Conductivity, dielectric, and structural studies of (30-x) SrO-xBaO-10Al2O3-45SiO2-5B2O3-10Y2O3 (5 ≤ x ≤ 25) glasses (original) (raw)
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2018
The phase formation, microstructural evolution and dielectric properties of SrO-B2O3-SiO2 (SBS) and BaO-SrO-Nb2O5-B2O3-SiO2 (BSNBS) glasses were studied. SBS and BSNBS glasses were prepared via solid state reaction method. The raw materials of SBS and BSNBS were wet mixed for 24 hours and then dried overnight in oven. The mixing powder of SBS and BSNBS were heated until 1250 °C and 1450 °C, respectively for 2 hours for making a glass. The glass frits was crushed to form a fine powder. SBS and BSNBS glass powder was compacted at 250 MPa and then were heat treated at 800 °C and 650 °C, for 3 hours respectively. X-ray diffractometer (XRD) analysis showed the amorphous phase for both glasses powder after melting process, whereas the formation of Ba0.39Sr0.61Nb2O6, SiO2 and Nb2O5 phases, respectively were obtained by BSNBS sample after heat treatment process. Observation on scanning electron microscopy (SEM) micrographs showed no grain was observed for SBS sample while fine grain was seen for BSNBS sample. Both dielectric constant and dielectric loss of BSNBS glass was higher compared to the SBS glass.
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Temperature and frequency dependencies of DC and AC conductivities, dielectric response, static permittivity, optical absorption edge, infrared absorption spectrum, density, and temperatures of glass transition and crystallization for lithium molybdenum-antimonite glasses, (80 − x)Sb 2 O 3 -20Li 2 O-xMoO 3 , where x = 0-40, are measured and discussed. The DC conductivity increases with increasing concentration of MoO 3 . At 150°C, it ranges from 5 × 10 −11 S/m up to 3 × 10 −8 S/m. Polaron hopping between Mo 5+ and Mo 6+ ions contributes, probably, to the DC conductivity. Ionic conductivity by Li + ions is also present. The conduction activation energy monotonously decreases from 1.15 eV, at x = 5, down to 0.91 eV, at x = 40. In all glasses with x N 0, the conduction activation energy is close to a half of the indirect allowed optical gap. The pre-exponential factor, σ 0 , goes through a sharp maximum close to the composition (x = 20) with both the highest glass transition temperature and the largest thermal stability range. The frequency dependence of the AC conductivity is composed of three componentsthe DC conductivity and two AC components. For x = 35 and 40, the activation energy of electrical relaxation is equal to 0.954 ± 0.008 eV and the pre-exponential factor of relaxation times is equal to (4 ± 1) 10 −14 s. The static relative permittivity ranges from 17.4 to 23.0. Strong extrinsic absorption bands in infrared region originate from hydroxyl ions, CO 2 impurities, and silicon-oxygen vibrations. The UV-visible indirect allowed absorption edge shifts from 2.6 eV to 2.1 eV with increasing MoO 3 content. With increasing MoO 3 content the glasses darken, from a light yellow color, at x = 0, to a deep brown color, at x = 40.
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The present paper studies the dielectric properties and ac conductivity of sodium borosilicate glasses doped with varying concentrations of Gd 2 O 3 , while maintaining the SiO 2 :Na 2 O:B 2 O 3 ratios constant for all compositions. The samples were prepared using rapid quenching method. Their dielectric and electrical properties were measured in the frequency range (10 2 -10 6 Hz) and temperature range (298-523 K). Experimental results showed that all dielectric and electrical properties are dominated by mole% of Gd 2 O 3 . The decrease and increase in these properties were found to be due to formation of short range ordered structure and non-bridging oxygen, respectively. Different models were suggested to describe the conduction mechanism of the investigated compositions based on mole% of Gd 2 O 3 . Correlated barrier hopping model (CBH) was suggested to describe the conduction mechanism of 0-2.52 mole% Gd 2 O 3 doped -samples. While, overlapping large polaron tunneling (OLPT) model was applied to describe conductivity of 2.83 mole% Gd 2 O 3 doped sample.
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The samples of composition 60V 2 O 5-5P 2 O 5-(35−x)B 2 O 3-xCeO 2 , x = 1, 2, 3, 4 and 5 mol% were prepared by the melt-quench method. The prepared samples were characterized by X-ray diffraction, thermogravimetric-differential thermal analysis and impedance spectroscopy. The activation energies were evaluated using glass transition temperature (T g) and peak temperature of crystallization (T c). The dependence of activation energy on composition was discussed. AC conductivity of samples has been analysed. Electrical conductance and capacitance were measured over a frequency range of 20 Hz-1 MHz and a temperature range of 303-473 K. At room temperature, maximum value of electrical conductivity was observed to be 0.0024 S cm −1 for x = 1. The samples show semiconducting features predominantly based on an ionic mechanism.
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Glass samples of a mixed alkali borate glasses doped with cobalt oxide have been prepared by the melt quenching technique in air atmosphere. The glassy state of the samples is characterized using X-ray diffraction. Glass-transition temperatures are measured using differential scanning calorimetery (DSC). A.C. Conductivity (σa.c), real and imaginary parts of the impedance of the prepared samples have been measured in the frequency range (42Hz-5MHz). The measurements were carried out in the temperature range (303-468K). The total conductivity as well as the frequency exponent, S, were determined from the dielectric spectrum, also the activation energy was calculated and discussed.
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Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb2O3–V2O5–K2O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb2O3–30V2O5–40K2O and 70Sb2O3–30K2O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb2O3 concentration increases.
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The AC conductivity and dielectric parameters of the glassy system of (70-x) V 2 O 5 ·x(Zn/Pb)·10SrO·20FeO (x = 0, 5, 10, and 15) glasses have been investigated. The frequency and temperature dependence of dielectric constant (ε) and dielectric loss (ε) is studied in the frequency range 100 Hz-5 MHz and in the temperature range 300-460 K. Dielectric dispersion is observed in all samples as Zn/Pb increase content in the (70-x)V 2 O 5 ·x (Zn/Pb)·10SrO·20FeO systems. These results are explained on the basis of a Debye-type relaxation. It is also observed that the activation energy increases on increasing the Zn/Pb contents in this system.
Journal of the European …, 2004
Vitrification and crystallization properties of glasses of the system BaO-TiO 2 -PbO-Al 2 O 3 (B 2 O 3 ) were investigated. The fields of vitrification based on ternary diagrams of BaTiO 3 -PbTiO 3 -(TiO 2 +Al 2 O 3 +B 2 O 3 ) with varied contents of Al 2 O 3 (10, 13, 16 mol.%) and B 2 O 3 (3, 15 mol.%) were identified. The glass compositions obtained had relatively low melting temperature (%1450 C). These stable glasses could be thermally treated to produce glass-ceramics characterized by fine-crystalline structures and regulated permittivity associated to the contents of ferroelectric phases. The phase composition of such glass-ceramics included different Pb x Ba 1-x TiO 3 solid solutions depending on the starting chemical composition. Permittivity of the obtained materials (f=800 kHz, T=25 C) varied from 20 to 680 relatively to the time of crystallization. #