S. Altin

Effect of Bi deficiency on grain alignment of BiPb-2223 thin film fabricated using rf sputtering process and on critical current density properties

Abstract In the present study, thin films prepared as a function of the Bi concentration in the BiPbSrCaCuO system were synthesised. Thin films were fabricated using radio frequency sputtering method. Crystal structure of the films fabricated was determined from X-ray diffraction measurements. The crystal orientation was analysed by X-ray pole figure and in-plane alignment. Both X-ray diffraction and pole figure analysis revealed that crystallinity in the films decreased significantly with decreasing Bi concentration in the system. A systematic decrease in the superconducting transition temperature and hole concentration per CuO plane was obtained with decreasing Bi concentration. The Jc values of the films were calculated using Bean formula. It exhibits a significant dependence on the magnetic field and temperature. It was found that Jc decreased sharply with increasing applied magnetic field. The highest Jc value was found to be 1·06×106 A cm−2 at 10 K, which corresponded to the best flux pinning among the films fabricated.

Ring-expanded iridium and rhodium N-heterocyclic carbene complexes: a comparative DFT study of heterocycle ring size and metal center diversity

Abstract A new series of ring-expanded six- and seven-membered N-heterocyclic carbene precursors (re-NHCs) and their transition metal complexes were synthesized. The basic properties of the synthesized materials were investigated by density functional theory (DFT). The six- and seven-membered re-NHCs were synthesized in good yield via reaction of the corresponding alkyldibromides or alkyldiiodides with N,N′-bis-(2-phenylbenzene)formamidine in the presence of K2CO3 under aerobic conditions. Complexes, represented by the formula [ML1,2(COD)Cl] (where M = Ir or Rh and L is a ring-expanded N-heterocyclic carbene ligand), were synthesized in the presence of the corresponding free carbene and iridium or rhodium metal precursors in tetrahydrofuran. All new re-NHC complexes were characterized by different analytical techniques, including NMR spectroscopy, X-ray diffraction, UV spectroscopy and elemental analysis. According to molecular electrostatic potential calculations, the electrophilic properties of the complexes were aligned, from highest to lowest, as Ir-6-DiPh, Rh-6-DiPh and Ir-7-DiPh. The HOMO, LUMO and energy gaps of the complexes were calculated by DFT. On the basis of the DFT analysis, it can be predicted that Rh-6-DiPh is the most stable complex and Ir-7-DiPh is more reactive than Ir-6-DiPh.

Enhancement of battery performance of LiMn2O4: correlations between electrochemical and magnetic properties

We report the results of a systematic investigation of structural, electrical transport, magnetic, and electrochemical properties of LiBxMn2−xO4 (where x = 0.0–1), synthesized via a one-step solid state reaction technique. We find that the parent compound (x = 0) has the non-stoichiometric Li1.05Mn2O4 phase and the B ions successfully incorporate the structure for x ≤ 0.5. The resistivity anomaly of the parent compound below 100 K is attributed to the antiferromagnetic correlations. The linear part of the χ−1–T data are used to calculate the effective magnetic moments and to determine the total number of Mn3+ and Mn4+ ions. Magnetization measurements show that Jahn–Teller active Mn3+ ions have high spin configuration. Average valance of Mn ions increases with increasing boron content. Electrochemical studies show improved capacity retention for x = 0.125 for 100 charge–discharge cycles. This improvement is attributed to subtle modifications in the structural and magnetic properties upon substitution.

Effects of SnO on growth and physical properties of BSCCO whiskers

Abstract Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi2Sn1)-223 precursor using suitable heat treatment cycles. Approximately 5 μm thick, 90 μm wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol–1 using Kissinger method based on the differential thermal analysis data. The T c value of the whiskers was found to be 94 K from M–T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M–H) showed that whiskers have paramagnetic–diamagnetic multiphase structure.

The mechanical properties of nanohybrid and bulk fill posterior composites

Objectives: The objective of this work was to investigate the structural properties, thermal conductivity, Differential Thermal Analysis (DTA), Thermo-Gravimetric analysis (TG), surface homogeneity, microhardness, X-ray analysis of nanohybrid and bulk fill composites. Methods: 108 rectangular specimens were prepared from the following composites: (Estelite Sigma Quick (ESQ), Charisma Smart (CS), 3M Espe Filtek Z 250 (EFZ) and Filtek Restorative (FR)) and subjected to various artificial aging protocols (storage in distilled water for 24 h; thermal cycling, 2 × 3000 cycles 5/55°C). The materials were light-cured for 20 s in a 2 mm × 2 mm × 6 mm teflon mould. The nanoparticles of groups were identified by FT-IR spectroscopy. Surface roughness measurements were carried out by optical microscope, the Vickers hardness number was measured with the stainless steel sheet using a micro-indentation tester (Emco Test Durascan), the heat conductivity of the samples was analyzed by the home made thermal conductivity measurement system, thermogravimetric analysis (DTG, 60-AH, Schimadzu) was used to determine the filler mass fraction. Thermogravimetric analysis was performed in argon atmosphere from 30 to 850°C. Results: It was found that the composites have multiphase component such as metallic dopant and organic binder. Conclusions: The XRD investigation showed that there was a broad halo in the pattern which indicates the organic section in the composites. We found that the temperature dependence of the thermal conductivity of the composites depended on the type of the composites, which are low enough for dental applications. The micro-hardness of the samples was analyzed and the result was compared with literature and it was found that the observed results were in agreement with literature.

Electrical and Optical Properties of ZnO‐Fe2O3‐SiO2 Composite Prepared by SOL‐GEL Method

The semiconductor composite was prepared from ZnO, Fe2O3 and SiO2 transition metal oxides by sol‐gel method. The surface morphology of the prepared samples were investigated by scanning electron microscopy (SEM). The activation energies of the samples in the extrinsic and intrinsic regions were found as 0.75 eV and 0.77 eV for ZFS‐1 and 0.22 eV and 0.32eV for ZFS‐2. The value of the optical band gap of the composite samples were calculated from the absorption coefficient depending on photon energy. The optical band gap of the samples were found as 1.60 eV and 1.70 eV for ZFS‐1 and ZFS‐2, respectively.