Increase in T c and Change of Crystal Structure by High-Pressure Annealing in BiS2-Based Superconductor CeO0.3 F 0.7BiS2

Abstract

Recently, several types of BiS 2 -based superconductor such as Bi 4 O 4 S 3 , REO 1-x F x BiS 2 (RE: rare earth) and Sr 1-x La x FBiS 2 have been discovered. In this study, we have investigated the crystal structure and the superconducting properties for two kinds of polycrystalline samples (As-grown and high-pressure-annealed samples) of the BiS 2 -based superconductor CeO 0.3 F 0.7 BiS 2 . We found that both the As-grown and the high-pressure-annealed CeO 0.3 F 0.7 BiS 2 samples show bulk superconductivity. A higher T c was observed in the high-pressure-annealed sample.The T c of CeO 0.3 F 0.7 BiS 2 increased from T c zero = 2.7 K to T c zero = 3.7 K by high-pressure annealing. The lattice constant of a and c axis did not show remarkable differences between the As-grown and the high-pressure-annealed samples. Nevertheless, the peak symmetry of the (200) peak seemed to become more symmetric while the (004) peak did not show such a difference, indicating that the crystal structure within the ab plane changed to a higher-symmetric phase, a perfect tetragonal, by high-pressure annealing in CeO 0.3 F 0.7 BiS 2 .2

Superconductivity in layered BiS2-based compounds

“…2) has been reported for Bi 4 O 4 S 3 [55], which might suggest that the larger bending of the Bi-S-Bi bond is responsible for superconductivity. A similar distortion of the Bi-S layers 125 in LaO 1−x F x BiS 2 , CeO 1−x F x BiS 2 , and PrO 0.5 F 0.5 BiS 2 has also been observed [36,37,56,46]; the distortion of the Bi-S layers could be attributed to a fully occupied Bi s-orbital. Chemical substitution of F for O is considered to induce charge carriers into the Bi-S layer, and this is believed to induce supercon-130 ductivity in the mixed-anion layered compounds LnO 1−x F x BiS 2 (Ln = La, Ce, Pr, Nd, Yb) [6,36,8,37,15,38,39,40,41,42].…”

Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM

“…4(b) and (d) the diamagnetic response is clearly seen in the virgin low field region (from which H c1 is easily estimated to be ~44 Oe and 40 Oe for x  = 0.5 and 1.0 respectively. It is important to point out that in the selenium-free compound Sr 0.5 Ce 0.5 FBiS 2 ( T c  ~ 2.6 K & T FM  ~ 7.5 K)2744 and in a similar material Ce(O, F)BiS 2 ( T c  ~ 2.5–4 K & T FM  ~ 6.5–7.5 K)20525367 no superconducting hysteresis loop was observed. This is consistent with our own results on Sr 0.5 Ce 0.5 FBiS 2 (inset of Fig.…”

High-pressure effects on La(O,F)BiS2 single crystal using diamond anvil cell with dual-probe diamond electrodes

“…The compositional ratio was determined to be La:Bi:S = 1:0.99:1.72, by normalizing La = 1 in the EDX analysis, which is consistent with the cation composition of La(O,F)BiS2. The single crystal XRD analysis revealed that the compound crystallizes with a tetragonal structure, with typical lattice constants of a = 4.0541 (15) Å and c = 13.4826(52) Å. The EDX and XRD analyses establish that the obtained products are La(O,F)BiS2 single crystals.…”