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.     

Magnetic and electrical properties of lithium borosilicate glasses containing nickel and iron oxides

Measurements of a.c. conductivity, dielectric constants, Mo¨ssbauer spectra and magnetic susceptibility were carried out on samples of composition: 20LiO₂, 31B₂O₅, 34SiO₂, 15 – x NiO, xFe₂O₃ where x = 2.5, 5, 7.5, 10 and 12.5 mol %. It was found that when x is changed from 2.5 to 10 mol % NiO, the conductivity decreases due to the increase of the bridging oxygen ions. When x is increased to greater than 10 mol % NiO, the conductivity increases because of the decrease of the ratio of Fe²⁺Fe³⁺ ions as confirmed from Mo¨ssbauer data. The conductivity has a distinct minimum at 10 mol % NiO. Distribution of relaxation processes was also studied, and two processes were adequate to describe the present experimental data.     

Magnetic susceptibility of lithium borosilicate glasses containing metal oxide

Lithium borosilicate glasses with different chromium, manganese and cobalt contents were prepared and heat treated at 480, 580 and 680° C for 5 h. The magnetic susceptibilities of untreated and heat-treated samples were measured. The magnetic susceptibility was found to increase as the Cr₂O₃, MnO or CoO content increased. The values for magnetic susceptibility were co-related to the relative proportion of valence states of transition elements. The magnetic susceptibilities were found to have random behaviour with heat-treatment temperatures. Samples containing Cr₂O₃ showed transformations from diamagnetic to paramagnetic behaviour with the increase in Cr₂O₃ content, which may be due to the change of chromium ions from the high valence to the low valence state.     

Infrared and Raman spectra of binary tellurite glasses containing boron and indium oxides

The constitution of glasses in the systems M₂O₃-TeO₂ (M = B and In) was investigated by Raman and infrared spectroscopy. From the relation between the M₂O₃ content and the intensity ratios of the deconvoluted Raman peaks I(720)/I(665) and I(780)/I(665), it was concluded that In₂O₃ behaves as a network modifier to yield TeO ₃ ^– units and that discrete BO₃ and BO₄ units construct a network of glasses containing boron oxide. A structural model for those glasses was derived which involves three-coordinated oxygen atoms and TeO₄ units of an intermediate configuration, O₃Te⁺ ...O^-.     

Optical and ESR investigation of borate glasses containing single and mixed transition metal oxides

The optical and electron spin resonance (ESR) spectra of barium borate glasses, containing the oxides of V, Fe and Cu separately and in mixed proportions, have been studied. The optical spectra of the single transition metal (TM) oxide glasses showed the usual features, while those for the mixed glasses showed single bands without showing individual features of the single TM oxide glasses. However, the linear plots of optical density against composition revealed the presence of two valence states for each TM element, and this was confirmed by ESR results as well. The ESR spectra of the mixed glasses showed a complicated interaction pattern for two different TM ions, in comparison with those of the glasses containing a single TM ion. For the Fe-V glasses, the progressively vanishing hyperfine structure of the VO²⁺ complex with increasing addition of iron oxide is discussed in terms of nuclear spin relaxation, cross-relaxation between two spin systems and spin diffusion within the vanadium spin system. The covalency of the VO²⁺ complex and the number of distorted Fe³⁺ ions were found to decrease with increasing addition of Fe₂O₃ replacing V₂O₅. Similar features were noted for the Cu-V glasses; the spectra of Cu-Fe glass also showed a strong interaction between two different TM ions. It has been suggested that all the possible four valence states (for a given mixed glass) from two different TM elements are present, and that pairing of two different TM ions from two dissimilar TM elements occurs, facilitating the formation of associates (e.g. V⁴⁺-O-Fe³⁺).     

X-ray and electrical conductivity studies on iron-aluminium mixed oxides

Co-precipitated iron-aluminium mixed oxide cataiysts containing 0 to 100 mol % alumina have been studied by X-ray diffraction and electrical conductivity measurements. Formation of solid solution has been observed. At lower concentrations, aluminium ions occupy the interstitial sites while at higher alumina contents, it forms a substitutional solid solution. Electrical conductivity of the specimens has been measured in air and nitrogen atmospheres in the temperature range room temperature to 400° C. The influence of moisture is found to be significant and it increases with increasing alumina content. A straight line relationship exists between log and 1/Tfor all the specimens. The activation energies for conduction in air and nitrogen are observed to be in the range 0.25 to 0.35 and 0.24 to 0.29 eV, respectively. Electron holes are found to be responsible for electrical conduction in these materials.     

Structure,magnetic, and electrical studies on vanadium phosphate glasses containing different oxides

Glass system with molar composition (60% P₂O₅–30%V₂O₅–10%X) where X is Li₂O, Na₂O, K₂O, and BaO was prepared. The density and molar volume indicate that the density decreases while the molar volume increases with increasing ionic radius of doped oxides. IR studies reveal the coexistence of V⁴⁺ and V⁵⁺ ions (act as glass modifier and glass former, respectively). The observed paramagnetic behavior of samples indicates that V⁴⁺ > V⁵⁺ (the ratio V⁴⁺/V⁴⁺ + V⁵⁺ > 0.52 as obtained from chemical titration analysis). Mott’s model of conduction was applied to discuss DC electrical conduction mechanism. The prepared glass exhibits semiconducting behavior. However, Ba ion is the only ion which did not contribute to the ionic conduction. The conductivity increases with decreasing ionic radius of doped oxides due to high mobility due to their small size. The effect of hopping distance on the electrical conduction and magnetic properties were discussed. An attempt was done to determine the expected temperature of Ba ionic conduction and its ionic activation energy.     

Diffusion and electrical conductivity studies in some heterophase glasses containing bismuth

Self-diffusion coefficients of sodium in the temperature range 300 to 375° C have been measured for glasses in the system Na₂O-B₂O₃-Bi₂O₃-SiO₂, by using a radioactive tracer technique. All these glasses have a two-phase structure. The d.c. resistivities of these glasses were also measured over the temperature range 30 to 375° C. The correlation factors,f, of all the samples have been calculated by using the diffusion coefficients and d.c. resistivity values for temperatures above 300° C. The anomalously largef values in the case of Bi₂O₃-containing glasses are thought to be due to a distribution of sodium ions in the dispersed as well as the continuous phases in these systems.     

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.     

Insertion/extraction of lithium and sodium in transition metal oxides and chalcogenides

Lithium and sodium can be reversibly inserted into a variety of transition metal oxide and chalcogenide hosts at low temperatures. The reaction is essentially topochemical involving electron-transfer and accompanying diffusionless transformation of the anion array in many cases. Alkali metal insertion/extraction reactions provide new routes for the synthesis of novel solids exhibiting unusual structure and properties. It appears that while the structure of the insertion compound is determined by the host structure and the size of the alkali metal ion, the extent of insertion/extraction is decided by the redox characteristics and electronic conductivity of the host. Contribution No. 318 from the Solid State and Structural Chemistry Unit.     

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.     

X-ray photoelectron spectroscopy and Fourier transform-infrared studies of transition metal phosphate glasses

X-ray photoelectron spectroscopy and Fourier transform-infrared studies were carried out on phosphate glasses containing oxides of iron, cobalt, nickel, copper and zinc. The results suggest that the glasses containing iron and zinc may have structures in which both the phosphorus and the iron (or zinc) atoms are tetrahedrally coordinated by oxygen into three-dimensional structures which resemble the polymorphic forms of silica, whereas the glasses containing cobalt, nickel and copper may consist of polymeric chains of PO₄ tetrahedra bonded to adjacent tetrahedra via bridging oxygens. These polyphosphate chains are linked together by the interaction between the metal cation and the oxygens of the network former. In addition, the core level 2p shake-up satellites of the 3d-transition metal ions in these glasses were studied. The results support a suggestion that the satellites in the glass are most likely due to the electron transfer from ligand to metal 3d orbitals.     

X-ray,electrical conductivity,and infrared studies of oxide spinels containing cobalt,titanium and manganese

X-ray, electrical conductivity and infrared studies of the system Co_2–x Ti_1–x Mn_2x O₄ were carried out with a view to investigate the cation distribution. Compounds 0 x 0.6 showed cubic symmetry, compounds 0.8 x 1 are tetragonal. X-ray intensity calculation indicated the presence Of Co²⁺ and Mn³⁺ at both octahedral and tetrahedral sites. A plot of activation energy against composition shows a break where crystal symmetry changes. The electrical conductivity-temperature behaviour obeys the Raschhinrichsen law. The mobility of holes calculated from infrared and conductivity data is of the order Of 10^–9 cm² V^–1 sec^–1. X-ray intensity calculations and conductivity measurements suggest the ionic configuration of the system to be Co _1–x ²⁺ Mn _x ³⁺ [Co _2–2x ²⁺ Mn _x ³⁺ Ti _x ⁴⁺ ]O ₄ ^2– .     

Spectroscopic characterization of alkali borosilicate glasses containing iron ions

Structural properties of alkali borosilicate glasses containing iron ions were investigated using infrared, laser Raman and Mössbauer spectroscopy. Two types of glasses were prepared: SRL-type with the composition 18.5 wt% Na₂O, 10.0 wt% B₂O₃, 52.5 wt% SiO₂, 4.0 wt% Li₂O, 10 wt% TiO₂ and 5.0 wt% CaO, and sodium borosilicate glass with the composition 16.7 wt% Na₂O, 18.7 wt% B₂O₃ and 64.6 wt% SiO₂. Raman spectroscopy showed that orthosilicates are the dominant amorphous phase in the SRL-type of glass. Incorporation of iron in the SRL-type of glass induced polymerization of silicate units and -Si-O-Fe- copolymerization. It was concluded that different amorphous phases are simultaneously present in the SRL-type of glass containing iron ions. Interpretation of the Raman spectra is given. Incorporation of iron ions into the sodium borosilicate glass also affected the corresponding IR spectra. The valence state of iron and its coordination were determined by⁵⁷Fe Mössbauer spectroscopy.