Electrical conductivity and ESR of lithium borate glasses containing mixed transition metal oxides

Electron spin resonance, optical spectra and d.c. electrical conductivity of 2Li₂O · 3B₂O₃ glasses doped with V₂O₅ and CuO were investigated. Spin Hamiltonian parameters of transition metal (TM) ions have been determined. The theoretical optical basicity _th of these glasses has been calculated and related to the spin-Hamiltonian parameters of TM ions. The variation of electrical conductivity with composition has been explained.     

Electron spin resonance in phosphate glasses containing mixed transition metal ions

Phosphate glasses containing mixed Cu²⁺/Ni²⁺ and Cu²⁺/Co²⁺ oxides have been examined. A pronounced decrease in the optical absorption at 830 nm due to the Cu²⁺ ions is observed as the CuO in the glasses is gradually replaced by NiO or CoO and the decrease is accompanied by a pronounced decrease in the strength of the electron spin resonance (ESR) signal at 9.52 GHz. By combining the ESR and optical absorption data it is concluded that the decrease in concentration of Cu²⁺ ions in phosphate glasses may be due to an oxidation-reduction mechanism between two valency states of the two different transition metals, of the form Cu²⁺+Ni⁺Cu⁺+Ni²⁺ and Cu²⁺+Co⁺Cu⁺+Co²⁺.     

Optical and magnetic properties of transition metal oxides

The extremely strong coupling of conduction electrons with local spins in transition metal oxides leads to many intriguing electronic and optical properties, which are currently of great interest. Among these intriguing properties, the discovery of colossal magnetoresistance in manganese oxides has sparked a number of studies on the magnetic and electronic properties of these materials as well as the exploration of the relevant new materials phase.     

Infrared spectra,X-ray investigations and electrical conductivity of lithium borosilicate glasses containing transition metal oxides

The conductivities of lithium borosilicate glasses containing 2.5 mol % V₂O₅, MnO, Cr₂O₃, Fe₂O₃ and CoO were measured for untreated and heat-treated glasses (for 5 h at 480, 580 and 680°C). Both IR and X-ray diffraction techniques were used to investigate the microstructure of these glasses before and after heat-treatment. Lithium metasilicate and lithium metaborate were the main separated phases in addition to lithium disilicate in samples containing Fe₂O₃. The silicon ions are coordinated to four oxygens in tetrahedral coordination and some borons changed from triangular to tetrahedral.     

Study of mixed heavy metal fluoride bismuth borate glasses for optical applications

Journal of Materials Science: Materials in Electronics - To investigate the structural, optical and spectroscopic properties for possible applications in optical and shielding materials, the...     

Gamma rays interaction with bismuth borate glasses doped by transition metal ions

Ultraviolet, visible, and infrared spectroscopic measurements have been employed to investigate undoped binary bismuth borate glass (60 mol% Bi₂O₃, 40 mol% B₂O₃) and doped samples with 0.2% 3d transition metal oxides in order to obtain information about the role of all the constituents oxides including the dopants on the measured properties. The undoped sample shows strong extended UV-near visible absorption bands which are attributed to both trace iron impurities from raw materials used for glass preparation and Bi³⁺ ions. The TM-samples show the same strong UV-near visible absorption as the undoped sample beside characteristic visible bands because of TM ions. The prepared samples show obvious shielding behavior toward the effect of successive gamma irradiation especially in the visible region. The infrared absorption spectra of the prepared samples show characteristic bands related to the sharing of triangular and tetrahedral borate groups together with Bi–O groups. The IR spectra are slightly affected by gamma irradiation indicating the stability of network forming units while the modifier, OH and water bands show obvious changes in their intensities.     

Defects and electrical conduction in mixed lanthanum transition metal oxides

Lanthanum and transition metal mixed oxides form an interesting series of compounds with a general formula LaMO₃ (with M = Ti, V, Mn, Cr, Co, Ni and Fe). These compounds have been investigated by many workers as regards to their various physical parameters including the electrical conductivity. The new data reported in this paper refer to the Seebeck coefficient (S) in the temperature interval 300 to 1250 K. Electrical conductivity as a function of temperature has also been reported in the same temperature range and this is quite consistent with the values reported in the literature. Using these and other relevant data reported in the literature it has been concluded that native defects are mainly responsible for the electrical conduction in these solids. The nature of defect centres, charge carrier and their electrical transport mechanism is briefly discussed.     

Optical properties of oxide glasses containing transition metals: Case of titanium- and chromium-containing glasses

One of the major driving forces for the development of new glasses is the demand for high optical non-linearity with reduced cost and a higher damage resistance. Oxide glasses with large non-linear refractive index and non-linear absorption coefficient are promising materials for fiber telecommunication and for non-linear optical devices such as ultrafast optical switches, power limiters, real time holography, self-focusing, white-light continuum generation and photonic applications. To get insight into the optical absorption in amorphous materials, studies are still needed for revealing the nature of photoelectronic excitations in these materials by comparison with that in crystals which have been understood firmly based on band theory. Although the IR absorption loss in oxide glasses is larger than of fluorides, low light scattering loss is expected in these oxide glasses because they have lower glass transition temperature. In addition, small concentration of dopant such as alkaline metal and alkaline earth metal elements gives rise to the structural relaxation of the frozen-in density fluctuations even below glass transition temperature T_g, adding to the reduction of T_g as well. A review of the fundamentals and recent research advances in optical properties of oxide glasses containing chromium or titanium is presented.     

Interface reactions between glass melts containing transition metal oxides and ferrites

The interface reactions between SiO₂-PbO-MO melts (M = Fe, Mn, Zn and Ni) and Mn-Zn and Ni-Zn ferrites were studied using electron probe microanalysis and X-ray diffraction. Ni ions in the glass melt containing NiO were localized at the interface between the glass and Mn-Zn ferrite. The Ni-rich layer was also detected at the interface between NiO containing glass melt and Ni-Zn ferrite; the composition of this layer was thought to be close to NiFe₂O₄. Pb₈NiSi₆O₂₁ crystal was deposited as the product of the reaction with the glass melt and Mn-Zn ferrite at 700 °C. As compared with Mn-Zn ferrite, no reaction products were formed in Ni-Zn ferrite at various temperatures. The dissolution length of Mn-Zn ferrite in SPN5 glass melt was found to be smaller than for other melts, and it is concluded that the NiO-rich layer at the surface of the ferrite is chemically very durable to the glass melts.     

Elastic moduli of some mixed alkali borate glasses

Elastic moduli of mixed alkali borate glasses based on lithium and sodium oxides are calculated by measuring ultrasonic velocities and densities. For the purpose of measuring the velocity with high accuracy, the McSkimin criterion for determining the correct cyclic overlap between echoes is used. The structure of the system is discussed as a function of composition by considering the behaviour of elastic properties. Infrared studies have also been done which confirm the conclusions reached by the ultrasonic studies of the given system.     

Synthesis and X-ray structural investigation of undoped borate glasses

A series of undoped borate glasses: Li₂B₄O₇, LiKB₄O₇, LiB₃O₅, SrB₄O₇, and LiCaBO₃ of high optical quality and chemical purity were obtained from the corresponding polycrystalline compounds using standard glass synthesis under technological conditions developed by the authors. The glasses were obtained by rapid cooling of molten crystalline material, which was heated to 100 K above the melting point to prevent crystallization and to exceed the glass transition point. The X-ray diffraction intensity profiles of the investigated glasses were typical of glassy compounds. The most typical intensity profile, consisting of almost symmetrical peaks, was observed in the case of Li₂B₄O₇ and LiB₃O₅. Substitution and partial substitution of Li atoms by Sr and Ca atoms was accompanied by significant changes in the intensity profiles of the investigated glasses. Pair correlation functions and structural parameters (average interatomic distances and coordination number to oxygen) of the investigated glasses were evaluated and analyzed. Structural peculiarities of the investigated borate glasses are discussed in comparison with structural data available for their crystalline analogs.     

Optical absorption of Nd, Sm and Dy in bismuth borate glasses with large radiative transition probabilities

This paper reports on the optical properties of Nd³⁺, Sm³⁺ and Dy³⁺ in bismuth borate glasses, with Bi₂O₃ content varying from 30 to 60 mol%. The variation of the optical properties with composition plays a dominant role in determining a good laser host material. The variation of the Judd–Ofelt intensity parameters Ω_t (t=2,4,6) and the radiative transition probabilities and the hypersensitive band positions, with composition, have been discussed in detail. The changes in position and intensity parameters of the transitions in the optical absorption spectra are correlated to the structural changes in the host glass matrix. The variation of Ω₂ with Bi₂O₃ content has been attributed to changes in the asymmetry of the ligand field at the rare earth ion site and to the changes in their rare earth–oxygen (R–O) covalency, whereas the variation of Ω₆ strongly depends on nephlauxetic effect. The shift of the hypersensitive band shows that the covalency of the R–O bond increases with increase of Bi₂O₃ content, due to increased interaction between the rare earth ions and the non-bridging oxygens. The radiative transition probabilities of the rare earth ions are large in bismuth borate glasses, suggesting their suitability for laser applications.     

Molar volume and magnetic susceptibility of borate glasses containing iron

A glass system was prepared from reagent grade chemicals having the formula 58 mol % B₂O₃ - 22 mol % CaO - (20 - ) mol % Al₂O₃ - mol % Fe₂O₃, where has different values between 2 and 20 mol %.The molar volume () and magnetic susceptibility () of these glasses has been measured as a function of Fe₂O₃ content. The values of and were found to increase as the Fe₂O₃ content in the glass increases in the region between 2 and 8 mol % and in the region where the content is greater than 10 to 16 mol %, while a decrease was found for samples having an Fe₂O₃ content of 10 mol % and more than 16 mol %. These results could be explained by the change in coordination of iron from FeO₆ to FeO₄, and also the change of Fe³⁺ to Fe²⁺ and change of Fe²⁺ from six coordination to four coordination.     

Ultrasonic investigation and infrared absorption of some sodium borate glasses

Ultrasonic velocities and absorption measurements in sodium borate glasses containing Na₂O have been made using the pulse echo technique at 4, 5 and 6 MHz. Results showed an increase in velocity as the sodium oxide content (mol%) increased. The ultrasonic absorption results showed the presence of very high and well-defined peak which shifts its position to lower temperatures with increasing frequency. This suggests some sort of relaxation process and the activation energy of this process increased with increasing Na₂O concentration (mol%). The infrared absorption spectra of sodium borate glasses confirmed the results obtained by ultrasonic investigations.     

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.     

Porphyrin based hybrid borate glasses: Structure and photophysical investigation

Freebase tetra phenyl porphyrin (H₂TPP) and its derivatives in different concentration ranges (0.5–2.0 mg per 12 g of boric acid) were incorporated into borate glass matrix by melt quenching technique at 230 °C. The formed glasses were stable and in green colour. The optical absorption and emission properties are different from that observed in solutions. The absorption spectrum shows a two line pattern Soret band at 435–454 nm and Q-band at 665–701 nm. The emission spectrum shows strong S₂ → S₀ emission at 490–520 nm region and S₁ → S₀ emission at 725–810 nm. The time resolved fluorescence decay of S₁ → S₀ emission shows three exponential decay. For example, in the case of 2 mg of H₂THP doped glass the lifetimes were found to be τ₁ = 0.511 ns (26.7%), τ₂ = 10 ps (64.68%) and τ₃ = 3.965 ns (8.62%). These unusual photophysical properties were found to arise from different structural motifs of porphyrin in the glass. These structures were further modeled through reactions of porphyrin with BF₃O(C₂H₅) in solution and DFT calculations.