Carrier Transport in Magnesium Diboride: Role of Nano-inclusions

Anisotropic-gap and two-band effects smear out the superconducting transition (Tc) in literature reported thermal conductivity of MgB2, where large electronic contributions also suppress anomaly-manifestation in their negligible phononic-parts. Present thermal transport results on scarcely explored specimens featuring nano-inclusions exhibit a small but clear Tc-signature, traced to relatively appreciable phononic conduction, and its dominant electronic-scattering. The self-formed MgO as extended defects strongly scatter the charge carriers and minutely the phonons with their longer-mean-free-path near Tc. Conversely, near room temperature, the shorter-dominant-wavelength phonon's transport is hugely affected by these nanoparticles, undergoing ballistic to diffusive crossover and eventually entering the Ioffe-Regel mobility threshold regime.Comment: 14 pages, 4 figures, 28 reference

Shielding and Trapped Field Properties of Large MgB2 Bulk

AbstractWe have studied the magnetic shielding properties of MgB2 bulk fabricated by a reactive liquid Mg infiltration (Mg-RLI) method. The magnetic shielding profiles indicated partially field-penetrated areas at the bulk periphery with weaker pinning force at 38K. We discuss about the superconductive inhomogeneity in the bulk by comparing the shielding profiles with trapped field ones by the subsequent zero-field-cooled magnetization (ZFCM) and the pulsed-field magnetization (PFM). The present method is advantageous to detect the inhomogeneity at the periphery of a large superconducting bulk

Frequency dependence of the microwave surface resistance of MgB2 by coaxial cavity resonator

We report on the microwave (mw) properties of a cylindrical MgB2 rod prepared by the reactive liquid Mg infiltration technology. The MgB2 rod, 94.3 mm long, is used as inner conductor of a coaxial cavity having a Cu tube as external conductor. By analyzing the resonance curves of the cavity in the different resonant modes and at different temperatures, we have determined the temperature dependence of the mw surface resistance, Rs, of the MgB2 material, at fixed frequencies, and the frequency dependence of Rs, at fixed temperatures. Our results show that the Rs(f) curves follow a f^n law, where n decreases on increasing the temperature, starting from n=2, at T=4.2 K, down to n=0.7 at T>Tc. The double gap nature of MgB2 manifests itself in the presence of a wide low-T tail in the R(T) curves, which can be ascribed to the quasiparticles thermally excited through the pi gap even at relatively low temperatures

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

We report on the microwave properties of coaxial cavities built by using bulk MgB2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity by using an outer MgB2 cylinder and an inner MgB2 rod and a hybrid cavity by using an outer copper cylinder and the same MgB2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance Rs of the MgB2 materials as a function of the temperature and the frequency, in the absence of dc magnetic fields. At T=4.2 K and f ≈ 2.5 GHz, by an mw pulsed technique, we have determined the quality factor of the homogeneous cavity as a function of the input power up to a maximum level of about 40 dBm (corresponding to a maximum peak magnetic field of about 100 Oe). Contrary to what occurs in many films, Rs of the MgB2 material used does not exhibit visible variations up to an input power level of about 10 dBm and varies less than a factor of 2 on further increasing the input power of 30 dB

High Force Magnetic Levitation Using Magnetized Superconducting Bulks as a Field Source for Bearing Applications

n/

Structural and Thermodiffractometric Studies of Coordination Polymers Containing Ditopic Exobidentate Nitrogen Ligand

nul

Synthesis of alkaline-earth hexaborides, MB6 (M = Ca, Ba, Sr), by a solid state metathesis (SSM) reaction

A new synthetic pathway for alkaline-earth hexaborides has been developed. This method involves a solid state metathesis between an alkaline-earth (Ca, Ba, Sr) salt and MgB2, which can be performed at relatively low temperatures, without any catalyst and with no hazardous side products. The proposed protocol shows a good reproducibility and a much lower energy consumption (and, consequently, lower costs) than any known traditional synthesis. In view of the possibility of using alkaline-earth hexaborides as overdopants in MgB2 superconductors in order to enhance its transport properties in magnetic field, several MgB2 + MB6 bulk composites were obtained with the \u201cReactive Liquid Mg Infiltration\u201d (Mg-RLI) technique, and characterized by X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM) methods

Crystal and molecular structures of the organometallic species [Rh2(bim)2(cod)2]Cl2 \ub72H2O [bim=bis-(1-imidazolyl)methane; cod =1,5-cyclooctadiene]

The synthesis and X-ray powder diffraction data for the organometallic [Rh2(bim)2(cod)2]Cl2\ub72H2O species are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. [Rh2(bim)2(cod)2]Cl2\ub72H2O was found to crystallize in the orthorhombic Cmca space group. The lattice parameters were determined to be a =21.3574(6), b=10.7764(3), c=14.2795(4) \uc5, V=3286.5(2) \uc53, for Z=4. The crystal structure was found to contain dimeric [Rh2(bim)2(cod)2]2+ cations, in which the bim ligands bridge Rh(cod) fragments with an intermetallic separation of ca. 8.90 \uc5. The crystal structure is completed by chloride ions and hydrogen-bonded water molecules, situated in the small cavities of the large cation substructure. The conformation of the bim ligand, lying on a crystallographic mirror plane, is rigorously Cs