Kinetics and Mechanism of Solid State Reactions in the Agl-TlI System

The kinetics of the solid state reactions AgI + TiI → AgTlI2 (I) Agl + AgTl2I3 → 2 AgTlI2 (II) AgTlI2 + Til → AgTl2I3 (III) are investigated with reactant pellets by the contact method. With the aid of inert marker experiments and transport number determinations it was possible to state that the governing mechanism is the cation counter-diffusion in all cases and that the rate determining step is the diffusion of Tl+. The experimental reaction rate constants agree reasonably with those calculated on the basis of the Wagner's thermodynamic theory

Kinetics of Formation of SrWO4 in the Solid State Reaction Between WO3 and SrCO3

The solid state reaction WO3 + SrCO3 → SrWO4 + CO2 was studied with the reactants in form both of separate pellets and of powder mixtures. As for pellets, by an application of Wagner's method it was possible to state that the governing process is the cation counterdiffusion involving W6+ and Sr2+. Thermogravimetric measurements in the temperature range 663° - 755 °C on equimolar powder mixtures and with SrCO3 in a specially prepared spherulitic form were interpreted using Dünwald- Wagner's equatio

On the Mechanism of CaWO4 Formation in the Solid State from CaO and WO3

The formation in the solid state of CaWO4 from CaO (single crystal) or Ca3WO6 and WO3 was investigated by the contact method between 800 and 1000 °C in air and in argon. The results obtained indicate that these reactions are governed by the diffusion of the W6+ and O2- ions. From the CaWO4 structure, along with the lattice disorder predominant in this compound (0 vacancies and 0 interstitials) and the values of ionic mobilities, it was possible to state that the oxygen diffusion, via V0 2·, represents the rate - determining step in the considered reaction

Structural, spectroscopic and magnetic investigation of the LiFe1-xMnxPO4 (x = 0 - 0.18) solid solution

Different solid state and sol-gel preparations of undoped and Mn substituted cathode material LiFePO4 are investigated. Li3PO4, Fe2P2O7 and Li4P2O7 are detected and quantified by XRPD only in solid state synthesis. In addition, micro-Raman spectra reveal low amount of different iron oxides clusters. EPR data, combined with the results of magnetization measurements, evidence signals from Fe3+ ions in maghemite nanoclusters, and in Li3Fe2(PO4)3. The sol–gel synthesis, showing the lowest amount of impurity phases, seems the most suitable to obtain a promising cathode material. The structural refinement gives new insights into the cation distribution of the Mn doped triphylite structure: (i) about 85% of Mn2+ ions substitutes Fe2+, the remaining 15% being located on the Li site, thus suggesting a structural disorder also confirmed by EPR and micro-Raman results; (ii) Mn ions on the Li site are responsible for the observed slight cell volume expansion

Cr and Ni doping of Li4Ti5O12: cation distribution and functional properties

Cr- and Ni-doped Li4Ti5O12 compound has been characterized through the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7Li nuclear magnetic resonance magic-angle spinning (NMR-MAS), micro-Raman, and magnetization measurements. The doping, occurring on the octahedral site of the cubic Li4Ti5O12 spinel lattice, strongly affects both the local and the average structural properties. The glassy character of the observed EPR signals suggests structural disorder in the stable Li4Ti5O12 matrix and the presence of clustering phenomena or nonhomogeneous distribution of the dopant ion, as also supported by 7Li NMR-MAS, micro-Raman, and magnetization results. The computation by numerical method of the complex EPR signal of the Cr-doped sample suggests that both CrTi and CrLi substitutions occur, giving rise to two distinct EPR components, corresponding to opposite axial distortion of the relative octahedral environments. On the basis of the compositional data, defect models involving oxygen or cation vacancies are proposed to explain the conductivity of the doped material

Pair distribution function analysis and Mössbauer study of defects in microwave-hydrothermal LiFePO 4

Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for high-energy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mössbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mössbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites. © 2012 The Royal Society of Chemistry

KLOE results in kaon physics and prospects for KLOE-2

The phi-factory DAPHNE offers a possibility to select pure kaon beams, charged and neutral ones. In particular, neutral kaons from phi->KS KL are produced in pairs and the detection of a KS (KL) tags the presence of a KL (KS). This allows to perform precise measurements of kaon properties by means of KLOE detector. Another advantage of a phi-factory consists in fact that the neutral kaon pairs are produced in a pure quantum state (J^(PC) = 1^(--)), which allowsto investigate CP and CPT symmetries via quantum interference effects, as well as the basic principles of quantum mechanics.A review of the most recent results of the KLOE experiment at DAPHNE using pure kaon beams or via quantum interferometry is presented together with prospects for kaon physics at KLOE-2.Comment: 5 pages, 4 figures, From Phi To Psi 2011 conference, to be published in Nuclear Physics B (Proceedings Supplements

Search for heavy neutral lepton production in K+ decays

A search for heavy neutral lepton production in K + decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to 10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4| 2 and |Uμ4| 2 for heavy neutral lepton mass in the ranges 170–448 MeV/c2 and 250–373 MeV/c2, respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2 and above 300 MeV/c2 for |Uμ4|2