Jenny Darja Vinko

Possibility of high temperature superconducting phases in PdH

Possible new superconducting phases with a high critical transition temperature (Tc) have been found in stable palladium–hydrogen (PdHx) samples for stoichiometric ratio x=H/Pd⩾1, in addition to the well-known low critical transition temperature (0⩽Tc⩽9) when x is in the range (0.75⩽x⩽1.00). Possible new measured superconducting phases with critical temperature in the range 51⩽Tc⩽295 K occur. This Tc varies considerably with every milli part of x when x exceeds unit. A superconducting critical current density Jc⩾6.1×104 A cm−2 has been measured at 77 K with HDC=0 T.

Magnetic and transport properties of PdH: Intriguing superconductive observations

Since the discovery of superconductivity in palladium-hydrogen (PdH) and its isotopes (D,T) at low temperature, several efforts have been made to study the properties of this system. Superconductivity of PdH system has been initially claimed by resistance drop versus temperature and then confi rmed by dc magnetic susceptibility measurements. These studies have shown that the critical transition temperature is a function of the hydrogen concentration x in the PdHx system. In all these experiments, the highest concentration x of hydrogen in palladium was lower than the unit. In the last decade we defi ned a room temperature and room pressure technique to load hydrogen and its isotopes into palladium at levels higher than unit, using electrochemical set-up, followed by a stabilization process to maintain the hydrogen concentration in palladium lattice stable. In the meanwhile, several measurements of resistance versus temperature have been performed. These measurements have shown several resistive drops in the range of [18K<Tc< 273K] similar to the results presented in literature, when the superconducting phase has been discovered. Moreover, on PdH wires 6cm long the current-voltage characteristic with a current density greater than 6*104 Acm-2 has been measured at liquid nitrogen temperature. These measurements have the same behavior as superconducting I-V characteristic with sample resistivity, at 77K, of two orders of magnitude lower than copper or silver at the same temperature. The measurements of fi rst and third harmonic of ac magnetic susceptibility in PdHx system have been performed. These represent a good tool to understand the vortex dynamics, since the superconducting response is strongly non-linear. Clear ac susceptibility signals confi rming the literature data at low temperature (9K) and new signifi cant signals at high temperature (263K) have been detected. A phenomenological approach to describe the resistance behaviour of PdH versus stoichiometry x at room temperature has been developed. The value x=1.6 to achieve a macroscopic superconducting state in PdHx has been predicted.

A REVIEW OF HIGH TEMPERATURE SUPERCONDUCTING PROPERTY OF PDH SYSTEM

The discovery of superconductivity in palladium-hydrogen (PdH) and its isotopes (D,T) at low temperature, brought about extensive study of this system. These studies have shown that the critical transition temperature is a function of the H concentration x in the PdHx system with Tc=9K for x=1. In the last decade we defined a room temperature and room pressure technique to load H and maintain stable the stoichiometry in Pd lattice at levels higher than unit. Several magnetic and electric transport measurements have been performed showing transition temperature in the range of [18K< Tc < 273K]. Moreover in a typical critical current measurement configuration, current density greater than 6*104Acm-2⊐ has been measured at liquid nitrogen temperature. The 263.5K superconducting transition after a week of sample storage at room pressure and temperature, decreased down to 261.5K and after 2 years it became 160.5K, demonstrating a fairly good stability of the sample. Evidences of the flux exclusion (ZFC measurements) and the flux expulsion (FC measurements) have been found at very high transition temperature (Tc=235K) for the PdH system.

PICO-CHEMISTRY: THE POSSIBILITY OF NEW PHASES IN SOME HYDROGEN/METAL SYSTEMS

In the standard model, matter is an assembly of quarks that combine under the action of the strong nuclear force to give nucleons (protons and neutrons), further giving atom nuclei that under the action of the electromagnetic force combine with electrons to render atoms and molecules. Each of these interactions has a well defined range of binding energies. A novel type of purely electromagnetic interaction is proposed, with binding energies and dimensions between chemistry and nuclear. This type of binding could result in completely novel materials (super-conductivity) and potential energy production.

Flux Dynamic Changes by Neutron Irradiation in BISCCO: High Harmonics AC Susceptibility Analysis

High harmonics ac susceptibility measurements joint with neutron irradiations on quasi-bi-dimensional high temperature superconductor (quasi-2D-HTSC) are good tools to study the flux dynamics and its interaction with pinning processes in these superconductors. Flux neutron intensity of shows a deep change in the flux pinning dynamics in Bi-Sr-Ca-Cu-O (BSCCO) system. Third harmonic susceptibility signal increases in amplitude after the neutron irradiation, followed by a rise of the pinning and critical current. Moreover, after the irradiation, the measurements underline the demise of the anomalous peak effect (PE) associated with a three-dimensional/two-dimensional (3D/2D) flux lattice transition.

Glass-collective pinning and flux creep dynamics regimes in MgB/sub 2/ bulk

Superconducting dynamic response in zero field cooling (ZFC) of MgB/sub 2/ bulk has been analyzed using high harmonic ac susceptibility measurements (/spl chi//sub n/). The driving external ac magnetic field is in the frequency range [107Hz<f<2070Hz], the driving external dc magnetic field is in the range [0T<H/sub dc/<5T] and the temperature has been varied in the range [15K<T<38K]. These responses are characterized from the critical states that decay in glass states via creep processes. In this analysis different frequency values at fixed H/sub dc/ investigate different current levels. This way, different pinning regimes as single vortex, small bundle, large bundle are studied. Using this approach some parts of the MgB/sub 2/ three-dimensional phase diagram H-T-J can be described.

Increasing of superconducting pinning potential Up and critical current Jc due to the hydrogen loading in sintered YBCO

Abstract YBCO sintered samples have been hydrogenated using chemical absorption. Experimental measurements of the ac higher harmonic susceptibility versus frequency of applied magnetic field have been performed. Increasing of pinning potential U p and critical current J c due to the adsorbed hydrogen has been found. An increasing of 5% in J c and U p has been quantitatively measured using the non-linear magnetic diffusion equation.

Towards a physical lattice model for the atom and implications for high-Tc superconductivity

Starting from Cook’s model [D. N. Cook, Models of the Atomic Nucleus (Springer, Berlin, 2006)], we proposed a non-Archimedean approach to show that we can transform his purely mathematical model into a physical one. In the first stage, we kept the f.c.c. lattice model surrounded by a vapor phase from which we can only extract “symmetric” entities (quantons?) which are the electrons. This in our opinion gives a much better global view of what the atom could be. When assembling the nuclei into a lattice, there is reciprocal influence between the vapor phase and the lattice. Consequently, superconductivity occurs when temperature decrease brings to freezing the vapor phase and when the “crystallization” of the vapor phase gives some symmetric tiling of the volume around the lattice, thanks to Curie’s theorem. Looking for high temperature superconductivity therefore is equivalent to finding symmetric crystallization of the vapor phase. In that sense this pleads for the use of heterogeneous materials in the “c...