Improvement of the superconducting properties of polycrystalline FeSe by silver addition

TL;DR

Adding silver to polycrystalline FeSe improves its superconducting properties by enhancing critical temperature, upper critical field, and flux pinning, making polycrystalline samples comparable to single crystals.

Contribution

This study demonstrates that silver addition in FeSe enhances superconducting properties and provides insights into the mechanisms involved.

Findings

Ag improves intergrain connectivity and reduces transition width.

Ag increases Tc, Bc2, and magnetoresistance.

Impurity phases like Ag2Se may contribute to flux pinning.

Abstract

We investigated the influence of different Ag additions (up to 10 wt %) on the superconducting properties of FeSe0.94. The structural investigations (XRD and SEM) indicated that Ag is present in three different forms. Ag at grain boundaries supports the excellent intergrain connections and reduces superconducting transition width to values smaller than 1K at B=0 and smaller than 2.74 K at B=14 T. Ag insertion in the crystal lattice unit cell provides additional carriers and changes the electron hole imbalance in FeSe0.94. This results in an increase in the magnetoresistive effect (MR) and critical temperature (Tc). Reacted Ag forms a small amount (~1%) of Ag2Se impurity phase, which may increase the pinning energy in comparison with that of the undoped sample. The enhanced upper critical field (Bc2) is also a result of the increased impurity scattering. Thus, unlike cuprates Ag addition enhances the Tc, Bc2, pinning energy and MR making the properties of polycrystalline FeSe0.94 similar to those of single crystals.