Annealing Effects on the Structural, Surface, and Superconducting Properties of FeTe 0.55 Se 0.45 Single Crystals
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LETTER
Annealing Effects on the Structural, Surface, and Superconducting Properties of FeTe0.55Se0.45 Single Crystals Liangliang Fan 1 & Pengyu Cheng 1 & Jia Han 1 & Peng Yuan 1 & Wei Sun 1 & Wenlai Lu 1 & Qiling Xiao 1 & Jun-Yi Ge 1 & Jincang Zhang 1 & Fei Chen 1,2 Received: 18 June 2020 / Accepted: 15 October 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this study, we have investigated the annealing effects on FeTe0.55Se0.45 single crystals in S and Te atmospheres. FeTe0.55Se0.45 single crystals were prepared by self-flux method. The as-grown sample shows a rather broad superconducting transition temperature around 6 K and low superconducting volume fraction, which is due to the relatively low proportion of superconducting phase. After being annealed in different vapor atmospheres, their superconducting properties, such as superconducting transition temperature, critical current density Jc, and superconducting volume fraction, could be greatly improved. All experimental results suggest that the bulk superconductivity of FeTe0.55Se0.45 single crystals can be obtained after annealing and thus present another option to remove the excess Fe, which paves the way for further practical application. Keywords Iron selenide . Annealing conditions . Critical current density . FeTe0.55Se0.45 . Raman spectra
1 Introduction In 2008, the new superconductor LaFeAsO1-xFx was discovered by Kamihara’s group [1], which consists of an alternate stacking of blocking and superconducting layers. As the simplest iron-based superconductor, FeSe with anti-PbO structure shows superconducting transition temperature (Tc) around 8 K [2]. Its Tc can be easily tuned by doping, pressure, and so on [3]. For example, optimal Te doping can raise its Tc to 14 K in FeTe0.5Se0.5 [4], and overdoping will suppress its Tc, such as FeTe, exhibiting no superconducting transition at all [5]. Since the Fe (Te, Se) system has high Jc without toxicity, it is suitable for practical applications. However, the existence of excess Fe in Fe (Te, Se) family helps to stabilize its tetragonal phase but suppresses the superconductivity [6].
* Jincang Zhang [email protected] * Fei Chen [email protected] 1
Materials Genome Institute, Department of Physics, Shanghai University, Shanghai 200444, China
2
Shanghai Key Laboratory of High Temperature Superconductors, Shanghai 200444, China
In this way, it is essential to remove the excess Fe. Many methods have been developed, such as soaking the crystal in various liquids [7–9], electrochemical methods [10], and annealing in different atmospheres. Among them, annealing the sample in various atmospheres, such as air, vacuum, oxygen, sulfur, selenium, and tellurium [11, 12], turns out to be the most effective way to remove the excess Fe. To further understand the annealing effect, the impact of many variables should be unveiled, such as annealing time, annealing temperature, sample thickness, and, more importantly, annealing atmosphere. Unveiling the relationship between supercond
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