TSL and EPR studies of SrBPO5 doped with CeO2 and co-doped with CeO2 and Sm2O3

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO₅ samples doped with CeO₂ and co-doped with CeO₂ and Sm₂O₃. On gamma-irradiation at room temperature, BO₃ ^2–, O₂ ^– and O^– radicals were produced. It was seen that the O^– radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O^– radical ions results in transfer of recombination energy to the impurity centre Ce³⁺ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce³⁺ to Sm³⁺ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.     

TSL and EPR studies of SrBPO5 doped with CeO2and co-doped with CeO2 and Sm2O3

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO₅ samples doped with CeO₂ and co-doped with CeO₂ and Sm₂O₃. On gamma-irradiation at room temperature, BO₃ ^2–, O₂ ^– and O^– radicals were produced. It was seen that the O^– radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O^– radical ions results in transfer of recombination energy to the impurity centre Ce³⁺ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce³⁺ to Sm³⁺ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.     

Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped calcium phosphate

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies on uranium doped calcium phosphate yielded mechanistic information on the observed glow peaks at 365, 410 and 450 K. TSL spectral studies of the glow peaks showed that UO₂ ²⁺ acts as the luminescent center. Electron paramagnetic resonance studies on gamma-irradiated samples revealed that the predominant radiation induced centers are H⁰, PO₄ ^2-, PO₃ ^2- and O^- ion. Studies on the temperature dependence studies of the EPR spectra of samples annealed to different temperatures indicate the role of H⁰ and PO₄ ^2- ions in the main glow peak at 410 K.     

On the mechanism of racemisation of dichlorobis(ethylenediamine)-metal chlorides [metal = cobalt(III) or chromium(III)] in the solid state

Summary In the solid state l-cis-[M(en)₂Cl₂]Cl [M=cobalt(III) or chromium(III)] undergoes thermal racemisation smoothly at 158 °C without anycis-trans interconversion. The values of k_rac, H and S are 6 × 10^–6s^–1, 218 kJM^–1 and 156.1 JK^–1M^–1 for the cobalt(III) complex and 3.5 × 10^–5s^–1, 229.7 kJM^–1 and 197.9 JK^–1M^–1 for the chromium(III) complex, respectively. The results are only in accord with a rhombic twist mechanism of the type originally proposed by Ray and Dutt for [M(AA)₃] complexes.     

The quenching of vibrationally excited N 2 + ions by various neutrals

Using a selected ion flow tube, the quenching of the vibrational excitation of N ₂ ⁺ (X, v0) by Ne, N₂, O₂, NO, and CO₂ was investigated, and the following thermal quenching rate coefficients, k_q, were obtained respectively (all in units of 10^–10 cm³ sec^–1): 0.045, 5, 1.2, 0.3, 1. For the charge transfer of N ₂ ⁺ with O₂, NO, and CO₂, the respective rate coefficients (in units of 10^–10 cm³ sec^–1) 0.5, 3, and 7 were obtained independently of whether N ₂ ⁺ (X) was vibrationally excited or not.     

Study of SO2 adsorption on titanium dioxide by IR spectroscopy and thermal desorption

Conclusions At least two different forms of chemisorbed SO₂ have been identified on the surface of anatase. The weakly bound SO₂ (a low-temperature peak with T_max=405–445 K, H_ads =85.7 kJ/ mole) is characterized by IR bands at 1330 and 1141 cm^– and is stabilized on coordinatively-unsaturated titanium ions. The strongly bound SO₂ (high-temperature peak with T_max=550–615 K) has a band at 1070 cm^–1. The thermal stability of SO₂ chemisorbed on TiO₂ is lower than on -Al₂O₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 503–505, March, 1989.     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.     

High-temperature transport and electrochemical properties of YBaCo4O7+δ

The total conductivity of oxygen-hyperstoichiometric YBaCo₄O₇₊ is predominantly p-type electronic at oxygen partial pressures from 5×10⁴ Pa down to the phase decomposition limit, 10^–11–10^–4 Pa at 973–1223 K. The ion transference numbers, determined by the oxygen permeation and faradaic efficiency measurements at 1073–1223 K, vary in the range 3×10^–5–2×10^–4 and increase with temperature. The oxygen permeability of YBaCo₄O₇₊ ceramics, with overall level similar to that of K₂NiF₄-type cuprates, is mainly limited by the bulk ionic conduction. Heating above 1050–1100 K and redox processes under oxidizing conditions lead to a first-order transition accompanied with extensive oxygen losses from the lattice, resulting in decreasing total oxygen content from 8.5 down to approximately seven atoms per unit formula. Except for the variations associated with this transition, the electron–hole conductivity and Seebeck coefficient are essentially p(O₂)-independent within the phase stability limits. The use of different synthesis methods, namely the standard ceramic technique and the glycine–nitrate process, has no significant effect on the properties of YBaCo₄O₇₊ ceramics. The thermal expansion coefficients averaged at 600–1100 K in air are (7.3–7.6)×10^–6 K^–1. Porous YBaCo₄O₇-based cathodes show a very high electrochemical activity in contact with LaGaO₃-based solid electrolyte at 873–1073 K.     

Ascorbate-induced oxidation of formate by peroxodisulfate: product yields,kinetics and mechanism

The slow reaction between peroxodisulfate and formate is significantly accelerated by ascorbate at room temperature. The products of this induced oxidation, CO₂ and oxalate (C₂O^2– ₄), were analyzed by several methods and the kinetics of this reaction were measured. The overall mechanism involves free radical species. Ascorbate reacts with peroxodisulfate to initiate production of the sulfate radical ion (SO^– ₄), which reacts with formate to produce carbon dioxide radical ion (CO^– ₂) and sulfate. The carbon dioxide radical reacts with peroxodisulfate to form CO₂ or self-combines to form oxalate. Competition occurring between these two processes determines the overall fate of the carbon dioxide radical species. As pH decreases, protonation of the carbon dioxide radical ion tends to favor production of CO₂.     

Reduction of Eu3 + to Eu2 + in Al-Codoped Silica Glasses Fabricated by the Sol-Gel Technique and CO2-Laser Processing

The spectroscopic properties of europium in aluminium codoped silica glasses produced by the sol-gel technique have been studied with respect to the dopant concentrations and the thermal processing applied to the samples. After thermal annealing at temperatures up to 950_°C the bright red fluorescence around 613 nm characteristic for the trivalent europium ions (Eu^{3 +}) has been observed. The lifetime was measured to be 0.1–2.4 ms depending on dopant concentrations and thermal treatment. Subsequent CO₂-laser processing in air (short time remelting) gave rise to a bright blue fluorescence consisting of two broad bands, lying around 450 and 490 nm, with their peak position depending on the ratio between the aluminium and europium concentrations. The fluorescence lifetimes were found to be shorter than 1 s. This blue fluorescence is attributed to the divalent europium ion (Eu^{2 +}), leading to the conclusion that the CO₂-laser processing of europium doped alumina-silica glasses resulted in the reduction of the trivalent to the divalent europium ion. Laser processing could therefore be a valid alternative to conventional thermal annealing for the generation of Eu^{2 +} in alumina-silica glasses.     

An open-shell INDO study of models for the stabilized O− ion in γ-irradiated alkaline ices

Structural models for stabilized O^– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O^– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH^– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O^– models. The hydrated O^– model is closely similar to the hydrated anions in KF · 4H₂O, NaOH · 4H₂O, and NaOH · 7H₂O. A second model is developed, involving H₃O⁺ along with H₂O, in the O^– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry.     

Radiation effects on thermal decomposition of ammonium perchlorate

Thermal decomposition of -irradiated (dose: 0–3.6 MGy) ammonium perchlorate was followed. The dynamic heating (range: 100–220 °C) and IR spectral measurements were carried out simultaneously. Temperature and dose brought a lowering in peak intensity of NH ₄ ⁺ and C10 ₄ ^– ions. Radiolytic products C10₃ and NH₃ are considered to initiate the decomposition process.     

ESR study of electron interaction in a Tc/Al2O3 system

An investigation was made into the nature of paramagnetic centers in a Tc/Al₂O₃ system under varying conditions as to heat treatment and technetium content, and in O₂ and CO adsorption environments. It was found that in the case of reduction at 573 K Tc²⁺ ions and, conceivably, other ionic forms developed and stabilized on the carrier surface. After reduction at 973 K two types of electron center appeared, whose concentration increased as reduction was prolonged. Signals were observed in the low fields (3–20 mT) of the ESR spectra having g₁ 13.5 and g₂>30, which could be assigned to free charge carriers in a cluster of metal atoms or ions. Adsorption of O₂ at 300 K caused O ₂ ^– ion radicals to form on the surface of the reduced Tc/Al₂O₃ samples, both electron centers and technetium ions constituting the electron donors. In the case of CO adsorption paramagnetic (CO) ₂ ^– particles appeared on the Tc/Al₂O₃ samples after prolonged exposure. On reaction with O₂ two types of O ₂ ^– ion-radical with differing thermal stability were formed.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1972–1978, September, 1992.     

Photosensitivity of paramagnetic centers in radiolyzed solid hydrogen cyanide

The photolysis of solid hydrogen cyanide and the effects of UV light on⁶⁰Co--irradiated HCN at 77 K were studied using an ESR technique. As in the case of radiolysis, the HZ₂C=N radical formed due to sticking of the H atom to the triple bond of the HCN molecule is the main radical product of low-temperature HCN photolysis. The C=N^– radicals are accumulated at 77 K in insignificant amounts (3 %). It was established that radical and ionic products stabilized in y-irradiated HCN possess photochromism and under the action of UV light enter photochemical reactions leading to their decomposition. Upon photobleaching, the concentration of H₂C=N^– radicals first increases two- to threefold because of the decomposition of H₂C=N^– ions and then decreases. The presence of radicals and ions formed upon the low-temperature radiolysis of HCN broadens the optical absorption band of the system, and the boundary of the action spectrum shifts from 280 nm (for nonirradiated HCN) to the visible region at 400–440 nm.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 859–863, April, 1996.     

Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

Infrared spectral analysis during the thermal decomposition of pure and irradiated crystalline NH4ClO4

Variable temperature /303–553 K/ IR spectroscopic studies are made during thermal decomposition of pure and -treated ammonium perchlorate /AP/. Decomposition is enhanced by radiation or in the presence of an additive /Gd₂O₃/. Intensity of the stretching /1100 cm^–1/ and bending /625 cm^–1/ frequencies of ClO ₄ ^– decrease on heating the KBr matrix even below 360 K. Above this temperature, a broad band develops over 480–510 cm^–1 in the pure and -treated AP which is attributed to ClO ₃ ^– /₄/.     

The effect of mechanical activation on the thermal decomposition of chalcopyrite

Experimental results on the influence of preliminary mechanical activation on the thermal decomposition of chalcopyrite are presented and discussed. The following experimental facts were found:

Accumulation of host—guest ion complexes with different counterions at the water—supercritical CO2 interface: a molecular dynamics study

The behavior of ion complexes at the water—supercritical carbon dioxide interface was considered by molecular dynamics simulations. The following complexes were studied: Cs⁺calix[4]crown-6, K⁺222 cryptate with chloride or dicarbollide (CCD^–) counterions, the Sr²⁺18C6 complex with the picrate (Pic^–) or perfluorooctanoate (PFO^–) counterions, and the Cl^–Tet ⁴⁺ complex with chloride counterions (Tet ⁴⁺ is a tetrahedral tetraammonium cation). The simulations demonstrate the analogy between aqueous interfaces with organic immiscible liquids and the CO₂ phase. Water and supercritical CO₂ are poorly miscible and form an interface. Most of the complexes are accumulated at the interface, instead of diffusing into the organic phase in which they should be more soluble. In addition, marked counterion effects are observed. The CCD^–, Pic^–, and PFO^– anions are surface active and are concentrated at the interface, but show different relationships with the complexes. The formation of ion pairs is precluded by the very hydrophobic CCD^– anions, which promote the extraction of cryptates as separated ion pairs to the CO₂ phase. Conversely, the extraction of the Sr²⁺ ions with 18C6 proceeds via a co-complexation mechanism, including the formation of the Sr18C6(PFO)₂, complex having a CO₂ affinity. The mechanism of assisted ion transfer to the CO₂ phase is discussed.     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.