[en] Compounds of the formula LiCo_1-yCr_yO₂ (0.0≤y≤0.20 and y=1.0) have been synthesized by high temperature solid-state reaction and were characterized by XRD and FT-IR. Hexagonal a and c lattice parameters increase with increasing y as expected from ionic size effects. Cyclic voltammograms reveal that the phase transformation occurring at x=0.5 in Li_1-x(Co_1-yCr_y)O₂ is suppressed for y=0.05 and 0.10. Low-current (0.01 C; 1 C=140 mA g^-1) galvanostatic charging curves show that the deintercalation voltage for y=0.05 and 0.10 decrease for a given x as compared to LiCoO₂. Galvanostatic charge-discharge cycling of the Li(Co_1-yCr_y)O₂ cathodes at 0.14 C and 2.7-4.3 V (vs. Li) show that increasing amount of chromium content in the LiCoO₂ lattice drastically reduces the amount of Li that can be reversibly cycled. Ex-situ XRD of the cycled cathodes show that slight cation-mixing occurs in the layered structure for y=0.05 and 0.10 and could be the reason for their poor electrochemical performance. Reversible Li intercalation/deintercalation is not possible in LiCrO₂ in the voltage range 2.7-4.3 V

[en] Layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ was prepared by mixed hydroxide method and characterised by means of X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and charge-discharge cycling. The hexagonal lattice parameters obtained for the compound are: a=2.864 and c=14.233 Angst. XPS studies show that the predominant oxidation states of Ni, Co and Mn in the compound are 2+, 3+ and 4+, respectively with small content of Ni³⁺ and Mn³⁺ ions. Initial discharge capacity of 160 mAh/g was obtained in the range 2.5-4.4 V and at a specific current of 30 mA/g of which 143 mAh/g was retained at the end of 40 charge-discharge cycles. At lower current (10 mA/g) and in the voltage window 2.5-4.7 V, discharge capacity of 215 mAh/g is obtainable. From the voltage profile and cyclic voltammetry, the redox processes occurring at ∼3.8 and ∼4.6 V are assigned to the Ni^2+/4+ and Co^3+/4+ couples, respectively

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[en] Layered Li(Ni_1/2Mn_1/2)O₂ was prepared by the solution and mixed hydroxide methods, characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and studied by cyclic voltammetry (CV) and charge discharge cycling in CC and CCCV modes at room temperature (r.t.) and at 50 deg. C. The XPS studies show about 8% of Ni³⁺ and Mn³⁺ ions are present in Li(Ni²⁺_1/2Mn_1/2⁴⁺)O₂ due to valency-degeneracy. The compound prepared at 950 deg. C, 12 h, solution method gives a second cycle discharge capacity of 150 mA h g^-1 (2.5-4.4 V) at a specific current of 30 mA g^-1 and retains 137 mA h g^-1 at the end of 40 cycles. CV shows that the redox process at 3.7-4.0 V corresponds to Ni²⁺↔Ni⁴⁺ and clear indication of Mn^3+/4+ couple was noted at 4.2-4.5 V. The observed capacity-fading (2.5-4.4 V) is shown to be contributed by the polarisation at the end of charging. The cathodic capacity is stable up to 40 cycles in the voltage window, 2.5-4.2 V both at room temperature and 50 deg. C

[en] The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data

[en] Thermoluminescence glow curves of X-irradiated CsBr:Cu⁺ and CsCl:Cu⁺ are given and discussed. Cu⁺ centres are of a special category as they can trap electrons or holes forming Cu⁰ or Cu²⁺

[en] TL studies of CsBr, CsBr:Ag⁺, CsBr:Cu⁺, CsCl:Ag⁺, and CsCl:Cu⁺ crystals X-irradiated at liquid nitrogen temperature are made. Both, undoped and impurity-doped CsBr crystals exhibit two main glow peaks at 116 and 159 K. CsBr:Ag⁺ crystal exhibits three additional glow peaks (weak) at 133, 176, and 192 K. The main glow peaks in these crystals are attributed to the double migration of thermally activated Vsub(k) centers followed by a radiative recombination with trapped electrons. The formation and decay of these centers is supported by optical absorption studies. The formation of Ag⁰ and Cu⁰ and the enhancement of Vsub(k) centers is also discussed. Similar studies are made on CsCl:Ag⁺ and CsCl:Cu⁺ crystals. Two main glow peaks observed at 204 and 246 K in these crystals are attributed to Vsub(k) center as in the case of CsBr crystals. The glow peaks are analysed and the TL parameters are evaluated. (author)

[en] The electrical conductivity of AgI-Ag₂MoO₄ glass has been studied over wide composition, frequency and temperature range. The observed frequency dependent conductivity has been explained by using Jonscher's universal expression. The ionic conductivity and conductivity relaxation calculated from impedance and modulus spectra respectively were found to be thermally activated; and the activation energy obtained from both measurements are comparable. Systematic trends in the variation of the Kohlrausch parameter with composition, mobile ion concentration and activation energy have been observed and the results are compared with those obtained in other materials. 39 refs.; 9 figs.; 1 table

[en] The electron paramagnetic resonance spectra of VO²⁺ ions doped in ammonium and potassium oxalate monohydrate single crystals have been studied at room temperature and x-band frequency. In both the crystals it is found that vanadyl goes substitutionally to the ammonium or potassium positions. The angular variation of the EPR spectra has been studied in the three crystallographic planes and the orientation of the vanadyl molecule (V-O) in the lattice has been determined. All the spectra have been analysed by using the usual spin-Hamiltonian corresponding to rhombic symmetry and the spin-Hamiltonian parameters are presented. The optical spectra of vanadyl ion in both the oxalates are essentially similar, with bands observed at around 735, 650 and 575 nm. By correlating the EPR and the optical absorption data the covalency rates of sigma bonding between the vanadium atom and the vanadyl oxygen have been estimated. (author)