Electron–Electron Interactions in Sb-Doped SnO<Subscript>2</Subscript> Thin Films

Electrical conductivity and Hall-effect measurements on undoped and Sb-doped SnO₂ thin films prepared by the sol–gel technique were carried out as a function of temperature (55 K to 300 K). Structural characterizations of the films were performed by atomic force microscopy (AFM) and x-ray diffraction (XRD). A doping-induced metal–insulator transition (MIT) was observed. On the metallic side of the transition, the experimental data were interpreted in terms of electron–electron interactions (EEI). The existence of EEI was confirmed by excellent agreement between theoretical and experimental data. The experimental data on the insulator side of the transition were analyzed in terms of variable-range hopping (VRH) conduction. A complete set of parameters describing the properties of the localized electrons, including hopping energy, hopping distance, and the value of the density of states at the Fermi level, was determined.     

A Study on Magnetoresistivity, Activation Energy, Irreversibility and Upper Critical Field of Slightly Mn Added Bi-2223 Superconductor Ceramics

This study discusses the effect of Mn addition on the superconducting and physical properties in Bi_1.8Pb_0.4Sr₂Mn _x Ca_2.2Cu_3.0O _y bulk superconductors with x=0,0.03,0.06,0.15,0.3, and 0.6 by means of the magnetoresistivity measurements. The magnetoresistivity of the samples prepared using the standard solid-state reaction method was measured for different values of the applied magnetic field strengths. The superconducting and physical properties of the samples such as the zero resistivity transition temperatures (T _c ), irreversibility fields (?? ₀ H _irr ), and upper critical fields (?? ₀ H _c2) were deduced from the magnetoresistivity curves. Moreover, thermally activated flux creep model was studied for activation energy (U ₀) values of the samples. According to the results of the measurements, not only were the T _c and U ₀ values of the samples found to decrease significantly but the ?? ₀ H _irr and ?? ₀ H _c2 values were also observed to reduce with the increase in the Mn addition, indicating that the doping degrades the physical and superconducting properties of the samples.     

Analysis of Indentation Size Effect on Mechanical Properties of Cu-Diffused Bulk MgB2 Superconductor Using Experimental and Different Theoretical Models

This study indicates the change of the electrical, microstructural, physical, mechanical and superconducting properties of Cu-diffused bulk MgB₂ superconductors by means of scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness and dc resistivity measurements. The samples are prepared at different annealing temperatures in the range from 650 to 850 ^°C. Electrical and superconducting properties of samples are estimated from the dc electrical resistivity measurements. Moreover, microhardness measurements are performed to investigate the mechanical properties. Further, phase composition, grain sizes and lattice parameters are determined from the XRD measurements. At the same time, the surface morphology and grain connectivity of the samples are examined by SEM investigations. The measurements conducted demonstrate that both the Cu diffusion into the MgB₂ system and the increment in the diffusion-annealing temperature increase the critical transition temperatures. Similarly, microstructure and grain size improve while the voids and porosity decrease with the increase of the diffusion-annealing temperature. In addition, the experimental results of the microhardness measurements are investigated using the Meyer’s law, PSR (proportional specimen resistance), modified PRS (MPSR), elastic-plastic deformation model (EPD) and Hays–Kendall (HK) approach. The obtained microhardness values of the samples decrease with the increase of the diffusion-annealing temperature up to 850 ^°C. The Hays–Kendall approach is found to be the most successful model describing the mechanical properties of the samples studied in this work.     

Free Vibration Analysis and Design of an Adhesively Bonded Corner Joint with Double Support

This study carries out the three dimensional free vibration analysis of an adhesively bonded corner joint and investigates the effect of an additional horizontal support to the adhesive corner joint with single support on the first ten natural frequencies and mode shapes. In the presence of a horizontal support the effects of the vertical support length, the adhesive thickness, the plate thickness, and the joint length on the natural frequencies and modal strain energies of the adhesive joint were also investigated using the back-propagation Artificial Neural Network (ANN) method and the finite element method. The natural frequencies and modal strain energies increased with increasing plate thickness, whereas an adverse effect was observed for increasing joint length. Both horizontal and vertical support lengths exhibited similar effects but the adhesive thickness had a negligible effect. The plate thickness and the joint length are dominant geometrical parameters in comparison with both horizontal and vertical support lengths. The proposed ANN models were combined with the Genetic Algorithm in order to determine the optimal corner joint in which the maximum natural frequency and minimum elastic modal strain energy are achieved for each natural frequency and mode shape of the adhesive corner joint and the optimal dimensions were given versus one geometrical parameter.     

Influence of Surface Finish on Flexural Strength and Microhardness of Indirect Resin Composites and the Effect of Thermal Cycling

This study investigated the effect of surface finish and thermal cycling procedures on flexural strength and surface microhardness of three indirect resin composites, Artglass®, Signum®, and Solidex®. The specimens were prepared in sufficient number and size according to flexural and microhardness test requirements (n = 10). Scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis was also used for studying the morphology, dispersion, and elemental compositions of fillers. The EDX results showed that Artglass contained 1.57% aluminium oxide (Al₂O₃), 53.29% silicon dioxide (SiO₂), and 2.62% barium oxide (BaO); Signum had 55.69% silicon dioxide (SiO₂) and Solidex had 44.99% silicon dioxide (SiO₂) of total mass. Artglass appeared to display the best flexural strength values under all the test conditions employed (range: 116.8 ± 32.18 to 147.8 ± 47.97 MPa), and it was followed by Signum (range: 93.7 ± 22.84 to 118.0 ± 33.45 MPa). Thermal cycling did not seem to have affected the flexural strength of Artglass and Signum (p > 0.05); however, it led to a significant decrease, from (110.5 ± 20.69 MPa) to 74.0 ± 13.30 MPa (p < 0.001), in the strength of polished Solidex specimens. While surface microhardness of the three materials increased by polishing (Artglass: 55.7 ± 2.64/74.1 ± 8.63 Vickers Hardness Numbers (VHN); Signum: 44.8 ± 3.12/60.7 ± 4.50 VHN; Solidex: 44.0 ± 2.31/53.4 ± 3.58 VHN for unpolished/polished specimens), thermal cycling had a deleterious effect on this property (p < 0.001).     

Effect of Argon Plasma Pretreatment on Tensile Bond Strength of a Silicone Soft Liner to Denture Base Polymers

This study evaluated the effect of argon plasma treatment on tensile bonding of heat-cured and auto-polymerized acrylic resins prior to the processing of a silicone soft liner. Both types of polymethylmethacrylate (PMMA) resins were treated with argon plasma for 1 min or 10 min (n = 5). A control group, including untreated resin specimens, was also formed. After processing of the soft liner, the specimens were deflasked and stored dry for 24 h, and they were then subjected to tensile bond strength testing. In order to see the plasma effect on the resin surface chemistry, representative specimens were analysed by XPS. Highest tensile bond strengths were observed in the 1-min exposure group for each resin, and 10-min exposure yielded the lowest bond strength likely due to the damaging effect of the plasma treatment. XPS analysis showed that the O/C ratios increased greatly in treated samples and that the binding energy values were not significantly changed.     

Properties of hybrid fiber reinforced concrete under repeated impact loads

Steel, glass and polypropylene fiber reinforced concrete structures were investigated under repeated impact loads in this study. Twelve different concrete series prepared fiberless the one of all and the others reinforced polypropylene, glass, steel and hybrid fiber were produced. The polypropylene fibers in diameter of 50 mm, l/d (length/diameter) ratio of 400, glass fibers in diameter of 14 mm, l/d ratio of 857 and steel fibers in diameter of 0.75 mm, l/d ratio of 80 were used in concrete mixtures. The volumetric contents were 0.5, 0.75 and 1% in fiber reinforced concrete. The volumetric content was 0.1% in polypropylene and glass fiber reinforced concrete. Drop-weight test similar the method presented ACI 544.2R-89 was conducted using 28 days cured samples having dimensions of 100 × 100 × 100 mm and reduction of strength were determined by ultrasonic pulse velocity (UPV) test. Furthermore, initial crack formation and fracture numbers variation in samples were detected. In the present study, it was aimed to develop performance under repeated impact loads using fibers in concrete. As a result, especially impact performance was rather increased in steel fiber reinforced concrete, and hybrid fibers had also positive effect on the performance of concrete.     

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB₂ superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T _c ) increase with increasing the diffusion-annealing temperature from 650 to 850?°C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850?°C. As for the XRD results, all the samples contain the MgB₂ phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81?×?10^?8 to 4.69?×?10^?7?cm²?s^?1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D?=?3.75?×?10^?3 exp (?1.15?±?0.10?eV/k _B T) and the corresponding activation energy of copper in MgB₂ system is found to be about 1.15?eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.     

Investigation of Structural and Superconducting Properties of Cr Added Bi-2212 Superconducting Ceramics

This study reports the effect of Cr addition on the structural and superconducting properties of Bi_1.8Sr_2.0CrxCa_1.1Cu_2.1O _y superconductor with x=0, 0.1, 0.3, 0.5 0.7, and 1 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and resistivity measurements. The samples studied in this work were prepared using the standard solid-state reaction method. Zero resistivity transition temperatures (T _c ) are qualitatively estimated from the dc resistivity measurements. The zero resistivity transition temperatures are obtained to decrease from 81 K to 53 K with the increase in Cr addition. Moreover, the phase and lattice parameters were determined from XRD measurements. Based on the refinement of cell parameters done by considering the structural modulation, the Cr addition was confirmed by an increase of the lattice parameter a and decrease of the cell parameter a of the samples in comparison with that of the undoped sample (Cr0). As for the microstructure and element composition analyses on the surface of the samples produced, SEM and EDS measurements were investigated. According to the measurements, not only were the grain sizes of the samples noted to decrease, but also the surface morphology and grain connectivity were obtained to degrade with increase in the Cr addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Cr addition were also discussed.     

Electrical Properties of Organic–Inorganic Semiconductor Device Based on Rhodamine-101

Rhodamine-101 (Rh101) thin films on n-type Si substrates have been formed by means of evaporation, thus Sn/Rh101/n-Si heterojunctions have been fabricated. The Sn/Rh101/n-Si devices are rectifying. The optical energy gaps have been determined from the absorption spectra in the wavelength range of 400 nm to 700 nm. Rh101 has been characterized by direct optical absorption with an optical edge at 2.05 ± 0.05 eV and by indirect optical absorption with␣an optical edge at 1.80 ± 0.05 eV. It was demonstrated that trap-charge-limited current is the dominant transport mechanism at large forward bias. A␣mobility value of μ = 7.31 × 10⁻⁶ cm² V⁻¹ s⁻¹ for Rh101 has been obtained from the forward-bias current–voltage characteristics.