The Effect of Ag Addition on the Superconducting Properties of FeSe0.94

Abstract

The tetragonal FeSe phase is an intensively investigated iron based superconductor. In this study we examined the influence of Ag addition on the superconducting properties of selenium deficient polycrystalline FeSe 0.94 . The samples were obtained by solid state reaction and melting methods. XRD analysis shows the presence of tetragonal phase and EDX analysis establishes inhomogeneous Ag distribution in the grains. The superconducting properties were investigated by fundamental and third harmonic AC magnetic susceptibility. The intergranular critical current determined from AC magnetic susceptibility in the Ag doped sample is several times higher than that in the undoped one, obtained by melting at approximately the same temperatures. Intragranular current is field independent up to almost 1000 Oe. Using the temperature dependence of third harmonic AC magnetic susceptibility at different DC magnetic fields, the irreversibility lines were obtained for all samples. It is found that Ag addition increased the irreversibility field in comparison with undoped melted and powder sintered samples. All results show that the Ag addition in selenium deficient (FeSe 0.94 ) samples leads to improvement of inter-and intra-granular properties: screening ability, pinning, activation energy and critical current and improves the irreversibility line.

The effect of the sintering process on Ag–added FeSe0.94 superconducting wire

“…In figure 1(a), the XRD patterns displayed are of the Ag-added FeSe 0.94 for wires 1, 2, 3 and include the data of the precursor for comparison. It can be observed that most of the reflection peaks are well indexed to the tetragonal crystal structure with space group P4/nmm for the precursor, and all wires are in agreement within earlier reports [24,25]. However, in the precursor and wire 3, an additional reflection peak appeared at about 2θ = 31 • , which belongs to the δ-FeSe phase with space group P6 3 /mmc.…”

“…Metal additives are one of the techniques used to overcome these challenges for both conventional and nonconventional superconductors. The introduction of silver into Fe(Se, Te) superconducting polycrystalline has been proven to improve its structural and superconducting properties [24][25][26][27][28][29][30][31]. It was reported that silver develops intra-and intergrain connectivity and enhances the critical parameters like the superconducting transition temperature (T c ), current density (J c ), upper critical field (H c2 ), irreversibility field (H irr ) and the screening ability, pinning, activation energy and chemical phase stability.…”

Mixed state properties analysis in AC magnetic field of strong pinning Fe(Se,Te) single crystal

“…where T * is the temperature where the investigated phenomenon is no more detectable. Thanks to the fitting procedure, it can be noted that the H irr values for T = 4 K, which is typically considered for power applications of superconductivity, are in the range of about 30 ÷ 40 Tesla in agreement with the ones present in literature for 11 family samples [9,[78][79][80][81] and other sample types [82][83][84][85][86]. In particular, the H irr value at T = 4 K for ν = 9693 Hz is equal to 42 Tesla which approaches the maximum value reported by Hosono et al [9].…”

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

“…Moreover, a small amount of Ag was found to enter into the crystal structure of FeSe 0.5 Te 0.5 . We established that the Ag addition in FeSe 0.94 improves both the intra-and inter-granular superconducting properties and slightly increases the irreversibility field [7]. Further investigations showed [8] that critical temperature, the magnetoresistance, the upper critical field and the activation energy for thermally activated flux flow also increased as a result of 4 wt % Ag doping.…”