Superconductivity in metal rich Li-Pd-B ternary Boride

8K superconductivity was observed in the metal rich Li-Pd-B ternary system. Structural, microstructural, electrical and magnetic investigations for various compositions proved that Li2Pd3B compound, which has a cubic structure composed of distorted Pd6B octahedrons, is responsible for the superconductivity. This is the first observation of superconductivity in metal rich ternary borides containing alkaline metal and Pd as a late transition metal. The compound prepared by arc melting has high density, is stable in the air and has an upper critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur

X-ray and Radio Follow-up Observations of High-Redshift Blazar Candidates in the Fermi-LAT Unassociated Source Population

We report on the results of X-ray and radio follow-up observations of two GeV gamma-ray sources 2FGL J0923.5+1508 and 2FGL J1502.1+5548, selected as candidates for high-redshift blazars from unassociated sources in the {\it Fermi} Large Area Telescope Second Source Catalog. We utilize the Suzaku satellite and the VLBI Exploration of Radio Astrometry (VERA) telescopes for X-ray and radio observations, respectively. For 2FGL J0923.5+1508, a possible radio counterpart NVSS J092357+150518 is found at 1.4 GHz from an existing catalog, but we do not detect any X-ray emission from it and derive a flux upper limit $F_{\rm 2-8 keV} <$ 1.37 $\times$ 10$^{-14}$ erg cm$^{-2}$ s$^{-1}$. Radio observations at 6.7 GHz also result in an upper limit of $S_{\rm 6.7 GHz}$ $<$ 19 mJy, implying a steep radio spectrum that is not expected for a blazar. On the other hand, we detect X-rays from NVSS J150229+555204, the potential 1.4 GHz radio counterpart of 2FGL J1502.1+5548. The X-ray spectrum can be fitted with an absorbed power-law model with a photon index $\gamma$=1.8$^{+0.3}_{-0.2}$ and the unabsorbed flux is $F_{\rm 2-8 keV}$=4.3$^{+1.1}_{-1.0}$ $\times$ 10$^{-14}$ erg cm$^{-2}$ s$^{-1}$. Moreover, we detect unresolved radio emission at 6.7 GHz with flux $S_{\rm 6.7 GHz}$=30.1 mJy, indicating a compact, flat-spectrum radio source. If NVSS J150229+555204 is indeed associated with 2FGL J1502.1+5548, we find that its multiwavelength spectrum is consistent with a blazar at redshift $z \sim 3-4$.Comment: 24 pages, 7 figures, 6 tables, accepted for publication in Ap

Lithium colloids and color center creation in electron-irradiated Li2NH observed by electron-spin resonance

4 pagesInternational audienceWe have irradiated Li2NH powder with MeV electrons at room temperature and investigated the introduced defects with electron spin resonance. CESR indicates the presence of nanosize metallic Li colloids seen as a Lorentzian line with a g = 2.0023 and a line width DeltaH = 50 microT. A second, broader, signal (DeltaH = 3 to 4 mT) appears superimposed upon the Li line at low T (Curie-type behavior) which exhibits complex T-dependence with a break near 180 K for its g-value and DeltaH. We are suggesting for the latter a vacancy-type defect in the NH-sublattice, with freezing of its H-component below 180 K. When heated both the Li colloids and the color centers anneal around 100 C probably due to hydrogen evolution and subsequent chemical degradation

Dehydriding and rehydriding reactions of LiBH₄

Structural differences in LiBH₄ before and after the melting reaction at approximately 550 K were investigated to clarify the experimental method for the confirmation of reversible dehydriding and rehydriding reactions. Since the long-range order of LiBH₄ begins to disappear after the melting reaction was achieved, investigation of the atomistic vibrations of the [BH₄]-anion in LiBH₄ was found to be effective for the confirmation of the reversibility. In the present study, LiBH₄ was successively dehydrided (decomposed) into LiH and B under 1 MPa of hydrogen at 873 K, and then rehydrided (recombined) into LiBH₄ under 35 MPa of hydrogen at the same temperature (873 K). The temperatures at the beginning and ending of the dehydriding reaction are lowered, by approximately 30 K, for LiBH₄ substituted (or mixed) with Mg (atomic ratio of Li:Mg=9:1) as compared to those for LiBH₄ alone. This is similar to the tendency exhibited by LiNH₂

Magnetization measurements on Li2Pd3B superconductor

Magnetization in DC magnetic fields and at different temperatures have been measured on the Li2Pd3B compound. This material was recently found to show superconductivity at 7-8K. Critical fields Hc1(0) and Hc2(0) have been determined to be 135Oe and 4T, respectively. Critical current density, scaling of the pinning force within the Kramer model and the irreversibility field data are presented. Several superconductivity parameters were deduced: x(csi)=9.1 nm, l(lamda)=194nm and k=21. The material resembles other boride superconductors from the investigated points of view.Comment: 10 pages, 5 figure

First-principles study on the intermediate compounds of LiBH4_4

We report the results of the first-principles calculation on the intermediate compounds of LiBH$_4$. The stability of LiB$_3$H$_8$ and Li$_2$B$_n$H$_n (n=5-12)$ has been examined with the ultrasoft pseudopotential method based on the density functional theory. Theoretical prediction has suggested that monoclinic Li$_2$B$_{12}$H$_{12}$ is the most stable among the candidate materials. We propose the following hydriding/dehydriding process of LiBH$_4$ via this intermediate compound : LiBH$_4 \leftrightarrow {1/12}$Li$_{2}$B$_{12}$H$_{12} + {5/6}$ LiH $+ {13/12}$H$_2 \leftrightarrow$LiH $+$ B $+ {3/2}$H$_2$. The hydrogen content and enthalpy of the first reaction are estimated to be 10 mass% and 56 kJ/mol H$_2$, respectively, and those of the second reaction are 4 mass% and 125 kJ/mol H$_2$. They are in good agreement with experimental results of the thermal desorption spectra of LiBH$_4$. Our calculation has predicted that the bending modes for the $\Gamma$-phonon frequencies of monoclinic Li$_2$B$_{12}$H$_{12}$ are lower than that of LiBH$_4$, while stretching modes are higher. These results are very useful for the experimental search and identification of possible intermediate compounds.Comment: 7 pages, 5 figures, submitted to PR