Investigation of structural transport and magnetic properties of the system Li0.25Cu0.5Fe2.25- x Al x O4

Experimental data on X-ray electrical conductivity, thermoelectric coefficient, magnetic hysteresis and infrared absorption spectra of the system Li_0.25Cu_0.5Fe_2.25–x Al _x O₄ are presented. All the compounds, 0x2.25, showed cubic symmetry. Lattice constant values progressively decreased on increasing the Al³⁺ content. X-ray intensity calculations, magnetic hysteresis and infrared spectroscopy studies indicated the presence of Li⁺, Al³⁺ and Fe³⁺ at tetrahedral and octahedral sites, while Cu²⁺ is present only at the octahedral site. The activation energy and threshold frequency increased with increasing values ofx. The compounds withx1.50 aren-type, and those withx2.0 arep-type semiconductors. Magnetic hysteresis indicated that compounds withx1.50 are ferrimagnetic, and those withx2.0 are antiferrimagnetic. High coercive force,H _c, values and remanence ratios (J _R/J_S) showed that all the compounds exceptx2.0 exhibit single-domain behaviour. The probable ionic configuration for the system is suggested as Li _0.15 ⁺ Al _0.5 ³⁺ Fe _0.35 ³⁺ [Li _0.1 ⁺ Cu _0.5 ²⁺ Fe _0.4 ³⁺ Al³⁺]O ₄ ^2– .     

The effect of Ti4+ ions on some magnetic properties of lithium ferrite

Some magnetic properties of the spinel structure compound, Li_0.5+0.5x Ti _x Fe_2.5-1.5x O₄, wherex=0–0.5, have been studied by different methods. The initial permeability, _i, was measured as a function of temperature at a constant frequency of 10 kHz. A maximum value was observed for each composition indicating the Curie temperature,T _c , which decreases with increasing titanium concentration. The magnetization,M, and theB-H loop were measured atRT in the range of magnetizing field from 0–1200 Am^–1 and at constant fieldH=205 Am^–1, respectively. The relative permeability, _r, depends on the magnetizing field and composition. It was found from theB-H loop that the remanence induction,B _r, and the apparent loss energy,P _s, depend on the composition but the coercive force,H _c, is independent of composition.     

First Observation of the Cation-Cation Interaction of Actinides in Melts: NpO2 +-UO2 2+ System

Study of the absorption spectra of the NpO ₂ ⁺ ion in a CsCl melt containing 2 M UO ₂ ²⁺ , as well as in K₂UO₂Cl₄ and Cs₂UO₂Cl₄ melts (T = 700°C), allowed the first detection of the cation-cation interaction of actinides in melts. In all the molten salts studied, the cation-cation interaction of NpO ₂ ⁺ and UO ₂ ²⁺ is manifested most clearly (via appearance of an additional band) in the ³ H ₅ ³ H ₄ magnetic-dipole transition of the 5f ² configuration of the NpO₂ ⁺ ion (D _4h symmetry) near 1.6 m: Along with a sharp peak of unbound neptunyl(V) at 1660 nm, there is an equally sharp peak at 1633 nm belonging to the cation-cation complex. The intensity ratio for the peaks at 1633 and 1660 nm increases in the series of melts (UO ₂ ²⁺ in CsCl) < K₂UO₂Cl₄ < Cs₂UO₂Cl₄ by two orders of magnitude.     

Preparation of Li3-x H x TaO4 by means of hydrothermal synthesis and protolysis

Protolysis of lithium orthotantalates resulted in ion exchange of Li⁺ with H⁺ and Li_3–x H _x TaO₄ was produced. From the disordered NaCl-type form of Li₃TaO₄, Li_1.2H_1.8TaO₄ was produced by the ion exchange. The same compound was obtained directly from amorphous tantalum oxide and LiOH solution under hydrothermal conditions. Its lattice constant was calculated to bea=0.4270 (2) nm (standard deviation in brackets) in the cubic system. Substitution of Li⁺ with H⁺ in-Li₃TaO₄ resulted in formation of Li_1.1H_1.9TaO₄. Its lattice constants in the triclinic system are estimated to bea=0.892 (1),b=0.852 (2),c=0.944 (1) nm,=89.1 (1),=117.1 (1) and=87.1 (1)°. An expansion of thea-axis on the ion exchange and the composition imply that Li⁺ ions forming corrugated planes stacked along thea-axis in the ordered Nacl-type structure was replaced with H⁺.     

Complexation of polyethylene glycol with Sr<Superscript>2+</Superscript> and Ba<Superscript>2+</Superscript> cations in extracts containing chlorinated cobalt dicarbollide

The composition and structure of complexes that are formed in the system consisting of chlorinated cobalt dicarbollide (CCD), polyethylene glycol (PEG), and Sr²⁺ or Ba²⁺ in a polar diluent, dichloroethane or phenyl trifluoromethyl sulfone, were studied by IR and NMR spectroscopy. In extraction of Sr²⁺ and Ba²⁺ with solutions of [H₅O ₂ ⁺ PEG]CCD^–, the organic phase contains the ionic associates [M²⁺PEG]CCD ₂ ^– . The Sr²⁺ and Ba²⁺ complexes have similar composition and structure: The oxygen atoms of two OH groups and six COC groups of a PEG molecule fill the first coordination sphere of the metal ions. Also, no more than two water molecules can be coordinated in the second sphere, forming hydrogen bonds with the hydrogen atoms of two OH groups of PEG. The coordination of the OH groups of PEG with the Sr²⁺ and Ba²⁺ ions is preferable over the coordination of the COC groups, as follows from the fact that the extraction of Sr²⁺ and Ba²⁺ with CCD-PEG mixtures gets worse on replacement of the OH groups of PEG by other substituents. A considerable increase in the efficiency of Sr²⁺ and Ba²⁺ extraction with H-CCD solutions in the presence of PEG is due to the fact that all the H₂O molecules in the first coordination spheres of the M²⁺ ions are replaced by the COC and OH groups of PEG with the formation of a hydrophobic complex [M²⁺PEG](H₂O)₂.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 540–545.Original Russian Text Copyright © 2004 by Stoyanov, Smirnov, Babain, Antonov, Peterman, Herbst, Todd, Luther.     

Sintering of (alumina + titanium) powder mixtures and elaboration of the corresponding cermets

We considered the possible formation of a bond between a ceramic (Al₂O₃) and a metal (titanium). We first concluded that a direct bonding of these two materials would be very unsatisfactory. We managed to obtain good bonding through an (Al₂O₃ +xTi) cermet placed between the two initial materials. Diffusion tests with Al₂O₃/Ti or (Al₂O₃ +xTi)/Ti couples have shown the appearance of densified layers in the diffusion zone. The study of the influence of the titanium content in the cermet permitted values ofx to be determined which give an appropriate continuity (10 x 25 wt%) across the interface. Measurements by micro probe have shown that the mobility of the Al³⁺ ion has a predominant influence in the process leading to the bonding. The nature of the sintering atmosphere plays an important role in the sintering capacity of (Al₂O₃ +xTi) cermet as well as the densification of the samples.     

Electrical Conductivity of H2V12 – y W y O31 + δ · nH2O and H x V x W1 – x O3 · nH2O

The electrical conductivity of H₂V_{12 – y} W _y O_{31 +} · nH₂O (0 y 3) and H _x V _x W_{1 – x} O₃ · nH₂O (x = 0, 0.08, 0.17, 0.25, 0.33) prepared by the sol–gel method was measured between 293 and 473 K at a relative humidity of 12%. Partial substitution of tungsten for vanadium or V⁵⁺ and H⁺ for tungsten was found to reduce the conductivity of the phases studied. The only exception is the x = 0.33 phase. Below 373 K, the activation energy of conduction is 0.22–0.29 eV in the amorphous phases (0 y 3; x= 0.25, 0.33) and 0.06–0.11 eV in the crystalline phases (x = 0, 0.08, 0.17). The possible mechanisms of electrical transport are discussed.     

Electrical properties of Si4+ substituted copper ferrite

The electrical resistivity, , and Seebeck coefficient, , for the system Cu_1+xSi_xFe_2–2xO₄ (where x = 0.05, 0.1, 0.15, 0.2 and 0.3) have been studied as a function of temperature. Temperature variation of the resistivity exhibits two breaks. Each break is associated with a change in activation energy. The conduction process at low temperature is governed by the reaction Cu _A ¹⁺ + Cu _A ²⁺ Cu _A ²⁺ + Cu _A ¹⁺ . However, at higher temperature, it is due to intersite cation exchange and reoxidation such as Cu _A ²⁺ + Fe _B ³⁺ Cu _B ²⁺ + Fe _A ³⁺ . Measurement of the Seebeck coefficient, , from room temperature to 800 K reveals n-type conduction for the sample with x= 0.05, while the measurements for other samples show p-type conduction for lower temperatures and n-type conduction at higher temperatures. The activation energies in the paramagnetic region are found to be less than those in the ferrimagnetic region.     

Kinetics of Pu(IV) Reduction with Butanal Oxime

The reduction of Pu(IV) with butanal oxime in nitric acid solution in the presence of excess reductant follows the equation 4Pu^{4 +} + 2C₃H₇CHNOH + H₂O = 4Pu^{3 +} + 2C₃H₇CHO + N₂O + 4H⁺, and its rate is given by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²[C₃H₇CHNOH]/{[Pu(III)][H⁺]}. The rate constant is k = 3.65±0.14 min^{- 1} at 20.2°C and the solution ionic strength = 2. The activation energy is E = 88.8±10.3 kJ mol^{- 1}. The probable reaction mechanism is discussed.     

Electrospinning preparation and luminescence properties of one-dimensional SrWO4: Sm3+ nanofibers

One-dimensional Sm³⁺ doped SrWO₄ with or without different charge compensation approaches (co-doping Li⁺, Na⁺ and K⁺) nanofibers were prepared by electrospinning. The structure, morphology and luminescence properties of the obtained nanofiber phosphors were investigated. The X-ray diffraction, Fourier transformation infrared and thermogravimetric results show that the Sr_(1?x)WO₄: Sm _x ³⁺ samples crystallize at 700 °C. Scanning electron microscope results indicate that as prepared nanofibers before/after calcination present uniform fiberlike morphology. The luminescence results show that Sr_(1?x)WO₄: Sm _x ³⁺ phosphors can be excited efficiently by ultraviolet (UV) and near-UV light. The emission spectrum consists of three emission peaks at 561, 596 and 643 nm, corresponding to ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 transitions of Sm³⁺, respectively. The optimal doping concentration of Sm³⁺ in SrWO₄ is experimentally ascertained to be 4 mol%. The introduction of charge compensator R⁺ (R = Li, Na and K) can enhance the emission intensity of phosphors significantly. The co-doping of Li⁺ has the best compensation effect. The present investigation indicates that Sm³⁺ doped SrWO₄ is a promising orange phosphor for light-emitting diode based on UV chip technology.     

Electrical conductivity of polycrystalline lithium vanadium bronzes

Polycrystalline lithium vanadium bronzes, Li _x V₂O ₅ with different values of x have been prepared by both high temperature synthesis and room temperature chemical lithiation techniques. Electrical conductivity of the specimens initially increases with lithium concentration. The maximum conductivity is obtained in the phase for the high temperature prepared specimens and in Phase II for the room temperature prepared specimens. V⁴⁺ concentration of the specimens has been measured by a spectrophotometric technique and its variation has been correlated with the preparation condition and conductivity.     

Kinetics of Np(VI) Reduction with Butanal Oxime

Reduction of Np(VI) to Np(V) with butanal oxime in the presence of excess reductant is presumably described by the equation 4NpO₂ ²⁺ + 2C₃H₇CHNOH + H₂O = 4NpO₂ ⁺ + 2C₃H₇CHO + N₂O + 4H⁺, and the reaction rate, by the equation -d[Np(VI)]/dt = k[Np(VI)][C₃H₇CHNOH]/[H⁺], with k = 230±15 min^-1 at 25°C and the ionic strength of the solution = 2. This equation holds for solutions with different values of the ionic strength and HNO₃ concentration. The activation energy is 69.4±12.4 kJ mol^-1.     

Effects of temperature and magnetization on the maximum solubility of 3He in 4He

The laws x^m=x^m(T=0)(1+ _T T²) and x^m=x^m(B=0)(1+ _M B²), giving the effects of temperature and magnetization on the maximum solubility of ³He in ⁴He, are derived using the theory of normal Fermi systems. The parameters _T and _M are expressed in terms of measurable quantities, such as the specific heat and the magnetic susceptibility of the pure and dilute phases. Our relations are consistent with the experimental measurements of _T at SVP and predict a significant dependence of _T on pressure. Estimates of the parameter _M are given. The effects of temperature and magnetization on the osmotic pressure are also discussed.INFN sezione di Padova, gruppo collegato di Trento.     

The preparation,characterization and electrical properties of copper manganite spinels,CuxMn3−xO4, 0 ⩽x ⩽ 1

Single-phase copper manganite spinels Cu _x Mn_3–x O₄ with 0x1 were prepared by a careful thermal processing of copper-manganese co-precipitated hydroxide precursors. Powder X-ray diffraction (XRD) analysis of these spinels revealed the presence of a tetragonally distorted single spinel phase, with tetragonal distortionc/a > 1 which decreases with copper content. Thermogravimetric analysis (TGA) curves, run in an oxygen atmosphere for all the compositions studied, are characterized by a stability step up to 250 to 300° C, followed by a domain of oxidation between 300 and 900° C and finally a domain of reduction that restores the initial stoichiometry of the samples. The oxidation is observed to occur in two successive steps. The phenomenon appearing at the low temperature is due to the oxidation of Cu⁺ ions, while that at higher temperature corresponds to the oxidation of Mn²⁺ ions in tetrahedral sites. Further, electrical resistivity measurements confirm the presence of Cu⁺ ions on the tetrahedral sublattice of spinel. Correlation of the results obtained by XRD, TGA and electrical resistivity measurements permits one to infer the cation distribution, given by Cu _x ⁺ Mn _1–x ²⁺ [Mn _2–x ³⁺ Mn _x ⁴⁺ ] O ₄ ^2– .     

Soft chemistry synthesis of MxV2O5 + ε·nH2O (MCo, Ni, Cu, Zn) nanowires

Recently a simple method was used for preparing nanowires M_xV₂O_5 + ε·nH₂O (MMg, Mn). It consists of mixing a boiling solution of vanadium oxide with the corresponding metal nitrate. In the present paper, this method was explored for preparing other nanowires layered M_xV₂O_5 + ε·nH₂O compounds (MTi, Cr, Fe, Co, Ni, Cu, and Zn). The results obtained show that If the precipitates are formed immediately after mixing the two solutions, such in case of titanium, chromium and iron, the structure and particles shape of the products are different from the layered compound M_xV₂O_5 + ε·nH₂O. However, if the precipitates start to appear only after several minutes of stirring, such in case of cobalt, nickel, copper and zinc, the phases obtained are similar to layered nanowires M_xV₂O_5 + ε·nH₂O. The amount of the metal inserted “M” was found to be lower than 25 at.% in all as-prepared samples. Nickel containing sample shows the highest inserted amount.     

Electron paramagnetic resonance of Cu2+ and VO2+ ions in phosphate glasses

Electron spin resonance (ESR) spectra ofx(CuO · V₂O₅ (1 –x) (Na₂O · P₂O₅) andx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) glasses for 0 x 40 have been studied at the X-band and at 300 K. It is found that forx 5, both Cu²⁺ and VO²⁺ are present, mostly as isolated species. Forx 10, broad resonance lines atg = 2.1524 forx(CuO · V₂O₅) (1 –x) (Na₂O · P₂O₅) and atg = 2.1448 forx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) are observed which may be mainly due to dipole-dipole type interaction between transition metal (TM) ions. Spin Hamiltonian parameters of TM ions have been calculated. Optical spectra of the sodium phosphate glasses doped with single TM ions have also been studied. The theoretical optical basicity, A_th, of these doped glasses has been calculated. It is found that for VO²⁺ ionsg ,g and increase whileA ,P and g _|/g decrease with increase in A_th. However, no significant change is observed in the spin Hamiltonian parameters of Cu²⁺ with the change in A_th.     

EXAFS study of a hot-pressed α′-sialon ceramic containing erbium as the modifying cation

The general composition for an-sialon isM _x(Si, Al)₁₂(O, N)₁₆, (the value ofx lies between 0 and 2), where M is a modifying cation such as Li⁺, Ca²⁺, Y³⁺ or a number of the lanthanide cations (Ln³⁺). This paper reports extended X-ray absorption fine structure (EXAFS) spectroscopy measurements of a hot-pressed erbium containing-sialon, using the synchrotron radiation source at Daresbury, UK. This technique provides short-range structural information within this engineering ceramic. The results suggest that the erbium modifying cation shows a preference for being located in one particular site within the ceramic network.     

Proton conducting composites of heteropolyacid hydrates dispersed with salt hydrates

Proton conduction in the composites of heteropolyacid hydrates (Phosphotungstic acid : PTA·nH₂O and Phosphomolybdic acid : PMA·nH₂O) with salt hydrates like Aluminium sulphate and Ammonium paratungstate (APT) as dispersoids has been studied and compared with the composites PTA : Al₂O₃ and PMA : Al₂O₃. Thermal analysis, XRD and IR studies on acid and salt hydrates dispersed phase systems reveal the formation of composites. A significant increase in the ionic conductivity has been observed in the composites. It has been found that the conductivity of 0.5PTA + 0.5Al₂(SO₄)₃·16H₂O is 1.1 × 10^–2 S·cm^–1 and that of 0.55PMA + 0.45APT is 1.3 × 10^–3 S·cm^–1 at 65% R.H. The temperature and humidity dependence of bulk electrical conductivity of the composites is also reported.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.     

Electron spin resonance linewidths of Co2+ in magnesium oxide

Electron spin resonance linewidths of Co²⁺ in single-crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Co²⁺ concentration from 310 to 9900 ppm. In contrast to the behaviour expected from dipolar broadening, the experimental peak-to-peak linewidth for the octed hyperfine lines were about twelve to fifty times less than the calculated dipolar linewidths according to temperature and concentrations. The peak-to-peak linewidths as determined experimentally increase from 0.8 mT at 310 ppm Co²⁺ to 4.0 mT at 9900 ppm Co²⁺ at a polar angle _H= O° and at 20 K. Peak-to-peak linewidths independent of polar angle but strongly dependent on temperature and slightly dependent on concentrations were observed. The ratio of moments M ₄ ^1/4 /M ₂ ^1/2 derived from the experimental data lay between 1.35 to 1.44 and the lineshapes were markedly Lorentzian in the range of temperature measured. The data suggest that Co²⁺ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined, after exchange energy, over the whole concentration range examined and that the exchange energy whose values lay between 6 and 77 GHz, varied linearly with concentration.