Electron spin resonance and optical absorption spectra of Cu2+ ions in Na2SO4-ZnSO4 glasses

Electron spin resonance (ESR) and optical absorption spectra of Cu²⁺ ions in Na₂SO₄-ZnSO₄ glasses have been studied. The ESR spectra of Cu²⁺ ion-doped glasses exhibited a pronounced peak atg=2.07 and a shallow quadruplet atg=2.35, the latter arising from the hyperfine splitting of g. ESR spectra of Cu²⁺ ion-doped glasses were also studied by varying the concentration of Cu²⁺ions, temperature and composition of the glasses. The optical absorption spectra exhibited a broad absorption band in the near infrared region, which is attributed to²B_1g²B_2g transition. By correlating the ESR and optical absorption data, the bonding orbital coefficients ² and ₁ ² for Cu²⁺ ions have been evaluated.     

Study of the colouring process in copper ruby glasses by optical and EPR spectroscopy

The mechanism responsible for the development of the ruby colour in silica glasses containing copper have been investigated by means of optical and EPR spectroscopy. During the striking treatment, the evolution of the concentration of Cu⁺ and Sn²⁺ has been followed through their luminescence bands, whereas the Cu²⁺ concentration has been monitored by the EPR spectra. To account for the data, a model for the colouring which involves two simultaneous redox reactions: (i)2Cu⁺Cu²⁺+Cu⁰ (ii)2Cu²⁺+Sn²⁺2Cu⁺+Sn⁴⁺ has been proposed. According to it, the role of tin is to act as a redox buffer to regenerate Cu⁺, therefore favouring the coalescence of Cu₂O colloids.     

Interface reaction between oxide glasses and Fe-Al-Si magnetic alloy

The interface reactions between oxide glasses and magnetic alloy, Fe-Al-Si (so-called Sendust), were analysed. The oxide glasses used were SiO₂-PbO, SiO₂-Na₂O, SiO₂-Li₂O and B₂O₃-Na₂O binary glasses. It was observed that the lattice constant of the alloy decreases and the saturation magnetic-flux density of the alloy increases on reaction with the glasses. It was found that the aluminium atoms in the alloy diffuse to the interface and dissolve into the glass melt as Al³⁺ ions, leading to the iron-rich composition of the alloy. On the other hand, Pb²⁺, Na⁺ and H⁺ ions in the molten glasses were reduced at the interface. Metallic lead particles about 20 m in diameter were found to be dispersed in the SiO₂-PbO melt. Reduced sodium was thought to evaporate from the SiO₂-Na₂O melt, and H₂ gas bubbles were observed at the interface between B₂O₃-Na₂O melt and the alloy. These reactions were analysed based on the standard free energy diagrams of oxidation-reduction reaction, and expressed as 3Pb _glass ²⁺ +2Al_alloy 3Pb+2Al _glass ³⁺ 3Na _glass ⁺ +Al_alloy 3Na+Al _glass ³⁺ 6H _glass ⁺ +2Al_alloy 3H₂+2Al _glass ³⁺     

Spectrochemical studies on charge transfer bands due to d0, d5 and d10 ions in a sodium silicate glass

Titanium, vanadium and copper are normally present in glasses in their variable valency states but only Ti⁴⁺ (3d⁰), V⁵⁺ (3d⁰) and Cu⁺ (3d¹⁰) ions were found to exhibit charge transfer bands in glasses in the ultra-violet region of light. The molar extinction coefficients of these ions were calculated at their wavelength maxima in a 30Na₂O·70SiO₂ glass using Beer's-Bouger's equation and the intensities of their bands were found to lie of the order of around 10³ gm mol lit^–1cm^–1. The values of the molar extinction coefficients for these ions were compared with those of Ce⁴⁺ (5d⁰), Cr⁶⁺ (3d⁰) and Fe³⁺ (3d⁵) ions calculated earlier in 30Na₂O·70SiO₂ glass at their wavelength maxima in UV-region. The mechanism of electronic transition was suggested as L M, M L and M L M charge transfer available till date as a result of absorption of high energy UV-radiation extensively for d⁰, d⁵ and d¹⁰ ions respectively in glass depending upon the glass melting conditions. The low energy tail, of the UV-bands due to all these ions were found to obey Urbach's Rule in the present sodium silicate glass. The intensities of the charge transfer bands due to these ions are expected to depend upon their nature and symmetries, electronic configurations and wavelength of maximum absorption in the glass.     

Control of electrical conductivity with the admixture of chlorine in copper tellurite glasses

Copper tellurite glasses containing. CuCI₂ with composition 65TeO₂-(35–x)CuO-xCuCl₂ (mol%) with x=0, 1, 2, 3, 4, 5 were prepared by quenching the melt. An increase in density with the addition of CuCl₂ and with a corresponding decrease in molar volume, has been observed. The d.c. conductivity of copper tellurite glasses is found to be very sensitive to the reduced valency rationC=[Cu⁺]/[Cu_total] and depends on the relative concentrations of Cu⁺ (reduced valency state) and Cu²⁺ (higher valency state) ions. It is found that by adding cupric chloride to the melt when the glass is formed, the chlorine in the salt which acts as an oxidizing agent alters the ratio of the concentrations of Cu⁺ and Cu²⁺ ions in the glass and hence the conductivity. It is found that more than 2 mol% of cupric chloride reduces the conductivity very sharply due to the formation of chlorine clusters in the form of local TeCl₂₊ whereas less than 2 mol% of CuCl₂ leads to an increase in conductivity due to the Cu⁺Cu²⁺ transition which is negligibly affected by the chlorine due to the formation of TeCl₂ which is amorphous in nature. The increase and decrease of electrical conductivity of glasses containing less or more than 2 mol% CuCl₂ is also interpreted in terms of the electronic transitions between the orbitals of tellurium 3d electrons, their binding energies and peak widths on the basis of XPS (X-ray Photoelectron Spectroscopy) study, and it was found that the increase in bandwidth supports the idea of clustering of chlorine above 2 mol% CuCl₂ and causing a decrease in the conductivity. Overall the conductivity is found to be somewhat uncontrollable in these glasses because it is not simply dependent on the concentration of Cu²⁺ ions.     

Kinetics of Reactions of Np and Pu Ions with Hydrazine Derivatives: XVII. Reaction of Pu(VI) with Hydroxyethylhydrazine

Reduction of Pu(VI) to Pu(III) with hydroxyethylhydrazine (HOC₂H₄N₂H₃) in HNO₃ solutions involves the following consecutive steps²: Pu(VI) + HOC₂H₄N₂H₄ Pu(V) + ...; Pu(V) + HOC₂H₄N₂H₄ ⁺ Pu(IV) + ...; Pu(V) + Pu(III) 2Pu(IV); and Pu(IV) + HOC_2H4N₂H₄ ⁺ Pu(III) + .... The overall kinetic equations of these steps were suggested, and their rate constants and activation energies were determined. The mechanisms of the four reaction steps, consistent with the experimental kinetic data, are discussed.     

Effect of thermal cycling on as-quenched and aged nickel-rich Ni-Ti alloy

The effect of Ni₄Ti₃ precipitates on the structure and transformation sequences in Ni-49%Ti alloy has been investigated using internal friction, electrical resistivity and electron microscopy studies. It has been confirmed that in the alloy without precipitates the transformation occurs following the sequence B2 R M on cooling and M B2 on heating with easily distinguished peaks on the internal friction curves and typical behaviour of the electrical resistivity, while the presence of the precipitates brings about complicated internal friction curves indicating either the appearance of two types of martensite or the transformation sequence: B2 ® B2 + R B2 + M M.     

Magnetic Resonance Studies of Impurity-Helium Solids Containing Hydrogen and Deuterium Impurities

Impurity-Helium Solids (Im-He) produced by injecting a mixed beam of helium and impurity gases into superfluid ⁴He have been investigated by electron spin resonance (ESR) and nuclear magnetic resonance (NMR) techniques. NMR signals from deuterium molecules in a D₂-He solid have been studied. Only samples prepared from gaseous mixtures containing high concentrations of D₂ molecules gave observable signals. The ESR experiments were performed on H and/or D atomic impurities in Im-He solids containing H, D, H₂, and D₂ in various combinations. The exchange tunneling reactions D+H₂HD+H and D+HDD₂+H were used to generate high concentrations of H atoms (10¹⁷/cm³) in Im-He samples.     

Cu2+ ions in sodium fluoride-sodium borate glasses studied by EPR and optical absorption techniques

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu²⁺ ions in 80Na₂B₄O₇-(20 – x)NaF – xCuO (NFNB) glass system with 0 x 6 mol% have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in sodium fluoride-sodium borate (NFNB) glasses were present in octahedral sites with tetragonal distortion. The number of spins (N) participating in resonance was calculated as a function of temperature for NFNB glass sample containing 1 mol% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility () was calculated at various temperatures and the Curie constant was calculated from the 1/ – T graph. The optical absorption spectra of these samples show a broad absorption band centered at 13280 cm^–1 which is assigned to the ² B _1g ² B _2g transition of Cu²⁺ ions in distorted octahedral sites. The optical band gap energy (E _opt) and Urbach energy (E) are calculated from their ultraviolet edges. It is observed that as the copper ion concentration increases, E _opt decreases while E increases. This has been explained as due to the creation of additional localized states by CuO, which overlap and extend in the mobility gap of the matrix. By correlating the EPR and optical data, the molecular orbital coefficients have been evaluated.     

Electron spin resonance spectra of Gd3+ ions in K2SO4-ZnSO4 glasses

Electron spin resonance (ESR) spectra of Gd³⁺ ions doped in K₂SO₄-ZnSO₄ glasses have been studied on an X-band ESR spectrometer at different temperatures (–120 to 150 C). The ESR spectrum at room temperature exhibits three prominent features with effectiveg-values of 5.6, 2.83 and 2.02. The spectra are similar to the U spectra familiar in many oxide and fluoride glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. Remarkable changes have been observed in the spectrum with changes in the temperature, concentration and glass composition. The broadening of theg 2.02 line with increasing Gd³⁺ ion content indicates that the dipole-dipole interaction between the resonant centres increases with increase in Gd³⁺ ion content. A weak band at 36350cm^–1 is observed in the optical absorption spectrum of 0.5mol% Gd³⁺ in K₂SO₄-ZnSO₄ glass which has been assigned to the transition⁸S_7/2⁶P_7/2.     

Resonance Effect on the Tunneling Reaction: H+H2→H2+H in Solid Hydrogen

The tunneling abstraction reaction: H+H₂H₂+H in -irradiated solid hydrogen has been studied using electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) spectroscopy and gas-chromatography. The rate constant for the tunneling reaction in solid hydrogen was found to decrease with the increase in the concentration of ortho-H₂ molecules in solid hydrogen. We concluded that the decrease in the rate constant is due to the energy level mismatching between reactant species of H+H₂ trapped and product species of H₂+H trapped in the reverse induced by inhomogeneous intermolecular interactions between ortho-H² molecules in solid hydrogen. This result indicates that resonance effects play an important role in tunneling reactions in solids.     

ESR of Cu2+and Tl2+ in thallium borate glasses

The electron spin resonance (ESR) and optical absorption spectra of Cu²⁺ were measured in thallium borate glasses in order to investigate the effects of glass transition temperature,T _g, upon the responses of cupric ion in alkali borate glasses. The ESR of Tl²⁺ induced by-ray irradiation was also obtained. An abrupt increase in the covalency of in-plane Cu²⁺-O-bonding was observed in the Tl₂O system as well as in the Na₂O system in a similar B₂O₃ composition range althoughT _g for the Tl₂O glasses has little dependency on the composition compared with the Na₂O glasses. The trend in the variation of the S-character of the Tl²⁺ unpaired electron with composition agreed with that of the covalency of in-plane Cu²⁺-O-bonding. The structure of the anion group present in Tl₂O glasses was also examined by laser reman spectroscopy.     

Reaction mechanism for the formation of intermetallic compounds from layered Sm/Fe powder obtained by mechanical milling

Solid-state reactions in layered Sm/Fe powder particles with an overall composition of Sm₁₂Fe₈₈, obtained by ball milling, have been investigated by X-ray diffraction. During annealing at 500C, one reaction, Sm+2FeSmFe₂ was observed in the time-range studied. However, during annealing at 800C, five reactions were observed: Sm+2FeSmFe₂, Sm +3FeSmFe₃, 2Sm+17FeSm₂Fe₁₇, 2SmFe₂+13FeSm₂Fe₁₇, and 2SmFe₃ +11FeSm₂Fe₁₇. It is proposed that such reactions occur by a nucleation and growth process. Reactions of samarium with iron can be governed by nucleation; Sm/Fe interfaces possessing a higher free energy per unit area can play an important role in the nucleation. The observed results are discussed.     

Optical and esr spectra of titanium (III) in Na2O-B2O3 and Na2O-P2O5 glasses

The optical absorption and the esr spectra of titanium(III) in binary Na₂O-B₂O₃ and Na₂O-P₂O₅ glasses have been studied. Titanium(III) produces two optical absorption bands around 20 000 and 14 000 cm^–1 which are assigned to the²B_2g ²B_1g and²B_2g ²A_1g transitions respectively of Ti³⁺ in a tetragonally distorted octahedral environment. The absorption bands in phosphate glasses are narrower and absorption coefficients higher than those in borate glasses. The esr spectrum of titanium(III) in all the glasses consists of a broad asymmetric line withg 1.94 in borate glasses, andg 1.92 in phosphate glasses; no hyperfine structure has been observed.     

Reactive processing of nickel-aluminide intermetallic compounds

NiAl have been fabricated by reactive sintering compacts of ball-milled powder mixtures containing Ni and Al. The reaction mechanism, as well as phase and microstructural development, were investigated by analyzing compacts quenched from different temperatures during reactive hot compaction. It was found that the reaction process was strongly affected by pressure, heating rates, heat loss from the sample to the environment. The application of 50 MPa prior to the reaction resulted in the intermetallic-formation reaction initiating at a temperature (480°C) much lower than that (550°C) when no pressure was applied. At high heating rate (50°C/min), when the heat loss is small, the formation of NiAl occurs rapidly via combustion reaction. On the other hand, if the heat loss is significant as in slow heating rate (10°C/min), the reaction process is controlled by solid-state diffusion. The phase formation sequence for the slow solid-state reaction was determined to be: NiAl₃ Ni₂Al₃ NiAl NiAl (Al-rich) + Ni₃Al NiAl.     

Microstructure and properties of supersaturated ZA27 alloy during natural ageing

The decomposition of the supersaturated solid solution of ZA27 alloy at room temperature has been investigated by X-ray diffraction, TEM and mechanical properties testing. Based on the results obtained, both continuous precipitation and cellular reaction occur during the decomposition process. The continuous precipitation follows the sequence: ₁ + spherical GP zones ₂ + elliptical GP zones ₃ + R + . The cellular reaction can be written: + + . The properties of the alloy depend on the microstructure. After 1 month of ageing, a series of changes of microstructure have taken place. The properties of the alloy are: _b=500 MPa, =13%,H _v=148.     

Solid Rare Gas Isolated Ionic Exciplexes for Deep UV and VUV Lasers

Emissions of ionic alkalihalide exciplexes (AX) ⁺ due to the B ²X ² transitions of Cs ²⁺ F ^–, Cs ²⁺ Cl ^– and Rb ²⁺ F ^– are reported for CsF (196.5 nm), CsCl (220.1 nm) and RbF (136 nm) isolated in Ne and Ar matrices under e–beam excitation. The C ² A ² transition could be only observed in the condensed phase (solid Ne) at 227 nm (CsF) and at 249.2 nm (CsCl). A higher emission efficiency of the ionic excimers in the condensed phase compared to gas phase is obtained. Apparently, a strong quenching of the BX bands is observed at AX concentrations larger than 0.6%. These band lineshapes are explained and attributed to the transition from      

ESR study of CuO-doped cordierite

The reactivity of cordierite precursor with CuO powder was studied by means of X-ray diffraction measurements and electron spin resonance spectroscopy. Two concentrations of CuO were used: 10 and 20 mol %. An ESR signal was detected after heating the mixture of cordierite precursor-CuO at 500°C showing that CuO begins to dissolve with the cordierite precursor. The reactivity strongly increased between 700 and 800°C, in relation to the transition amorphous -cordierite. However, the crystallization of -cordierite prevented the dissolution. Cu²⁺ was located in the amorphous phase and characterized byg=2.35 andg=2.08.     

Chemical approach to the conduction mechanism in copper tellurite glasses containing lutetium oxide

Measurements of d.c. electrical conductivity were made on 65TeO₂-(35 -x)CuO-xLu₂O₃ (mol%) glasses with x=0, 1, 2, 3, 4. The experimental results show that whenx is changed from 1 to 2 mol%, the conductivity increases due to the additional electrons obtained by the oxidation of TeO₂ as well as due to the Cu⁺ Cu²⁺ transition under the effect of interelectronic repulsion in the 4f shell of the lutetium present in the glass. Whenx is increased to greater than 2 mol%, the conductivity decreases because hopping is inhibited due to the formation of oxygen bridge associates or because of the strong ligand repulsive field of lutetium indicating its non-reactivity in the glassy network. The conductivity has a distinct maximum atx=2.     

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.