105 research outputs found

    On Electron Transport in ZrB12, ZrB2 and MgB2

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    We report on measurements of the temperature dependence of resistivity, ρ(T)\rho(T), for single crystal samples of ZrB12_{12}, ZrB2_{2} and polycrystalline samples of MgB2_{2}. It is shown that cluster compound ZrB12_{12} behaves like a simple metal in the normal state, with a typical Bloch -- Gr\"uneisen ρ(T)\rho(T) dependence. However, the resistive Debye temperature, TR=300KT_{R}=300 K, is three times smaller than TDT_{D} obtained from specific heat data. We observe the T2T^{2} term in ρ(T)\rho(T) of these borides, which could be interpreted as an indication of strong electron-electron interaction. Although the ρ(T)\rho (T) dependence of ZrB12_{12} reveals a sharp superconductive transition at Tc=6.0KT_{c}=6.0 K, no superconductivity was observed for single crystal samples of ZrB2_{2} down to 1.3K1.3 K.Comment: 5 pages, 4 figure

    Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2

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    We report on the synthesis and measurements of the temperature dependence of resistivity, R(T), the penetration depth, l(T), and upper critical magnetic field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Gruneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal a superconducting transition at Tc=6.0 K. Although a clear exponential l(T)dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET
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