Structural Phase Separation in K_0.8Fe_1.6+xSe₂ Superconductors

Abstract

Structural investigations on the K0.8Fe1.6+x Se2 superconducting materials have revealed microstripes arising from phase separation. Two coexisting structural phases can be characterized by modulations of q 1 = 1/5[3a* + b*], the antiferromagnetic phase K0.8Fe1.6Se2, and q 2 = 1/2[a* + b*], the superconducting phase K y Fe2Se2, respectively. These stripe patterns also show visible correlation with the anisotropic assembly of superconducting particles along the [110] and [11̅0] directions. In addition to the notable stripe structures, a nanoscale phase separation also appears in the present superconducting system as clearly observed by high-resolution transmission electron microscopy. Certain nanoscale structural features in this heterogeneous system can be qualitatively understood by the percolation scenario.

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

“…We 9 also notice that transmission electron microscopy (TEM) measurements found at least three different Fe-vacancy orders in the FeSe system [25]. It was already reported the superconducting phase may have a potassium-vacancy-ordered superstructure [17,26]. Interestingly, the superconducting phase seems to be mediated by an interface phase, which protects metallic percolative paths in K x Fe 2-y Se 2 superconductors [27].…”

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…Although there is ample evidence indicating that the superconducting alkali iron selenides are mesoscopically phase separated from the insulating A 2 Fe 4 Se 5 phase with the √ 5 × √ 5 block AF structure as shown in Fig. 2(d) (Carr et al, 2014;Charnukha et al, 2012;Ksenofontov et al, 2011;Li et al, 2011b;Ricci et al, 2011;Shermadini et al, 2012;Shoemaker et al, 2012;Speller et al, 2012;Texier et al, 2012;Wang et al, 2012c), there is still no consensus on the chemical and magnetic structures of their parent compounds (May et al, 2012;Wang et al, 2011b;Ye et al, 2011;Zhao et al, 2012). Assuming that the insulating A 2 Fe 4 Se 5 phase is the parent compound of the superconducting A x Fe 2−y Se 2 , its spin waves have been mapped out by several groups (Chi et al, 2013;Wang et al, 2011c;Xiao et al, 2013).…”

Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides

“…The commonly observed 245 phase exists in all the nominal compositions of Rb 0.8 Fe 2 Se 2−z S z as a mesoscopically separated phase. Note that the Fe content is in fact less than 2 which means that all of the samples are in the two phase coexistence region [11][12][13][14][15][16][17][18][19][20][21][22][23] .…”

“…1 (x ≈ 0.8, y ≈ 1.6, referred to as the 245 phase) always seems to be mesoscopically interdigitated with the SC phase that has been suggested to be an iron vacancy free phase in the studies to-date [10][11][12][13][14][15][16][17][18][19][20][21][22][23] . The relationships between the two phases are still under debate.…”