Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ 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(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)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.     

Spin-spin interaction of Ni2+ ions in ZnSiF6·6H2O

The angular dependences of the electron spin resonance spectrum of 1% Ni²⁺ ions in a ZnSiF₆·6H₂O matrix are investigated experimentally at 36 GHz and 4.2 K. Besides the main spectrum of the isolated ion, we observed a spectrum due to interacting pairs of Ni²⁺ ions, located in the first (nn) and second (2n) coordination spheres and coupled by, besides the magnetic dipole-dipole interaction, isotropic exchange: J _nn = (−197±1)×10⁻⁴, J _2nα = (−5±1)×10⁻⁴, and J _2nβ = (3±2)×10⁻⁴ cm⁻¹. Lines due to other isolated Ni²⁺ ions, which have a different initial splitting D, are also present in the spectrum with intensity comparable to the pair spectrum. Low-symmetry distortions of the crystal field are observed, caused by a pair of impurity ions located close to one another. It is shown that the previously proposed interpretation is incorrect. Fiz. Tverd. Tela (St. Petersburg) 41, 1602–1608 (September 1999)     

A New Highly Sensitive and Selective Fluorescent Cadmium Sensor

Condensation product (L) of salicylaldehyde and semicarbazide behaves as a fluorescent sensor for Cd²⁺ ion, in 1:1 DMSO:H₂O, over Mn²⁺, Fe²⁺, Ni²⁺, Co²⁺, Cu²⁺, Pb²⁺ and Hg²⁺ ions. The emission peak of L at λ_max = 520 nm, on excitation with 420 nm wavelength photons, showed an enhancement in intensity of ca 60-fold when interacted with Cd²⁺ ion. The intensity was however found to remain unaltered when interacted with metal ions—Mn²⁺, Fe²⁺, Ni²⁺, Co²⁺, Cu²⁺, Pb²⁺ and Hg²⁺. The intensity increases by approximately 20 fold on interaction with Zn²⁺ ion. The increase in the fluorescent peak can be explained on the basis of photo induced electron transfer (PET) mechanism. A 1:1 complexation between Cd²⁺ and L with log β = 4.25 has been proved.     

Stoichiometry of LiNiO2 Studied by Mössbauer Spectroscopy

From the ⁶¹Ni and ⁵⁷Fe Mössbauer spectroscopy data follows the cationic site assignment in Li_1–x Ni_1+x O₂. Our data explain the ferromagnetic properties of this material because of the appearance of Ni²⁺ (S=1) among Ni³⁺ (S=1/2) in Ni³⁺O₂ hexagonal planes. We have no evidence for the ferromagnetic interaction between the NiO₂ layers through the excess Ni²⁺ ions substituting the Li⁺ ions. The presence of Ni²⁺ found in the Ni³⁺O₂ planes explains the absence of the Jahn–Teller distortions probably because of the electronic transfer between the Ni³⁺ and Ni²⁺ ions.     

Effect of doping on the magnetic properties of the low-dimensional antiferromagnet CuO

The effect of doping with Li⁺, Zn²⁺, Ni²⁺, and Ga³⁺ ions on the magnetic susceptibility of the low-dimensional antiferromagnet CuO (T _N=230 K) has been studied within a broad temperature range of 77–600 K. The solubility of impurity ions in the CuO lattice is low, ⩽3%. Impurity ions, similar to intrinsic defects, distort antiferromagnetic coupling and can shift the long-and short-range magnetic-order regions toward lower T. Fiz. Tverd. Tela (St. Petersburg) 40, 1876–1880 (October 1998)     

Comparative study of crystal field effects for Ni ion in LiGa5O8, MgF2 and AgCl crystals

Exchange charge model (ECM) of crystal field was used to calculate the crystal field parameters (CFPs) and model the energy levels for Ni²⁺ ion in LiGa₅O₈, MgF₂ and AgCl crystals. Calculated energy levels (including splitting of the orbital triplets) are in good agreement with experimental absorption spectra. Covalent effects were shown to play an important role in all considered crystals. Bilinear forms built up from the overlap integrals between (Ni²⁺-Cl⁻)→(Ni²⁺-O²⁻)→(Ni²⁺-F⁻) pairs were considered a quantitative measure of the covalent (nephelauxetic) effects.     

An NBD-based Sensitive and Selective Fluorescent Sensor for Copper(II) Ion

A new 7-nitrobenz-2-oxa-1,3-diazole (NBD) derived fluorescent probe (1) exhibiting high selectivity for Cu²⁺ detection, produced significant fluorescence quenching in the presence of Cu²⁺ ion, while the metal ions Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ produced only minor changes in fluorescence. The apparent association constant (K _a) for Cu²⁺ binding in chemosensor 1 was found to be 1.22 × 10³ M⁻¹. The maximum fluorescence quenching activity caused by Cu²⁺ binding to 1 was observed over the pH range 6–10.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Spectroscopic studies of Ni2+ in calcium tartrate tetrahydrate

The optical absorption spectrum of a single crystal of calcium tartrate tetrahydrate, doped with Ni²⁺ ions, is investigated at laboratory and liquid nitrogen temperatures. From the analysis of the unpolarised and polarised spectra, the site symmetry of the Ni²⁺ ion is attributed to an elongated octahedron with a small tetragonal (C_4v) distortion.The analysis results in the following crystal field parametersB=875 cm^–1,C=3980 cm^–1,Dq=900 cm^–1, Dt=32cm^–1.The authors wish to express their thanks to the Head of the Department of Physics, I.I.T., Madras for providing the facilities to conduct experiments on a Cary-14 spectrophotometer. They wish to express their thanks to Prof. S.Radhakrishna (I.I.T., Madras) and Prof. S.V. J.Lakshman (S.V. University) for thier interest in the work. The authors are grateful to the U.G.C. (India) for financial assistance.     

Selective extraction of palladium(II) using hydrazone ligand: A novel fluorescent sensor

The acyclic tridentate blue luminescent ligand (λ_ex=300 nm, λ_em=415 nm) quinoline-2-carboxaldehyde 2-pyridylhydrazone, HL, 1, was recognized as a new fluorescent chemosensor for Pd²⁺. In alkaline methanol complete fluorescent quenching was observed in the presence of 2 equivalents of Pd²⁺ that was further reflected in the solid phase fluorescence microscopic study.Ligand formed 1:1 complexes with Ni²⁺, Cu²⁺, Zn²⁺, Pd²⁺ and 1:2 complexes with Co²⁺, Fe²⁺ as obtained from Job's plot of continuous variation. The binding constants of different metal complexes (Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Pd²⁺) were estimated by fluorescence titrations. The ligand can selectively extract significant amount of Pd²⁺ from the aqueous mixture of metal ions, and the extraction efficiency was increased from 80% to 95% with increase in the molar ratio of HL, 1, to Pd²⁺ from 1 to 3. No significant interference was observed up to 2-fold excess addition of Cu²⁺ and Zn²⁺ and 100-fold excess addition of Co²⁺, Fe²⁺ and Ni²⁺over the Pd²⁺ ion concentration (1.0×10⁻³ M).     

Theoretical investigations on the spin Hamiltonian parameters and local structures for the trigonal Ni2+ centers in CsMgX3 (X=Cl,Br, I)

The spin Hamiltonian parameters (zero-field splitting and the anisotropic g factors) and the local structures for the trigonal Ni²⁺ centers in CsMgX₃ (X=Cl, Br, I) are theoretically investigated from the perturbation formulas of these parameters for a 3d⁸ ion in trigonally distorted octahedra, by including the ligand s-orbital contributions. Based on the studies, the local impurity-ligand bond angles β related to the C ₃ axis in the Ni²⁺ centers are found to be about 2° larger than the corresponding angles, β_H, in the hosts, due to the size mismatching substitution of Mg²⁺ by Ni²⁺. The theoretical results based on the inclusion of the ligand s-orbital contributions show an improvement when compared with those in the absence of the above contributions, especially for the ligand I^?.     

Removal of heavy metals from aqueous solutions using Fe3O4, ZnO, and CuO nanoparticles

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions with novel nanoparticle sorbents (Fe₃O₄, ZnO, and CuO) using a range of experimental approaches, including, pH, competing ions, sorbent masses, contact time, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The images showed that Fe₃O₄, ZnO, and CuO particles had mean diameters of about 50?nm (spheroid), 25?nm (rod shape), and 75?nm (spheroid), respectively. Tests were performed under batch conditions to determine the adsorption rate and uptake at equilibrium from single and multiple component solutions. The maximum uptake values (sum of four metals) in multiple component solutions were 360.6, 114.5, and 73.0?mg?g^?1, for ZnO, CuO, and Fe₃O₄, respectively. Based on the average metal removal by the three nanoparticles, the following order was determined for single component solutions: Cd²⁺?>?Pb²⁺?>?Cu²⁺?>?Ni²⁺, while the following order was determined in multiple component solutions: Pb²⁺?>?Cu²⁺?>?Cd²⁺?>?Ni²⁺. Sorption equilibrium isotherms could be described using the Freundlich model in some cases, whereas other isotherms did not follow this model. Furthermore, a pseudo-second order kinetic model was found to correctly describe the experimental data for all nanoparticles. Scanning electron microscopy, energy dispersive X-ray before and after metal sorption, and soil solution saturation indices showed that the main mechanism of sorption for Cd²⁺ and Pb²⁺ was adsorption, whereas both Cu²⁺ and Ni²⁺ sorption were due to adsorption and precipitation. These nanoparticles have potential for use as efficient sorbents for the removal of heavy metals from aqueous solutions and ZnO nanoparticles were identified as the most promising sorbent due to their high metal uptake.     

A Pyrene-based Highly Selective Turn-on Fluorescent Sensor for Copper(II) Ion and its Application in Live Cell Imaging

A new pyrene derivative (chemosensor 1) containing a picolinohydrazide moiety exhibits high selectivity for Cu²⁺ ion detection in mixed aqueous media (CH₃OH:H₂O = 7:3). Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence for the system. The apparent association constant (K _a) of Cu²⁺ binding in chemosensor 1 was found to be 2.75*10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5–8. Moreover, by means of fluorescence microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for detecting Cu²⁺ in living cells.     

A vibronic-structure analysis of optical spectra in ZnO:Ni3+ crystals by localized-vibration simulation

A theoretical study is reported of the vibrations associated with a Ni³⁺ impurity charged with respect to the ZnO lattice. The calculations were made by a recursive method in terms of the shell model for vibrations with different symmetries. The vibronic structure observed in the spectra of d-d intracenter transitions in the Ni³⁺ impurity has been interpreted using model calculations. Fiz. Tverd. Tela (St. Petersburg) 41, 618–622 (April 1999)     

Thermodynamics of substituted coumarin VII: Potentiometric and spectrophotometric studies of 1-acetyl-2-(coumarin-iminecarboxamide-3-yl) hydrazine transition metal complexes

The dissociation constant of l-acetyl-2-(coumariniminecarboxamide-3-yl) hydrazine (ACCH) has been determined potentiometrically in 0.1 M KC1 and 40% (v/v) ethanol-water mixture. The stepwise stability constants of the formed complexes of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and UO₂ ²⁺ with ACCH have been determined. The stability constants were found to UO₂ ²⁺ > Cu²⁺> Zn²⁺ > Ni²⁺ < CO²⁺ < Mn²⁺. The effect of temperature on the dissociation of ACCH and the stability of its formed complexes were studied. The corresponding thermodynamic functions were also determined and discussed. The spectral data of ACCH were investigated in pure organic solvents as well as in Britton Robinson buffer solutions of varying pH values. The dissociation constant pK^H ₁ of ACCH and the overall stability constants logβ of their complexes were determined in 20% (v/v) ethanol-water mixture at 298K.     

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Co²⁺) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺ ions.     

Characteristics of the structural properties and the electric conductivity in LaSrAl1−x NixO4 ceramics caused by the Jahn-Teller effect

In studying LaSrAl_1−x Ni_xO₄ ceramics, anomalies are detected in the concentration dependences of the lattice parameter c, the electrical resistance, and the sign change of the Hall constant at x≈0.6. It is shown that the collection of observed phenomena can be interpreted as a manifestation of the Jahn-Teller nature of low-spin Ni³⁺ centers. Fiz. Tverd. Tela (St. Petersburg) 41, 418–422 (March 1999)     

Spectral and scintillation characteristics of compound x-ray detectors based on calcium iodide crystals

The results of an investigation of the spectral and scintillation properties of pure and Tl⁺, Eu²⁺, Fe²⁺, Co²⁺, and Ni²⁺ activated calcium iodide crystals as well as the results of measurements of the scintillation characteristics of compound x-ray detectors based on calcium iodide crystals are reported. It is shown that paired CaI₂ and CaI₂:Tl crystals can be used to fabricate compound detectors with different fluorescence times. On account of their high light output and good energy resolution CaI₂ and CaI₂:Eu crystals are suitable for compound detectors with different technical light output. CaI₂ or CaI₂:Eu scintillators together with scintillators based on calcium iodide with iron-group luminescence quenching impurity (Fe²⁺, Co²⁺, and Ni²⁺) can be used to obtain compound detectors with different physical light output. Zh. Tekh. Fiz. 68, 71–73 (September 1998)     

Theoretical study of EPR spectra and local structure for (NiO6) cluster in LiNbO3:Ni and Al2O3:Ni systems

For a d⁸ configuration ion, the 45×45 complete energy matrix, which contains the electron-electron repulsion interaction, the ligand-field interaction, the spin-orbit coupling interaction as well as the Zeeman interaction, has been established. By diagonalizing the complete energy matrix, the local lattice structure, EPR parameters (D, g_//, g_⊥) and optical absorption spectra for Ni²⁺ ions doped in LiNbO₃ and Al₂O₃ have been investigated. The local structure distortion parameters ΔR, Δθ₁ and Δθ₂ are determined for LiNbO₃:Ni²⁺ and Al₂O₃:Ni²⁺ systems, simultaneously. These results show that local structure of (NiO₆)¹⁰⁻ cluster exhibits an elongation distortion in both LiNbO₃:Ni²⁺ and Al₂O₃:Ni²⁺ systems, in spite of the different reasons of the elongation in both systems. In addition, we have found that the orbit reduction effect is very important to understand the anisotropic g-factors for Ni²⁺ ions doped in LiNbO₃ and Al₂O₃ crystals.