Infrared spectra of the vitreous system Co3O4-P2O5 and their interpretation

The infrared absorption spectra of the vitreous Co₃O₄-P₂O₅ system have been measured in the frequency region 4000 to 200 cm^–1. Absorption bands and mode attributions have been fully discussed. Absorption frequencies and intensities are found to be strongly and systematically dependent on glass composition. On this basis it is found that this glass system can be divided into three distinct compositional regions. Similar three region behaviour is reported for the compositional dependence of density and molar volume of mixing of Co₃O₄-P₂O₅ glass. Quantitative justification for the band attributions has been attempted.On leave from the Physics Department, Faculty of Science, Monofia University, Shebeen El-Kome, Egypt.     

Infrared absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The Fourier transform infrared spectra of different compositions of evaporated V₂O₅/B₂O₃ thin films have been investigated. Most of the absorption bands corresponding to V₂O₅ and B₂O₃ films coincide with those reported by other authors. The short-range order in amorphous V₂O₅ films is found to be conserved. The absorption spectra indicate a boroxol ring structure for B₂O₃ films. In co-evaporated V₂O₅/B₂O₃ films the boron is observed to substitute in the V₂O₅ network such that the coordination number of vanadium ion remains unchanged. The presence of a number of bands corresponding to -OH groups indicates the hygroscopic character of the films.     

Optical absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The optical absorption spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been studied. For higher photon energies, the absorption is found to be due to a direct forbidden electronic transition process from the oxygen 2p band to the vanadium 3d band in a similar way to that observed in crystalline V₂O₅. The exponential behaviour of absorption edge for lower photon energies is attributed to the electronic transitions between the tailed-off d-d states corresponding to V⁴⁺ ions. For co-evaporated V₂O₅/B₂O₃ films the optical energy gap is observed to increase with the increase in V₂O₅ content of the composite films.     

Comparison between crystal field effects on the fluorescence spectra of crystalline SmP5O14 and vitreous (Sm2O3)0.248(P2 O5)0.752

To investigate how the local symmetry of the Sm³⁺ ion affects the fluorescence of a samarium metaphosphate glass of composition (Sm₂O₃)_0.248(P₂O₅)_0.752, the temperature and pressure dependences of its laser induced fluorescence spectrum are compared with those of a samarium pentaphosphate crystal (SmP₅O₁₄). Findings include: (i) The crystal field splitting of the energy levels responsible for fluorescence in SmP₅O₁₄ at room temperature is consistent with the local symmetry of oxygen atoms of the phosphate cage around the Sm³⁺ ions being quite close to cubic – in accord with crystal structure. At 12 K there is a systematic disappearance of the shortest wavelength lines of each fluorescence band attributable to a decreasing population of higher crystal field levels, which are occupied at ambient temperature. (ii) The (Sm₂O₃)_0.248(P₂O₅)0.752_0.248 glass fluorescence spectrum forms five bands, which can be related to that of the crystal but with inhomogeneous line broadening; the short wavelength edges sharpen at low temperatures, also attributable to a decreasing population of higher crystal field levels at lower temperatures. (iii) The shifts (d/dp) in the wavelengths of the fluorescence peaks of the SmP₅O₁₄ crystal induced by pressure up to 50 kbar in a diamond anvil cell are small but measurable at room temperature, being about +0.03 nm kbar^–1 (+0.3 Å kbar^–1). Application of pressures up to 50 kbar to the (Sm₂O₃)_0.248(P₂O₅)_0.752 glass did not alter the positions of the bands within the error in the fluorescence wavelength measurements. Neither the SmP₅O₁₄ crystal nor the metaphosphate glass showed any indication of undergoing a phase transition up to the highest pressure reached. A low frequency Raman mode has been observed, which softens with reducing temperature, indicating softening of the associated optical mode and suggesting that, like other RP₅O₁₄ crystals, SmP₅O₁₄ undergoes a ferroelastic phase transition.     

The optical properties of amorphous V2O5 and SiO thin films and of the mixed dielectric system SiO/V2O5

The optical absorption of amorphous thin films of V₂O₅, SiO and of SiO/V₂O₅ is studied in the photon energy range 0.42 to 6.53 eV. The optical absorption edge of evaporated V₂O₅ films can be described by direct forbidden transitions while that of SiO films follows the non-direct transitions in k-space. The data of the SiO/V₂O₅ oxide mixtures are fitted to new values of the exponent in the well-known absorption equation and the corresponding optical band gaps are determined. Experimental data on the wavelength dependence of the refractive index of SiO films are presented. The dispersion of the refractive index follows a single oscillator model. The infrared spectra show that some bonding occurs between the two oxides so that the mixed dielectric system SiO/V₂O₅ cannot be considered as a simple physical mixture.     

Acoustic and optical Debye temperatures of the vitreous system CoO-Co2O3-P2O5

For the Co-P-O glass system, data have been assembled on acoustic Debye temperatures obtained from ultrasonic wave-velocity measurements, acoustic and optical Debye temperatures determined from infrared absorption studies, and optical Debye temperatures obtained from electrical conductivity measurements. It is argued that these quantities are systematically related in theory, and the relationships are substantiated by the experimental data.On leave from the Physics Department, Faculty of Science, Monofia University, Shebeen El-Kome, Egypt.     

Infrared properties of the vitreous system TeO2-ZnCl2

Journal of Materials Science Letters -     

Thermal conductivity of the vitreous system (ZnO) x −(P2O5)1−x

Glasses of the system (ZnO)_x–(P₂O₅)_1–x have been prepared by melting ZnO with anhydrous P₂O₅ in open crucibles. These glasses had compositions ranging from 20 to 70 mol % ZnO (chemically analysed ZnO mol %). Measurements of the thermal conductivity for the present glass system have been made in the temperature range 305 to 630 K. The thermal conductivity of this glass system is mainly due to lattice thermal vibrations. The thermal conductivity data are found to be fairly sensitive to the ZnO mol % content. It is observed from these data that the present glass system can be divided into three compositional regions. This behaviour is qualitatively explained in terms of changes in glass structure.     

Compositional dependence of infrared absorption spectra studies for TeO2-P2O5 and TeO2-P2O5-Bi2O3 glasses

The infrared absorption spectra of the vitreous TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ systems are studied in the spectral region of 4000 to 200 cm^–1. Absorption bands in this range are assigned. The midband wavenumber and the absorption intensity for the attributed bands are found to be strongly and systematically dependent on glass composition. Quantitative analysis was also attempted to justify our attribution of the observed bands.     

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1–x)P₂O₅ vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO ₄ ^3– and P₂O ₇ ^4– , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH₄H₂PO₄ by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P₂O₅, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm^–1, assigned to the bending and stretching modes in H₂O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1–x)P₂O₅ system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm^–1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb²⁺ takes place. The ionic character of the phosphate groups, P-O^(–), PO ₄ ^3– is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm^–1 respectively. The maximum intensity of the P-O^(–) band at 1120 cm^–1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO ₄ ^3– , P₂O ₆ ^2– and P₂O ₇ ^4– for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm^–1 region attributed to the v₃-mode in PO ₄ ^3– , suggests a gradual transformation of PO ₄ ^3– units to PO ₃ ^– groups in lead meta-phosphate glass and then their restoration to PO ₄ ^3– groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O^(–), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.     

Electron spin resonance studies of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

Electron spin resonance studies of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ amorphous thin films have been made. For lower molar contents of B₂O₃, the co-evaporated V₂O₅/B₂O₃ films show poorly resolved hyperfine structure, whereas for higher content of B₂O₃ the hyperfine spectra are well resolved. This behaviour of films is attributed to the increase in the lifetime of a particular V⁴⁺ ion due to Anderson localization of charge, as the degree of disorder increases with increase in the molar content of B₂O₃. The unpaired electron at a given time is localized on a single ⁵¹V nucleus. The low intensity of ESR signal for higher concentration of V₂O₅ in the co-evaporated V₂O₅/B₂O₃ films has been related to the less effective concentration of V⁴⁺ ions due to antiferromagnetic coupling of the V⁴⁺ ions.     

Electrical conduction through MIM structures of evaporated V2O5 and V2O5/B2O3 amorphous thin films

The electrical conduction through vacuum-evaporated thin films of V₂O₅ and V₂O₅/B₂O₃ in MIM structures has been investigated. The high-field behaviour of both types of film is in accordance with the Poole-Frenkel type of mechanism. The increase in B₂O₃ content in co-evaporated V₂O₅/B₂03 films results in a decrease in the conductivity of the composite films. This is attributed to the expansion of the resultant film structure due to the network-forming effect of B₂O₃. The covaporated thin films of V₂O₅/B₂O₃ with a molar content of B₂O₃ larger than 40% are observed to be unstable because of their hygroscopic nature.     

X-ray photoelectron spectroscopic studies of evaporated V2O2and co-evaporated V2O5/B2O3 films

X-ray photoelectron spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been investigated. The photoelectron spectrum of a simple V₂O₅ film shows the splitting of the V 2p level in accordance with the spins. The values of binding energies corresponding to V 2p and O1s are comparable with those reported previously. For co-evaporated V₂O₅/B₂O₃ films a chemical shift in the O 1s level has been observed which has been attributed to the changed chemical environment of oxygen as a result of the presence of boron and vanadium atoms. The values of binding energies for V 2p_3/2 and O 1s corresponding to simple evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ show the presence of V₂O₄ species in the films.     

Some physical properties of V2O5-Fe2O3 and V2O5-Fe2O3-Li2O systems

Various methods have been used to study the physical properties of the V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems, including X-ray, electron microscope, Mössbauer effect, NMR and thermogravimetric measurements. The iron ions are approximately equally distributed in substitutional and interstitial sites in the V₂O₅ lattice. The maximum number of iron ions dissolved in the V₂O₅ matrix corresponds to 4 mol % Fe₂O₃. In all the samples a quantity of Fe₂O₃ which has not been included in lattice is observed. The V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems are formed from solid solutions mixed with very small Fe₂O₃ particles. The analysis of the charge compensation of iron ions suggests that V₂O₅ is a quasi-amorphous semiconductor. Irradiation of V₂O₅-based samples with an electron beam induces the V₂O₅ platelets to convert to the VO _x phase.     

Preparation and thermoelectricity of TiO2/V2O5 powders

TiO₂/V₂O₂ powders were prepared by the mixed oxide and sol-gel method. The sols were dried using different procedures. The obtained powders were characterized by X-ray diffraction, scanning electron microscopy, BET-adsorption and laser granulometry. The electric properties were determined by measuring the thermoelectric power. A strict correlation of the thermoelectric power and the V₂O₂ content could be observed, but by contrast to conductivity measurements, the thermoelectric power was not influenced by the powder morphology. Additionally, the thermoelectric power was drastically influenced by the calcination temperature.