trapped fields and pinning

The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K.

Correlation of Li ion and the environmental elements in the surface nano-reaction field of polyacenic semiconductive material as the battery electrode

The correlation of lithium ion and other elements at the surface of the battery electrode made of polyacenic semiconductive (PAS) material film is discussed focusing on the passivation-layer formation. Behavior of these elements in the passivation layer of the Li-doped PAS films at several stages of doping were examined by the depth-profiling technique of X-ray photoelectron spectroscopy (XPS) together with the Li-doped graphite film sample for the reference. A certain different nature of the doped Li ion (Li δ+) and carbanion (C δ−) between the PAS and graphite films has been revealed. It was concluded that the PAS material film possesses certain surface nanopores or nano-reaction fields to accommodate the passivation species near its surface, being completely different from the graphite film.

Alkaline-Metal Doped MoO3/TiO2Systems: Structure of Supported Molybdates

The structure of molybdenum oxocompounds formed in TiO2-supported MoO3systems doped with alkaline metals have been studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) and X-ray absorption (XAS) spectroscopies. XRD, FT-IR, and XAS data give a detailed picture of the structure of molybdenum oxocompounds formed in these systems. Mo atoms are mostly octahedrally coordinated in an undoped TiO2support, as a dispersed MoO3phase. However, a high fraction of molybdenum cations are in tetrahedral coordination after the addition of Li, Na, or K as dopants. Thus, only MoO42− species exist in the 1 wt% Li-doped sample in the form of crystalline Li2MoO4, while tetrahedrally and octahedrally coordinated molybdenum form dispersed Mo2O72− chains in the 1 wt% Na- and K-doped systems. Octahedral polymolybdates, Rb2Mo3O10ċH2O and Rb2Mo4O13, whose structures are based in ‘MoO6’ units forming chains, are the species detected in the 1 wt% Rb-doped sample. Increasing the molybdenum content in K-doped samples favors formation of octahedral species, although in this case the structure of the supported phase is affected by the impregnation steps during the preparation of the sample.

Raman scattering and the evolution of polar order in Li-doped and Nb-doped KTaO3.

A comparative study of first-order Raman scattering in ${\mathrm{K}}_{0.984}$${\mathrm{Li}}_{0.016}$Ta${\mathrm{O}}_{3}$ and K${\mathrm{Ta}}_{0.976}$${\mathrm{Nb}}_{0.024}$${\mathrm{O}}_{3}$ single crystals has been performed. The soft-phonon line shows marked differences in the two systems, revealing a distinctive behavior with regard to the scale of polar order. Analysis of the low-frequency spectrum allows for an estimate of the polar correlation length in the Li-doped sample; this is limited to the nanometric scale, in agreement with the view of a dipole-glass transition. No evidence of a similar situation is found in the Nb-doped sample, where the general trend of soft-mode frequencies and intensities suggests a transition to a state of long-range order, for the quoted concentration. The intensities of the hard-phonon spectra and the T${\mathrm{O}}_{4}$ linewidth are shown to confirm the different evolution of the polar transition in the two systems.

The Effects Of Substitutional Alkaline Metals In Zinc Vacancy Of Zincselenide Single Crystals Grown By The Sublimation Method

AbstractThe photoluminescence measurements of alkaline metal doped zincselenide (ZnSe) single crystals were carried out to investigate how the impurity atoms substitute the intrinsic vacancy. Sample are grown by the sublimation method and the Li and Na with the concentrations of 0.1, 0.25 and 0.5 mol% were incorporated simultaneously. In the PL spectra with lower impurity concentrations, bound exciton lines of deep acceptor and donor-acceptor pair (DAP) bands were clearly observed accompanied by a weak free exciton line. Although the bound exciton lines becomes smaller with increasing the impurity concentration, the DAP band remains strong and its peak energy shift to lower energy side with the concentration. The decrease of the bound exciton lines is drastic for Li-doped sample than Na-doped sample. This indicates that Li atoms more easily occupy the Zn vacancies than Na.

The polar transition of Li-doped and Nb-doped KTaO3: Comparative analysis from hard-phonon raman spectra

Abstract Raman investigations have been performed on K0.984Li0.016TaO3 and KTa0.976Nb0.024O3 single crystals, in order to follow the peculiarities of non-ferroelectric phonons, which may be indicative of a different evolution of microscopic order during the polar transition. Specific features in the Nb case confirm a ferroelectric behaviour, whereas in the Li-doped sample the results are in agreement with a dipole glass transition.

Electrical Properties of Pyrolyzed and Electrochemically Lithium-Doped Poly(hydrazocarbonyl-1,4-phenylenecarbonyl) Film

The carrier transport and detailed carbonization processes of pristine (poly (hydrazocarbonyl-1,4-phenylenecarbonyl):PHP) film have been investigated as a function of heat-treatment temperature (HTT). Formation of (poly(1,3,4-oxadiazole-2,5-diyl-1,4-phenylene):POP) at HTT=400°C is confirmed and explained by the dehydration reaction of PHP molecular structure. Conductivity (σ) increases by 20 orders of magnitude from 10-18 S/cm with HTT of 1000°C. The enhancement of σ with HTT up to 600°C has been interpreted by the increase of localized charge carrier and the most prominent effect of the enhancement of σ by HTT above 800°C has been explained by not only the increase of carrier density but also the increase of mobility. Even in the sample of low HTT ( <500°C), σ is enhanced and its activation energy decreases upon electrochemical Li doping. On the other hand, in the sample of high HTT ( 800–1000°C) σ decreases slightly and its activation energy increases. Electrical conduction in the sample of low HTT ( <600°C) is explained by three-dimensional variable range hopping (3D-VRH). On the other hand, in the nondoped and Li-doped sample of high HTT ( ≥600°C), the conduction process is explained by taking both 3D-VRH and metallic conduction processes into consideration.

Growth of Li-doped and dopant-free Bi-Sr-Ca-Cu-O superconducting whiskers

The effects of dopant, Li, Na, K, Ga, Ge, Sb and Te, on the growing conditions and superconductivity in Bi-Sr-Ca-Cu-O whiskers have been examined and compared with dopant-free whiskers, synthesized by heating a glassy melt-quenched plate in a stream of O 2 gas. Every whisker has the 2212 structure as its main phase and a small amount of the 2223 phase, so that two resistance drops are observed in the R-T curve. Only Li is effective for increasing the T c of both the 2212 and the 2223 phase, and the T c's are enhanced with increasing Li content in the whiskers. The onset temperatures of Li-doped whiskers for the 2212 and 2223 phases are higher than those of the other samples by about 10 K and 6 K respectively. The T c,zero has a good correlation with the lattice parameter c of the 2212 phase. The length of the c-axis of the Li-doped sample is about 0.1 Å longer than that of the other samples. A T c,zero value of 107 K is obtained and a T c,zero of 112 K is indicated for the 2223 phase by extrapolation of the R-T curve in the Li-doped whiskers. A J c of 34 000 A/cm 2 at 77 K and 300 000 A/cm 2 at 66 K in a zero magnetic field have been obtained for the Li-doped whisker. The J c decreases steeply in magnetic field above 0.2 T at 77 K, and an anisotropy of the J c value of samples in a magnetic field has been observed.

GeO2 vs SiO2: Glass transitions and thermodynamic properties of polymorphs

Relative-enthalpy measurements have been made on the hexagonal, tetragonal, glass and liquid phases of GeO2. The glass transition is very sensitive to the impurity content, with a Tg ranging from 980 K for a pure product to 780 K for a Li-doped sample with 0.06 mol % Li. The relative Cp change at Tg of about 5% increases with the impurity content as a result of lower glass transition temperatures. Above 298 K the derived heat capacities are similar for all forms, with slightly higher values for the amorphous phases and two Cp cross-overs at 400 and 1000 K between the hexagonal and tetragonal modifications. For both GeO2 and SiO2 the coordination state markedly affects Cp and the entropy below 300 K, where the properties are much lower for the tetragonal than for the hexagonal modifications, i.e., S298 = 39.7 vs 55.3 J/mole K and 27.8 vs 41.4 J/ mole K for GeO2 and SiO2, respectively. The high-temperature Cp's of coesite and stishovite are likely similar to those of the low-pressure SiO2 forms. Finally, these results, low-temperature Cp data and enthalpy-of-solution measurements have been used to derive a consistent set of thermodynamic properties for the GeO2 modifications.

Thermal Expansion Behavior of Pure and Doped Cordierite by Time-of-Flight Neutron Diffraction

AbstarctIn order to reveal the mechanism of the negative c-axis expansion in cordierite (4 MgO 4 Al2O3 10 SiO2), the thermal expansion of cordierite containing small amounts of Cs, Li, B, Ge, Sc and Ni-cations was investigated by time-of-flight neutron diffraction at temperatures between 22 and 750°C. The samples were prepared by melting the constituent oxides followed by quenching and devitrification to obtain the hexagonal form (Indialite). Using the neutron powder diffraction data, the atom positions in the space group P6/mcc were refined by Rietveld least squares analyses.The expansion behavior of the cordierite structure could be explained in terms of the various kinds of constraints and the interatomic bond strengths of the structure. It was found that cordierite doped with Cs-cations shows the largest volume expansion, followed by the Li-doped sample. So-doped cordierite has the lowest volume expansion. All cordierite samples show positive expansion along the a-axis and negative expansion along the c-axis, except the Cs-doped sample which has positive expansion in both directions.