$(PbO)_{0.20-x}(Bi_20_3)_{0.40}:(Ti0_2)x$, $0.0 \leq x\leq 0.02$ glasses were prepared. Dielectric properties (dielectric constant $\varepsilon^{\prime}$, loss tan $\delta$ and a.c. conductivity ...$\sigma_{ac}$, over a wide range of frequency and temperature), optical absorption, ESR and IR spectra of these glass materials have been investigated. The dielectric study has revealed that the glasses possess high insulating strength when $TiO_2$ concentration is >0.8 mol% in the glass matrix. The optical absorption spectra of these glasses exhibited bands due to $Ti^{3+}$ ions in the visible region. ESR spectral studies have also indicated that a fraction of $Ti^{4+}$ ions reduced to $Ti^{3+}$ ions. IR spectra of these glasses exhibited bands due to $TiO_4$ and $TiO_6$ structural units. Quantitative studies indicate that as concentration of $TiO_2$ is increased to 0.8 mol% in the glass matrix, a large proportion of titanium ions exist in $Ti^{3+}$ state and has influenced the physical properties of these glasses to a substantial extent.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Accuracy in complex dielectric permittivity calculations in binary dielectric mixtures in two-dimensions are reported by taking into account the shape of the inclusion phase. The dielectric ...permittivity of the mixtures were calculated using the finite element method, and the permittivities were estimated by two different procedures. The results were compared with those of analytical models based on a mean field approximation and regular arrangement of disks. We have approached the problem emphasizing the finite-size behavior in which regular polygons with n sides were assumed to mimic the disk inclusion phase. It was found that at low concentrations, < 30%, decagon-approximated circles (n = 10) cause an error of < 0.1% in the effective medium quantities compared with results obtained using analytical models.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this study, quasi-optical scattering of finite source electromagnetic waves from a dielectric coated cylindrical surface is analysed with Physical Optics (PO) approach. A linear electrical current ...source is chosen as the finite source. Reflection coefficient of the cylindrical surface is derived by using Geometrical Theory of Diffraction (GTD). Then, with the help of this coefficient, fields scattered from the surface are obtained. These field expressions are used in PO approach and surface scattering integral is determined. Evaluating this integral asymptotically, fields reflected from the surface and surface divergence coefficient are calculated. Finally, results obtained in this study are evaluated numerically and effects of the surface impedance to scattered fields are analysed. The time factor is taken as j te? in this study.
Deneysel dielektrik sab itleri kullanılarak okzalik asit çözeltilerinin 20 °C de ve farklı çözücülerde h azırlanan çözeltilerinin dipol momentleri belirlenmiştir. Okzalik asitin dipol monıenti ...üzerine çözücüterin etkisi tartışılmıştır. Diğer önemli fiziksel nicelikler olan kırma indisleri, yoğunluklar ve dielektrik sabitleri de bel ir lenmi ştir.
The ac conductivity and dielectric properties of glassy system SexTe79 - xGe21, with x = 11, 14, 17 at.%, has been studied at temperatures 300 to 450 K and over a wide range of frequencies (50 Hz to ...500 kHz). Experimental results indicate that the ac conductivity and the dielectric constants depend on temperature, frequency and Se content. The conductivity as a function of frequency exhibited two components: dc conductivity s dc, and ac conductivity s ac, where s ac \sim w s. The mechanism of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model (CBH). The activation energies are estimated and discussed. The dependence of ac conductivity and dielectric constants on the Se content x can be interpreted as the effect of Se fraction on the positional disorder. The impedance plot at each temperature appeared as a semicircle passes through the origin. Each semicircle is represented by an equivalent circuit of parallel resistance Rb and capacitance Cb.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
By employing the method of electrostatic potential expansion, the interface optical (10) and surface optical (SO) phonon modes and the corresponding Fröhlich-like electron-phonon-interaction ...Hamiltonian in a QID wurtzite cylindrical quantum well wire (QWW) embedded in nonpolar dielectric matrix are derived and studied based on the dielectric continuum model and Loudon's uniaxial crystal model. Numerical calculations for a wurtzite GaN/AIN QWW are mainly focused on the size- and dielectric-dependent IO and SO phonon spectra and electron-IO (SO)phonons coupling functions. Results reveal that, in general, there are two branches of IO phonon modes and one branch of SO mode in the system. The dispersions of the IO and SO modes are obvious only when the radii ratio $\beta$ and the dielectric constant of nonpolar matrix ea is small. The limiting frequencies of IO and SO modes for very large (5 have been analyzed in depth from both physical and mathematical viewpoints. The reducing behaviors of some modes have been clearly observed. Via the discussion of electrostatic potential spacial distributions of the IO and SO modes, we find that the QWW structures and dielectric constants of nonpolar matrix have little influence on the low-frequency IO mode, but they can greatly affect the potential distributions of high-frequency IO mode and SO mode. Detailed comparison of the dispersion behaviors of the modes and electron-phonon coupling properties in the QID wurtzite QWWs with those in wurtzite QWs and cubic quantum dots has also been made. Furthermore, part of the theoretical results derived in the present paper is consistent with the relatively experimental conclusion.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
$Li_2O-Fe_2O_3-P_2O_5$ glasses containing small concentrations of $Ag_2O$ from 0 to 2 mol% were prepared. Samples are characterized by X-ray diffraction and scanning electron microscope techniques. A ...number of studies viz., chemical durability, dielectric studies (constant $\varepsilon'$, loss tan $\delta$, a.c. conductivity $\sigma_{ac}$ over a range of frequency and temperature), spectroscopic (infrared, optical absorption ESR spectra) and magnetic susceptibility studies of these glasses, have been carried out. The interesting variations observed in all these properties with the concentration of $Ag^+$ ions have been analyzed in the light of different oxidation states and environment of iron ions in the glass network.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper reports optical properties of amorphous chalcogenide thin films of $As_2Se_3$ of different thicknesses 2000-6800 ˚A. The transmittance and reflectance of thin films were measured in ...the wavelength
range 500-1000 nm. It was found that the optical band gap increases with film thickness. Variation of refractive index n and extinction coefficient k with thickness have been studied to analyze optical efficiency of the $As_2Se_3$ thin films. The dielectric behavior of the films has also been studied and high
frequency dielectric constants ε∞ has been estimated as a function of thickness of films.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Dielektrik geçirgenliği ve elektrik iletkenliği kil minerallerinin elektrokinetik özelliklerini belirlemek için kullanılabilir. Bu anlamda, kaolen ve bentonit minerallerinin dielektrik geçirgenliği ...ve elektrik iletkenlği, farklı NaCl içeriğinde ve mineral/su oranında 0.1 kHz- 13 MHz frekans aralığında saptandı. Sonuçlar gösterdi ki, genelde, kaolen ve bentonit benzer dielektrik geçirgenlik özelliği gösteriyor: ölçüm yapılan frekans arttıkça mineral-su karışımının dielektrik geçirgenliği azalıyor. İyon konsatrasyonu arttıkça, mineral-su karışımının dielektrik geçirgenliği düşük frekanslarda (kHz) artıyor, yüksek frekanslarda azalıyor (MHz). Sistemdeki iyon konsantrasyonu arttıkça hem kaolenin hem de bentonitin elektrik iletkenliği artmaktadır. Kaolen/su oranı arttıkça elektrik iletkenliği azalmakta fakat bentonit/su oranı arttıkça elektrik iletkenliği artmaktadır. Bu olay bentonit/su karışımında yüzeysel iletkenliğin olduğunu göstermektedir. Bu çalışmanın sonuçları gösteriyorki dielektrik geçirgenliği ve elektrik iletkenliği ölçülerek kil minerallerinin elektrokinetik davranışı belirlenebilir. Yine benzer şekilde yeraltı kirlenmesinin oluşup oluşmadığı veya uygulanan yer altı temizleme yönteminin etkin olup olmadığı benzer şekilde tespit edilebilir.
The electrical conductivity and dielectric permittivity of clay-water systems were used to characterize the physicochemical state of kaolin and bentonite-water systems. The dielectric permittivity and electrical conductivity of kaolin and bentonite were determined at various water contents and NaCl concentrations as a function of frequency, ranging from 0.1 kHz to 13 MHz. The results indicate that kaolin and bentonite have similar dielectric behavior. An increase in the frequency produces a decrease in the dielectric permittivity of the soil-pore water mixture. As the ion concentration increases, the dielectric permittivity of the mixture increases at low frequency (kHz) whereas it decreases at high frequency (MHz). The electrical conductivity of kaolin and bentonite increases with an increase in the ion concentration in the soil-water mixture. The electrical conductivity of a kaolin-water mixture decreases with an increase in the solid concentration. In contrast, the electrical conductivity of a bentonite-water mixture increases with a decrease in the solid concentration. This indicates the importance of the surface conductivity of a bentonite-water mixture. Furthermore, the results of this study indicate that dielectric permittivity and electrical conductivity might be used to characterize the electrokinetic behavior of soil minerals to determine the physiochemical changes in clay soil-water systems, such as subsurface contaminations.
Bu çalışmada, sonlu kaynaklı elektromagnetik dalgaların, dielektrik kaplanmış silindirik bir yüzeyden optik gibi saçılması Fiziksel Optik (FO) yaklaşımı ile incelenmiştir. Sonlu kaynak, çizgisel ...elektrik akım kaynağı olarak seçilmiştir. Silindirik yüzeye ait yansıma katsayısı, Kırınımın Geometrik Teorisi (KGT) yaklaşımı kullanılarak bulunmuştur. Elde edilen bu katsayı kullanılarak yüzeyden saçılan alanlar ifade edilmiştir. Alan ifadeleri FO yaklaşımında kullanılmış ve yüzeye ait saçılma integrali belirlenmiştir. Bu integralin asimptotik olarak değerlendirilmesi sonucunda yüzeyden yansıyan alanlar ile yüzeye ait diverjans katsayısı hesaplanmıştır. Neticede, çalışmada elde edilen sonuçlar nümerik olarak değerlendirilmiş ve yüzey empedansının saçılan alanlara etkileri incelenmiştir. Yapılan çalışmada zaman faktörü ejt alınmıştır.
