Structural disorder in Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 superconductors studied by M\"ossbauer spectroscopy

TL;DR

This study uses Mössbauer spectroscopy to analyze the magnetic and structural properties of Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 superconductors, revealing the effects of annealing and intercalation on their superconducting behavior.

Contribution

It provides detailed insights into the magnetic phases and vacancy ordering in iron-chalcogenide superconductors using Mössbauer spectroscopy, highlighting how annealing influences their superconducting properties.

Findings

Superconductivity at 40 K and 25 K observed after annealing.

Annealing removes iron vacancies and promotes vacancy ordering.

Presence of magnetically ordered iron in Fe-Se sheets and interstitial regions.

Abstract

Two iron-chalcogenide superconductors Li(x)[C5H5N](y)Fe(2-z)Se2 and Cs(x)Fe(2-z)Se2 in the as-prepared and annealed state have been investigated by means of the Moessbauer spectroscopy versus temperature. Multi-component spectra are obtained. One can see a non-magnetic component due to iron located in the unperturbed Fe-Se sheets responsible for superconductivity. Remaining components are magnetically ordered even at room temperature. There is some magnetically ordered iron in Fe-Se sheets perturbed by presence of the iron vacancies. Additionally, one can see iron dispersed between sheets in the form of magnetically ordered high spin trivalent ions, some clusters of above ions, and in the case of pyridine intercalated compound in the form of alpha-Fe precipitates. Pyridine intercalated sample shows traces of superconductivity in the as-prepared state, while cesium intercalated sample in the as-prepared state does not show any superconductivity. Superconductors with transition temperatures being 40 K and 25 K, respectively, are obtained upon annealing. Annealing leads to removal/ordering of the iron vacancies within Fe-Se sheets, while clusters of alpha-Fe grow in the pyridine intercalated sample.