A Solution for Solution-Produced
β‑FeSe:
Elucidating and Overcoming Factors that Prevent Superconductivity
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Abstract
A new
low-temperature solvothermal synthesis of superconducting
β-FeSe has been developed using elemental iron and selenium
as starting materials. We have shown that syntheses performed in aerobic
conditions resulted in the formation of nonsuperconducting antiferromagnetic
β-FeSe, whereas syntheses performed in ultra-dry and oxygen-free
conditions produced superconducting β-FeSe. Detailed characterization
of both types of samples with magnetometry, resistivity, Mössbauer
spectroscopy, synchrotron X-ray and neutron powder diffraction, and
pair-distribution function analysis uncovered factors that trigger
the loss of superconductivity in β-FeSe. Vacancies in the iron
sublattice and the incorporation of disordered oxygen-containing species
are typical for nonsuperconducting antiferromagnetic samples, whereas
a pristine structure is required to preserve superconductivity. Exposure
to ambient atmosphere resulted in the conversion of superconducting
samples to antiferromagnetic ones. This synthetic method creates new
possibilities for soft chemistry approaches to the synthesis and modification
of iron-based superconductors