We report the synthesis and physical properties of a new full Heusler compound, MgPd2Sb, which we found to show superconductivity below Tc = 2.2 K. MgPd2Sb was obtained by a two-step solid state reaction method and its purity and cubic crystal structure (F m-3m, a = 6.4523(1) Å) were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility and heat capacity measurements. The results show that MgPd2Sb is a type-II, weak coupling superconductor (λep = 0.56). The observed pressure dependence of Tc (ΔTc/p ≈ -0.23 K/GPa) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons and electron-phonon coupling in MgPd2Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters to those of all reported Heusler-type superconductors.
New intermetallic compounds Tb 2 Pd 1.25 Ge 2.75 and Dy 2 Pd 1.25 Ge 2.75 have been synthesized using the arc-melting method. The crystallographic structure and magnetic, electronic transport, and thermal properties are reported. The crystal structure obtained from powder x-ray diffraction analysis suggests that these compounds crystallize in the AlB 2 -type structure (space group P6/mmm, no. 191) with lattice parameters a = 4.228 53(5)/4.230 54 (2) Å and c = 3.942 25(9)/3.945 52(5) Å for the compounds with Tb and Dy respectively. The ac and dc magnetic susceptibility studies reveal spin-glass like behavior, with freezing temperature T f = 10.5 K for Tb 2 Pd 1.25 Ge 2.75 and 4.5 K for Dy 2 Pd 1.25 Ge 2.75 . These data are in good agreement with the heat capacity measurements.
Users expect reliable operation of the surge arrester during overvoltages, which may originate from a switching process or a lightning discharge. The necessary conditions to guarantee these expectations are: appropriate construction of the surge arrester, its production being maintained in accordance with technical standards, and a positive results of the type test. The recipient, especially when purchasing large quantities of the product, can check the final quality of the product through selective testing of samples from the market in order to find the best supplier. This manuscript specifies the basic parameters of low-voltage (LV) surge arresters of four manufacturers. Basic electrical parameters, i.e. leakage current and reference voltage before and after the discharge current of 8 µs /20 µs, were determined for 10 randomly selected surge arresters of each manufacturer. Moreover one sample of each varistor batches was aged by 50 simulated lightning strikes. The obtained results of structural analysis indicate that the crystal structure of the varistor materials changes after ageing process, affecting its electrical properties. The proposed research methodology can be employed as a basis for forecasting the stability of the arrester parameters under operating conditions.
The half-Heusler family consists of many semiconducting intermetallic compounds, virtually all of them having a valence electron count (VEC) of 18. We have studied an electrondeficient (VEC = 17) phase MgPdSb and its Pd-stuffed variant MgPd 1.25 Sb. The cubic F4̅ 3m crystal structure was confirmed by the Rietveld refinement of powder X-ray diffraction (XRD) data. The lattice parameter is a = 6.284 and 6.335 Å for MgPdSb and MgPd 1.25 Sb, respectively. The Debye temperature and Sommerfeld coefficient for MgPdSb are Θ D = 282 K and γ = 3.3 mJ mol −1 K −2 , respectively, and are similar to those obtained for MgPd 1.25 Sb. There is neither phase transition nor superconductivity observed above 1.8 K. The differences between the electronic structures of Mg-based half-Heusler compounds make them robustly metallic, irrespective of the electron count and the introduction of interstitial transition metal (Pd) atoms.
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