Electrical properties and internal friction in vanadium phosphate glasses

The electrical properties and internal friction in the glasses of (50–80)V₂O₅ · (50-20)P₂O₅ and 70V₂O₅ ·xB₂O₃ · (30–x)P₂O₅ were measured. In both system glasses, one peak on internal friction was observed in the temperature range of –100 to 200° C at a frequency of about 1 Hz. The area of the internal friction peak increased with increasing valence ratioR, similar to those in the d.c. conductivity and dielectric increment. Frequency temperature dependence of dielectric loss peak and peak on internal friction showed a parallel line, and its activation energy was 0.33 eV. From the above results, the peak observed at internal friction was due to the hopping of localized electrons in small polarons.     

Electrical conductivity and optical properties of gamma-irradiated niobium phosphate glasses

A detailed study of the d. c. electrical conductivity and the optical absorption spectra as a function of gamma-irradiation doses for prepared (20 mole% Nb₂O₅ –80 mole% P₂O₅) glass system is presented. The temperature dependence on the d. c. electrical conductivity measurements is studied over the temperature range from room temperature to 573 K. The induced changes in the d. c. electrical conductivity caused by different doses of gamma irradiation (0–16 Mrad) were studied. The electrical conductivity, , and the activation energy, E, values were found to be sensitive to the gamma-ray doses. The optical absorption spectra were measured in the wavelength range from 200 to 1100 nm at different -doses, in the range from 0 to 28 Mrad. The obtained results are analysed assuming optical absorption by indirect transition. Values of the absorption coefficient, , the optical energy gap, E _opt, and the width of the band tail, E, are found to be -irradiation dose dependent.     

Electrical conductivity of zinc-barium phosphate glasses

A series of binary and ternary zinc-barium phosphate glasses was prepared, their densities were measured and their electrical properties were studied. A linear dependence of density with BaO content was observed in barium phosphate glasses while a breaking point in the linearity of the density curves occurs at about 40% ZnO concentration for the zinc-barium phosphate glasses. The d.c. conductivity measurements show that the activation energy is increased when P₂O₅ is replaced by BaO or ZnO, respectively. In the ternary glasses the activation energy appears to be relatively unaffected when BaO is replaced by ZnO, but at approximately 40%ZnO, there is a rise in the value of activation energy. Such a pronounced change in density and activation energy could be due to the change in the coordination of ZnO in this region. The linear log -1/T curves and also the value of _o suggest that the conduction mechanism in these glasses is similar to those in many other oxide glasses that have been investigated.     

Electrical properties of barium-borosilicate glasses

Bulk and thin-blown films of barium-borosilicate glass were prepared and their electrical conduction properties at high and low fields were measured as functions of temperature. The electrical conductivity is an exponential function of inverse temperature at high temperatures with an activation energy in the range 1.0 to 1.4 eV, depending on composition. The conduction process is believed to involve polarons hopping in the adiabatic regime. Some high-field electroforming effects are observed.     

Electrical transport studies in alkali iron phosphate glasses

The electrical properties of xFe₂O₃−(100 −x) Na₂P₂O₅ glasses with x = 0, 6, 12, 18 and 24 mol% have been studied in the temperature range from 323 to 573 K. The dc conductivity was found to decrease as the iron content increases while the activation energy increases with increasing iron content in the glasses. In the high—temperature regime above θ_D/2 (θ_D is the Debye temperature), the Mott model of small polaron hopping (SPH) between nearest neighbors is consistent with the conductivity data. The electron—phonon interaction coefficient γ_P was very large (66.74–97.60). The electrical conduction of the glasses was confirmed to be non-adiabatic small polaron hopping. The physical parameters obtained by fitting the experimental results to these models are consistent with glass compositions.     

Electrical and physicochemical properties of some Ag<Subscript>2</Subscript>O-containing lithia iron silica phosphate glasses

The present paper reports the influence of Ag₂O addition at the expense of Li₂O on the local structure of xAg₂O·(30 − x)Li₂O·10Fe₂O₃·10SiO₂·50P₂O₅ glass matrix (with x = 0, 0.5, 1, 1.5 and 2 mol %). The phosphate structural units of the network former are assessed from Fourier transform infrared (FT-IR) spectroscopy. The addition of Ag₂O to the glass network matrix ≤1 mol % leads to the occurrence of a depolymerization process of the phosphate structure and consequently, to the appearance of a distortion of the PO₄ tetrahedra. When the content of Ag₂O is increased from 1.5 up to 2 mol %, a remarkable polymerization process has been observed. The density, molar volume, microhardness and chemical durability have been investigated in order to study the effect of Ag₂O/Li₂O replacements on the physicochemical properties the studied glasses. The AC electrical properties are affected to a great extent with composition. These results are related to the internal structure of the glass samples. The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 100 Hz–100 kHz and the effect of compositional changes on the measured properties was investigated. Measurements showed that the electrical responses of glass samples were different and complex for interpretation. The increase of Ag₂O addition at the expense of Li₂O contents (from 0 to 1 mol %) led to increase the conductivity, dielectric constant and dielectric losses of samples. The addition of more Ag₂O at the expense of Li₂O (from 1.5 to 2 mol %), resulting into decreasing the conductivity, the dielectric constant and dielectric losses of the studied glasses. The experimental data of the glass samples were argued to the internal structure of the glasses and the nature and role-played by weakening or increasing the rigidity of the structure of the sample. It could be concluded, therefore, that the AC electrical properties of the samples were influenced by the distribution of its constituents, connectivity, and number of free charges.     

Gamma-ray dosimetric properties of molybdenum phosphate glasses

In the present work, a study of the temperature dependence of the d.c. electrical conductivity and conduction activation for a series of MoO₃-P₂O₃ glass systems has been carried out. The conductivity measurements of the unirradiated glass specimens proved to be mainly dependent on both temperature and transition metal ion content in the glass matrix. The results of the present investigation have shown that the conduction mechanism would be due to the electron exchange between the low and high valency states of the MoO₃ oxide (Mo" and Mo⁶⁺). The radiation-induced conductivity of the glass system studied, produced by gamma rays, has also been measured experimentally. The d.c. electrical conductivity has proved to be dose dependent, which showed a decrease with increasing -dose. The results reflect some evidence of the-ray dosimetric potential of the glass specimens studied.     

Dielectric properties of some berate glasses

The dielectric constant, epsilon', and the dielectric loss, epsilon ", for some selected lead berate glasses within the frequency band 10(5) to 10(7) Hz and the temperature range (20 similar to 50)degreesC were measured. The dielectric dispersion and the dielectric loss absorption bands were observed. the relaxation time, the activation enthalpy and entropy change of the dielectric relaxation were calculated. The results obtained were discussed and correlated to the internal network structure of the glasses studied.     

Electrical conduction in copper phosphate glasses containing nickel or cobalt

A variation in d.c. conductivity and activation energy of 35 mol%CuO-65mol%P₂O₅ glasses is observed as CuO is gradually replaced by NiO or CoO. These results are believed to be due to the change in the redox ratio of the two transition metal oxide glasses, which causes an increase and then a decrease of polaron hopping transitions between the ions of the same element and between the ions of the different transition metal elements.     

Optical and ultrasonic properties of europium phosphate glasses

To provide an overall picture of the vibrational properties of phosphate glasses containing high concentrations of europium, measurements have been made of their ultrasonic wave velocities and attenuation, optical absorption spectra and laser-induced fluorescence. To examine their valence state, the fluorescence of the glasses has been examined. The spectra do not show any obvious sign of divalent europium ions, only trivalent europium ion fluorescence being observed. Room-temperature absorption spectra of these glasses also provide evidence of only the absorption bands of trivalent europium. The elastic stiffnessesC ₁₁ andC ₄₄ continue to increase down to low temperatures and the ultrasonic attenuation is characterized by a broad peak, properties which are consistent with thermally activated relaxations of two-level systems. The longitudinal and shear ultrasonic wave velocities decrease under pressure; the hydrostatic pressure derivatives (C ₁₁/P) _{T, P=0} and (C ₄₄/P) _{T, P=0} of the elastic stiffness tensor componentsC _IJ and (B/P) _{T, P=0} of the bulk modulus,B ₀, are negative. When compressed, the europium phosphate glasses, like their samarium analogues, show the interesting property of becoming easier to squeeze. Measurements, using a pulse superposition technique, of the effect of uniaxial stress on ultrasonic wave velocities have been used to determine the temperature dependences of the third-order elastic stiffness tensor components of (Eu₂O₃)_0.186(P₂O₅)_0.814 and (Eu₂O₃)_0.20(P₂O₅)_0.80 glasses between 77 and 400 K. The uniaxial and hydrostatic pressure dependences of the elastic constants quantify the cubic term in the strain Hamiltonian and the vibrational anharmonicity of the long-wavelength phonons of these glasses. The acoustic mode Grüneisen parameters are negative: application of pressure induces a decrease in the long-wavelength acoustic phonon mode frequencies. As the temperature is reduced the pressure-induced mode softening becomes enhanced. The hydrostatic pressure derivative (C ₁₁/P) _{T, P=0} is larger than (C ₄₄/P) _{T, P=0} over the whole temperature range, and the longitudinal acoustic mode Grüneisen parameter _L is larger than that _S of the shear wave: the longitudinal mode softens more with pressure than the shear mode. Murnaghan's equation-of-state is used to determine the compressionV(P)/V ₀.