Z. Güven Özdemir

The chaotic points and XRD analysis of Hg-based superconductors

In this article, high Tc mercury based cuprate superconductors with different oxygen doping rates have been examined by means of magnetic susceptibility (magnetization) versus temperature data and X-ray diffraction pattern analysis. The under, optimally and over oxygen doping procedures have been defined from the magnetic susceptibility versus temperature data of the superconducting sample by extracting the Meissner critical transition temperature, Tc and the paramagnetic Meissner temperature, TPME, so called as the critical quantum chaos points. Moreover, the optimally oxygen doped samples have been investigated under both a.c. and d.c. magnetic fields. The related a.c. data for virgin(uncut) and cut samples with optimal doping have been obtained under a.c. magnetic field of 1 Gauss. For the cut sample with the rectangular shape, the chaotic points have been found to occur at 122 and 140 K, respectively. The Meissner critical temperature of 140 K is the new world record for the high temperature oxide superconductors under normal atmospheric pressure. Moreover, the crystallographic lattice parameters of superconducting samples have a crucial importance in calculating Josephson penetration depth determined by the XRD patterns. From the XRD data obtained for under and optimally doped samples, the crystal symmetries have been found in tetragonal structure.

The Effect of Different Liquid Crystal Compounds on Conduction Mechanism of 4-Cyano-4′-n-heptybiphenyl (7CB) by Using I-V Characteristics

We have investigated the current-voltage characteristics of 7CB (4-cyano-4′-n-heptybiphenyl), 7CB:LC1 (5-(10-undecenyloxy)-2-[[[4-hexylphenyl]imino]methl]phenol) and 7CB:LC2 (5-(10-undecenyloxy)-2-[[[4-hexyloxyphenyl]imino]methl]phenol) by means of negative differential resistance and conductivity mechanism. According to differential resistance calculations, only 7CB and 7CB:LC1 exhibit N-shaped voltage-controlled NDR effect. The electrical conductivity mechanism of the related LCs has been investigated by natural logarithmic current-voltage curves. The nonlinear property of I-V characteristics has been explained by space charge limited conduction mechanism for 7CB:LC2.

Some Contemporary and Prospective Applications of High Temperature Superconductors

High temperature superconductors (HTS) have a wide range of very sensitive and reliable advanced technological applications. In this chapter, some examples of contemporary and prospective usage of the superconductors such as in vivo living body measurements in medicine, terahertz equipments for security systems, quantum bit namely “qubit” applications in quantum computation and bolometers for some space investigations will be dealt with. Especially in medicine, superconductors have been reliably utilized in Magnetic Resonance Imaging (MRI), Magnetic Resonance Spectroscopy (MRS), magnetoencephalography (MEG) and magnetocardiography (MCG) for both analysis of magnetic activity of different regions of the human body such as brain and heart’s wave activities and very early diagnosis of several diseases. All equipments mentioned above contain Superconducting Quantum Interference Device (SQUID), which is based on the Josephson Effect. SQUID is a very sensitive magnetic detector to determine the change of the magnetic flux in material media of the order of 10-15 T兼態, which coincides with the order of magnetic flux quanta, Φ待 = に.どはばぱ捲など貸怠泰 劇兼態. The sensitivity of SQUID is revealed easily by remembering the fact that the magnetic field of the Earth equals to 5x10-5 Tesla. Besides these contemporary applications in medicine mentioned above, the Proton-MRS (PMRS) measurements will be proposed for forensic science investigations as one of the prospective implementations of HTS’s. Because of the fact that some in vivo investigations via P-MRS provide the facility to detect the minor changes of metabolites in human brain (Onbasli et al., 1999), the method, which enables to detect the mild head injuries, which cannot be recognized according to Glasgow Coma Scale (GCS) (Teasdale & Jennett, 1974) from the neurological point of view, will be presented in this chapter. Moreover, one of the remarkable features of HTS is that some oxide layered HTS work as a terahertz wave source. From this point of view, HTS‘s are also utilized in security systems, in remote sensing and non-destructive diagnosis. As was previously determined that the

Polyvinyl Alcohol/EuBa2Ca2Cu3O9−x Composites: Dielectric and Mechanical Properties

In the present work, the influence of EuBa2Ca2Cu3O9−x (coded as Eu-1223) ceramic additive on the mechanical and dielectric properties of poly(vinyl alcohol) (PVA) polymer were investigated for the first time. PVA/Eu-1223 polymer-ceramic thick film composites were prepared by solution casting method with different ceramic contents varying from 1 to 5%. The surface morphology of the samples were studied with scanning electron microscope revealed that adding higher concentration of Eu-1223 increases the roughness of the surface as well as the fragility of the PVA. Thermogravimetric analyses results revealed that the increasing Eu-1223 additive enhances slightly both the thermal and oxidative stability of the PVA. Furthermore, FTIR analysis of the composite displayed new FTIR transmittance peaks that can be attributed to the formation of a reaction between the PVA polymer chain and the ceramic additive. The mechanical properties in the context of stress–strain curves of the samples unveiled that increasing ceramic doping improves the Young’s modulus of PVA films. The impedance and dielectric properties of the samples recorded at room temperature indicated a space charge polarization regardless of the doping concentration. The complex electrical modulus analysis also pointed out a pure conduction process. The Nyquist and phase angle plots defined the grain and grain boundary properties along with the ideal capacitor ability of the composites. Especially, the lower ε′ and ε″ values were achieved for the 5% Eu-1223 additive level concentration. This work brings out that 5% Eu-1223 added PVA thick film may be suggested as a low dielectric loss dielectric material for supercapacitor applications.

The influence of oxygen doping on critical parameters of mercury based superconductors

In this work, the effect of oxygen doping on the critical parameters of the mercury based superconducting sample such as critical transition temperature, Tc, critical magnetic field, Hc, critical current density, Jc, has been investigated by the magnetic susceptibility versus temperature (χ-T) and magnetization versus applied magnetic field (M-H) measurements and, X-Ray Diffraction (XRD) patterns. It has been observed that regardless of the oxygen doping concentration, the mercury cuprate system possesses two intrinsic superconducting phases together, HgBa2Ca2Cu3O8+x and HgBa2CaCu2O6+x. However, the highest Tc has been determined for the optimum oxygen doped sample. Moreover, it has been revealed that superconducting properties, crystal lattice parameters, coherent lengths, ξab, ξc and the anisotropy factor γ etc. are very sensitive to oxygen doping procedures. Hence, the results presented this work enables one to obtain the mercury based superconductor with the most desirable criticals and other paramete...

Determination of Chaotic Behavior in Liquid Crystal

In this work, chaotic behavior of 4′-(3,7-dimethyloctyloxy)-4-biphenylcarboxylic acid liquid crystal (LC) has been investigated by Schwarzian derivative method. Determination of negative Schwarzian derivative constitutes a sufficient condition for specifying chaotic behaviors mathematically in nonlinear systems. For this purpose, temperature variation of heat flow experimental data of LC has been utilized. In this context, the chaotic behavior of the LC compound has been investigated by means of the Schwarzian derivative. The chaotic behavior on the transition has been mathematically proved for both heating and cooling procedure.

Dielectric Properties of 4-Cyano-4′-pentylbiphenyl (5CB): 4-[4-(S)-2-Methylbutoxybenzoyloxy]benzoic Acid (BAC) Composite

Dielectric relaxation dynamics properties of 5CB (4-cyano-4′-pentylbiphenyl) and BAC(4-[4-(S)-2-methylbutoxybenzoyloxy]benzoic acid) have been investigated. In this respect, dielectric properties of 5CB plus (1%)BAC have been compared with 5CB. The polarizing microscopy results show that BAC and 5CB exhibit enantiotropic N* mesophase and N mesophase, respectively. The real (ϵ ′) and imaginary components (ϵ′′) of dielectric constant have been calculated by capacitance method. The dielectric relaxation mechanisms of liquid crystals have been analyzed by Cole-Cole plots and the Debye distribution parameters (α) have been calculated. It has been also determined that adding BAC to 5CB increases the voltage dependent dielectric strength.

Dielectric Anisotropy Properties of BAC-Doped 5CB Liquid Crystal

Dielectric anisotropy properties and splay elastic constant, K11 for 5CB (4-cyano-4’-pentylbiphenyl) plus 1% BAC(4-[4-(S)-2-methylbutoxybenzoyloxy]benzoic acid] have been investigated. The frequency dependent dielectric anisotropy and splay elastic constant have been calculated by using capacitance-voltage curves for various frequencies. The critical frequency, fc values of dielectric anisotropy for 4-cyano-4′-pentylbiphenyl (5CB) and 5CB+(1%)BAC composites were found to be 433.5 kHz and 439.5 kHz, respectively. It has been determined that BAC doping to 5CB decreases both threshold voltages and splay elastic constants for all frequencies applied. The decrease in K11 values has been interpreted as the decrease of distortion in the system.

Impedance and dielectric properties of mercury cuprate at nonsuperconducting state

In this paper, impedance and dielectric properties of nonsuperconducting state of the mercury-based cuprate have been investigated by impedance measurements within the frequency interval of 10 Hz–10 MHz for the first time. The dielectric loss factor (tgδ) and ac conductivity (σac) parameters have also been calculated for non-superconducting state. According to impedance spectroscopy analysis, the equivalent circuit of the mercury cuprate system manifests itself as a semicircle in the Nyquist plot that corresponds to parallel connected resistance–capacitance circuit. The oscillation frequency of the circuit has been determined as approximately 45 kHz which coincides with the low frequency radio waves. Moreover, it has been revealed that the mercury-based cuprate investigated has high dielectric constants and hence it may be utilized in microelectronic industry such as capacitors, memory devices etc., at room temperature. In addition, negative capacitance (NC) effect has been observed for the mercury cuprate regardless of the operating temperatures at nonsuperconducting state. Referring to dispersions in dielectric properties, the main contribution to dielectric response of the system has been suggested as dipolar and interfacial polarization mechanisms.