Ü. Onbaşlı

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.

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

CALCULATION OF MICROWAVE PLASMA OSCILLATIONS IN HIGH TEMPERATURE SUPERCONDUCTORS

It has been determined that the superconducting system, that consists of copper oxide based mercury oxide, behaves as if an oscillating cavity with the plasma frequency of 10 12 Hz under particular amount of magnetic field at space temperature of 100 K. Moreover, plasma frequency of superconducting system (mercury based superconductors) were found to be varying from infrared to microwave region by increasing the temperature from liquid helium of 4.2 K to space temperature of about 100 K. Furthermore, by dealing with calculations of Lawrance-Doniach Model it was found that the plasma frequency versus temperature relation satisfies the sigmoidal distribution whereas the anisotropy factor coincides with the polynomial fitting function.

Structural and dielectric properties of Europium based copper oxide layered perovskite material

ABSTRACT In this study, EuBa2Cu3O7+x (coded as Eu-123) material was synthesized by solid state reaction method and its chemical and physical properties were determined by FTIR, XRF, TGA and DTA techniques. The dielectric and impedance properties of Eu-123 were determined by HP-4194A Impedance Analyzer at room temperature. Eu-123 displays negative dielectric constant (NDC) property, which has a crucial importance for producing metamaterials. Moreover, the relaxation process of the material was also determined as pure conduction. In addition, it was revealed that application of magnetic field does not affect the NDC property of the sample but slightly changes the values of ϵ ′.

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...

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.

Correlation Between The Anisotropy and The Effective Mass of The Quasi‐Particles in Oxide Superconductors

Determination of Josephson penetration depth has a crucial importance in calculation of both anisotropy factor and the effective mass of quasi‐particles (m*) in high temperature copper oxide superconductors. In this study, the effective mass values of the quasi‐particles have been determined via third derivative of phase differences of quantum wave function that represents the superconducting state of the system. According to our calculations, the anisotropy factor and m* have been affected by temperature varying from 5 to 90 K for over‐doped sample. Moreover, the anisotropy factor and m* of the superconducting media are found to be changed by temperature, applied magnetic field and the oxygen annealing procedures. Furthermore, the quantum vertex which corresponds to the quantum gravity that has been already determined for optimally oxygen doped mercury cuprate superconductors has not showed up in over‐doped samples investigated.