Microstructure and phase transformations in FeSe superconductor

Diko, P.; Antal, V.; Kavečanský, V.; Yang, C-H.; Chen, I.

doi:10.1016/j.physc.2012.01.018

Cited by 22 publications

(11 citation statements)

References 10 publications

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“…The XRD analyses show that besides the presence of large amount of tetragonal phase in melt growth FeSeAg0 a small amount non superconducting hexagonal phase is also detected (Fig.1). This is in agreement with a previous study of FeSe phase diagram [9] where it is shown that hexagonal δ(Fe 1+x Se) phase (with Ni-As structure) crystallize from the melt and subsequently is transformed to the tetragonal (Fe 1+x Se) (with PbO structure). However, some residual high temperature phase is always present in the prepared samples.…”

Section: Resultssupporting

confidence: 93%

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

Nazarova

Balchev

Nenkov

et al. 2015

Supercond. Sci. Technol.

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We investigated the influence of different Ag additions (up to 10 wt %) on the superconducting properties of FeSe 0.94 . 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 ΔT to values smaller than 1K at B=0 and ΔT ≤ 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 FeSe 0.94 . This results in an increase in the magnetoresistive effect (MR) and critical temperature (T c ). Reacted Ag forms a small amount (~1%) of Ag 2 Se impurity phase, which may increase the pinning energy in comparison with that of the undoped sample. The enhanced upper critical field (B c2 ) is also a result of the increased impurity scattering. Thus, unlike cuprates Ag addition enhances the T c , B c2 , pinning energy and MR making the properties of polycrystalline FeSe 0.94 similar to those of single crystals.

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Section: Resultssupporting

confidence: 93%

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

Nazarova

Balchev

Nenkov

et al. 2015

Supercond. Sci. Technol.

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“…Based on the Fe-Se binary phase diagram study [15][16][17] , with the changes of Fe:Se atomic ratio and sintering temperature, there are many FeSe binary phases including FeSe 2 , Fe 3 Se 4 and Fe 7 Se 8 , which can be formed with different lattice structures. Besides, a diffusion-less transformation process has been found that four different crystal orientations of the tetragonal β-FeSe phase can be formed from one hexagonal δ-FeSe grain [18] . Therefore, it can be deduced that the superconductivity of final product is very sensitive to the stoichiometry [19,20] .…”

Section: Introductionmentioning

confidence: 99%

The phase evolution mechanism in Fe(Se, Te) system

Liu¹,

Li²,

Zhang³

et al. 2016

Physica C: Superconductivity and its Applications

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“…18 Slight changing in sintering parameters and chemical composition can induce the appearing of non-superconducting hexagonal d-FeSe (and/or Fe 7 Se 8 ) phases, which decrease the superconducting volume weakening the intergrain connections, reducing the T c value of FeSe samples by varying the chemical composition of bFeSe phase. 17 In fact, it is very hard to avoid the appearance of secondary phase during the preparation of FeSe bulks and wires, [19][20][21][22] even single crystals, 23 but these impurities do not avoid the superconducting applications.…”

Section: Introductionmentioning

confidence: 99%

Nanosized tetragonal β-FeSe phase obtained by mechanical alloying: structural, microstructural, magnetic and electrical characterization

Ulbrich

Campos

2018

RSC Adv.

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Nanocrystalline tetragonal b-FeSe phase was prepared mechanochemically using ball milling procedures in an inert atmosphere, starting from Fe x Se powder mixtures with x ¼ 1.00, 1.25 and 1.50, with x ¼ 1.25 and 1.50 leading to more than 93% of pure phase after annealing at 400 C for 1 hour under vacuum. X-ray powder diffraction provides information on phase formation and phase transitions with milling time and temperature. The Rietveld method was used to refine the crystal structure, including the z coordinate of Se and occupancies, to determine the microstructure and to assess the amount of contaminant phases observed. Lattice contraction is found in the ab-plane more than along the c-axis, the small average size of crystalline domains (<22 nm) and the high microstrain (>1%) indicate the formation of highly strained nanoparticles. Magnetic and electrical characterization showed a poor superconductivity at 4 K and semiconducting properties only for thermally treated samples. These observations are explained by the presence of ferromagnetic impurity phases (residual Fe, hexagonal d-FeSe phase and monoclinic Fe 3 Se 4 ), but other effects caused by the mechanochemical synthesis must be considered, such as small average size, large/non-uniform size distribution and high microstrain of the nanosized tetragonal b-FeSe phase.The increase of the b-FeSe phase content with increasing storage time (ageing) above a few days to months in air, at RT and in the dark was observed for all as-milled samples. Preliminary data on the ageing effect are shown while a systematic study on this is in progress and will be presented elsewhere.

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Microstructure and phase transformations in FeSe superconductor

Cited by 22 publications

References 10 publications

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

Improvement of the superconducting properties of polycrystalline FeSe by silver addition

The phase evolution mechanism in Fe(Se, Te) system

Nanosized tetragonal β-FeSe phase obtained by mechanical alloying: structural, microstructural, magnetic and electrical characterization

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