Archimedean solidlike superconducting framework in phase-separatedK0.8Fe1.6+xSe2

Abstract

The superconducting (SC) phase in the phase-separated (PS) K 0.8 Fe 1.6+x Se 2 (0 ≤ x ≤ 0.15) materials is found to crystallize on Archimedean solid-like frameworks, this structural feature originate from a spinodal phase separation (SPS) at around T s ≈540K depending slightly on the Fe concentration.Two stable phases in K 0.8 Fe 1.6+x Se 2 are demonstrated to be the SC K 0.5 Fe 2 Se 2 and antiferromagnetic (AFM) K 0.8 Fe 1.6 Se 2 . The spinodal waves go along the systematic [113] direction and result in notable lamellar structure as illustrated by using the strain-field theoretical simulation. The 3-dimentional SC framework is constructed by hollow truncated octahedra similar with what discussed for Archimedean solids. Based on this structural model, we can efficiently calculate the volume fraction of SC phase in this type of PS SC materials.

Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystalKxFe2−ySeLiu1, Xing2, Straszheim3 et al. 2016Phys. Rev. B177280View full textAdd to dashboardCite

“…2(c) clearly shows only atomic ordering through atomic diffusion is needed for the phase separation. Our observations exclude the spinodal decomposition mechanism for the phase separation in K x Fe 2-y Se 2 pseudo single crystal as previously suggested [12]. [29], muon spin rotation (μSR) [30], and Mössbauer [31][32] spectroscopy have revealed nearly 90% of the sample volumes exhibit large-moment antiferromagnetic (AFM) order, while 10% of the sample volumes remain paramagnetic (PM) and attributed to a metallic/superconducting phase in A x Fe 2-y Se 2 single crystals.…”

“…In addition, the parallelepipeds lie in a {113} plane, change their directions within the {113} plane, branch, and bend into another {113} plane. The overall 3D arrangement of the parallelepipeds appears to form incomplete hollow hexahedra, rather than hollow truncated 15 octahedral Archimedean solids as speculated from 2D images [12]. parallelepipeds {113} planes and along <301> directions.…”

“…The temperature dependence of surface morphology clearly reveals that bright phase increases its fraction at the expense of the matrix. Above 305 °C, the contrast between the two phases completely disappears, which implies that the two phases form a 7 homogeneous solid solution, a single phase above T s [5,12]. Upon cooling, the SEM images show the visible contrast at 290 °C.…”

“…ubiquitous precipitation and growth with decreasing temperature across the tie line in the phase space [5]. The phase separation in K x Fe 2-y Se 2 had been ascribed to a spinodal decomposition later [12]. According to the theory of the spinodal decomposition [13][14], the high-temperature iron-vacancy-disordered phase will spontaneously decompose into the superconducting phase and the iron-vacancy-ordered phase below the phase separation temperature.…”

“…During the phase separation, the superconducting phase forms as the remnant of high-temperature phase while most of high-temperature phase, nearly 90%, is transformed into the iron-vacancy-ordered phase. In an early report by Wang et al, a model of hollow truncated octahedron in terms of Archimedean solids for the three dimensional (3D) microstructure in K x Fe 2-y Se 2 was conjectured, based on the SEM images obtained in (001), (110) and (100) surfaces [12].…”