Electrical, dielectric, and optical properties of Sb2O3–Li2O–MoO3 glasses

International audienceTemperature 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)Sb2O3–20Li2O–xMoO3, where x = 0–40, are measured and discussed. The DC conductivity increases with increasing concentration of MoO3. At 150 °C, it ranges from 5 × 10− 11 S/m up to 3 × 10− 8 S/m. Polaron hopping between Mo5 + and Mo6 + 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 > 0, the conduction activation energy is close to a half of the indirect allowed optical gap. The pre-exponential factor, σ0, 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 components — the 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, CO2 impurities, and silicon–oxygen vibrations. The UV–visible indirect allowed absorption edge shifts from 2.6 eV to 2.1 eV with increasing MoO3 content. With increasing MoO3 content the glasses darken, from a light yellow color, at x = 0, to a deep brown color, at x = 40

Local atomic structure and electrical properties of Ge20Se80−xTexGe_{20}Se_{80−x}Te_x (x=0, 5, 10, and 15) glasses doped with Ho

Measurements of ac and dc conductivities, complex electrical modulus, static permittivity, dielectricrelaxation, and X-ray diffraction of the glassy system Ge20Se80xTex (x = 0, 5, 10, and 15), ‘‘pure’’ anddoped with 1000–2000 wt.-ppm Ho (added as metal or oxide), are presented and discussed. Influenceof crystallization and/or phase separation on these properties is described.Temperature dependences of the dc conductivity are Arrhenius-like; their conduction activation energyincreases (0.73–0.84 eV) and the dc conductivity decreases (1.51068108 S/m, at 60 C) withdecreasing concentration of Te. Doping with Ho3+ ions in a metallic form decreases the conduction activationenergy. Relative static permittivity of glasses ranges from 9.6 to 12.8. The highest values are foundin heavily doped, partly crystallized glasses. The lowest values are found in ‘‘pure’’ glasses with a highcontent of Te. At 1000 wt.-ppm Ho, modular diagrams are almost semicircular, modular spectra areDebye-like, and their shape is independent on temperature. At 2000 wt.-ppm Ho, two relaxation processesappear and the shape of both modular diagrams and modular spectra depend on temperature. Apartial crystallization takes place in these glasses.For heavily doped glasses (1500 and 2000 wt.-ppm Ho), XRD experiments, using high-energy photons,show distinct Bragg peaks stemming from a tiny fraction (about 0.25%) of crystalline phases. Crystallinecomponent is rather homogeneously distributed within the sample. Changing level of Ho doping affectsthe short-distance arrangement in glasses. A higher level of Ho doping implies shortening of the interatomicdistances, higher mean atomic density, and higher coordination numbers what suggests betteratomic packing

Lithium and lead chloride antimonate glasses

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Pula students’ television competencies

Educators and teachers’ media competencies are a prerequisite for children and youth’s successful media use as future active democratic citizens. In Croatia, however, they are not yet systematically acquired and are mostly studied in general, in elementary schools, while student populations and television competencies are marginalized. Therefore, we conducted a quantitative empirical study of future educators and teachers’ television competencies on a sample of the 140 first-year undergraduate students of the Juraj Dobrila University of Pula. The data were collected by a questionnaire while descriptive and inferential statistics were used in the processing of the collected data. The results show students’ low TV competencies in general and a difference in relation to the study and educational module. Students studying Preschool Education (which includes the Media Culture course) are more competent than their colleagues are, while future teachers have less TV competencies than others do. Such an outcome highlights the need to upgrade the university curricula for educators and teachers