Phase diagram and superconductivity at 58.1 K in α-FeAs-free SmFeAsO_1−xF_x

Abstract

The Phase diagram of SmFeAsO 1-x F x in terms of x is exhibited in this study. SmFeAsO 1-x F x from x = 0 to x = 0.3 were prepared by low temperature sintering with slow cooling. The low temperature sintering suppresses the formation of the amorphous FeAs, which is inevitably produced as an impurity by using high temperature sintering. Moreover, slow cooling is effective to obtain the high fluorine concentration.The compositional change from feedstock composition is quite small after this synthesis. We can reproducibly observe a record superconducting transition for an iron based superconductor at 58.1 K.This achievement of a high superconducting transition is due to the success in a large amount of fluorine substitution. A shrinking of the a lattice parameter caused by fluorine substitution is observed and the substitutional rate of fluorine changes at x =0.16.

Controlling factors of <i>T<span class="aps-inline-formula"><math><msub><mrow></mrow><mi>c</mi></msub></math></span></i> dome structure in 1111-type iron arsenide superconductors

“…[9][10][11] Superconductivity, with a critical temperature Tc of up to 57.8 K, 12,13 emerges when the structural-magnetic transition is suppressed by electron doping of the FeAs-layer via fluoride ion (F − ) substitution of oxygen sites. The doped electron concentration x vs temperature T diagram of LnFeAsO1−xFx possess a superconducting (SC) region in the range x = 0.1-0.2 adjacent to an antiferromagnetic (AFM) region at x ≈ 0.0, 14 although the whole shape of the SC region has not been determined because the solubility limit of F − restricts x to <0.2.…”

Amorphous FeAs-free SmFeAsO1−xFxusing low temperature sintering with slow cooling

“…However, the resistivity of the normal state continues to decrease and T c onset also continues to increase with increasing x as shown in figure 3. As a result, maximum T c is observed at 58.1 K [8]. This suggests that fluorine continues to be gradually introduced into SmFeAsO 1-x F x above x = 0.16.…”

The effect of exceptionally high fluorine doping on the anisotropy of single crystalline SmFeAsO1−xFx

“…However, the low temperature sintering makes it possible. The current highest T c (58.1 K) in iron pnictides is obtained by this method 10 . T c drastically increases up to around 55 K, and the a lattice parameter rapidly decreases until x = 0.15.…”