Superconductivity Above 40 K Observed in a New Iron Arsenide Oxide (Fe₂As₂)(Ca₄(Mg,Ti)₃O_y)

Abstract

A new layered iron arsenide oxide (Fe 2 As 2 )(Ca 4 (Mg,Ti) 3 O y ) was discovered. Its crystal structure is tetragonal with a space group of I4=mmm consisted of the anti-fluorite type FeAs layer and blocking layer of triple perovskite cells and is identical with (Fe 2 As 2 )(Sr 4 (Sc,Ti) 3 O 8 ) discovered in our previous study. The lattice constants of (Fe 2 As 2 )(Ca 4 (Mg,Ti) 3 O y ) are a ¼ 3:877A and c ¼ 33:37 A. This compound exhibited bulk superconductivity up to 43 K in susceptibility measurement without intentional carrier doping. A resistivity drop was observed at 47 K and zero resistance was achieved at 42 K. These values correspond to the second highest T c among the layered iron-based superconductors after REFeAsO system. #

Superconductivity at 28.3 and 17.1 K in (Ca4Al2O6−y)(Fe2Pn2) (Pn=As and P)

“…Most recent achievement is the discovery of superconductors possessing perovskitetype blocking layers, (Sr 4 Sc 2 O 6 )(Fe 2 P 2 ) [4], (Sr 4 M 2 O 6-y )(Fe 2 As 2 ) (M = V [5] and MgTi [6]), (Sr 4 M 3 O 8 )(Fe 2 As 2 ) (M = ScTi ), (Ba 4 Sc 3 O 7.5 )(Fe 2 As 2 ) [7], (Ca n+m (M,Ti) n O y )(Fe 2 As 2 ) (M = Sc [8], Mg [9,10] and Al [11], n = 2, 3, 4 and 5, m = 1, 2 ), with T c reaching as high as 47 K for (Ca 4 (Mg,Ti) 3 O y )(Fe 2 As 2 ). Another interesting feature is the strong correlation between their superconducting transition temperature (T c ) and the configuration of the FeAs 4 local structure, such as the Pn-Fe-Pn bond angle (α) and/or the height of Pn atoms relative to the neighboring Fe layers (h Pn ) [12, superconductors (Ln=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy) that possess small Ln atoms, which yield small LnO blocking layers [17].…”

NMR investigation of the iron-based superconductors Ca4(Mg,Ti)3Fe2AsTomita1, Kotegawa2, Tao3 et al. 2012Phys. Rev. B

“…[1,8] The MgTi:3 exhibits T onset c = 47 K in a resistivity measurement, which is the highest value among perovskite systems. [1] The presence of a clear diamagnetism is confirmed below 43 K. The T onset c of ScTi:4 is 41 K as per a resistivity measurement, and diamagnetism is observed below 36 K. [8] The nominal composition of each compounds is given as Ca 4 (Mg 0.25 Ti 0.75 ) 3 Fe 2 As 2 O 8−y and Ca 5 (Sc 0.5 Ti 0.5 ) 4 Fe 2 As 2 O 11−y , however the doping level is unclear due to a difficulty of the quantitative analysis of the stoichiometric ratio. The samples were crushed into powder for NMR measurements.…”

“…The maximum T c in the perovskite-type systems has been marked at T onset c ∼ 47 K for Ca 4 (Mg,Ti) 3 Fe 2 As 2 O 8−y or T onset c ∼ 46 K for pressurized Sr 2 VFeAsO 3 . [1,2] The perovskite systems have a tendency that the pnictogen height is longer and the AsFe-As bond angle is sharper compared with 1111 systems possessing the same a-axis length, [3] and the systems have many varieties of the blocking layers. T c of over 40 K has been achieved only in 1111 systems and perovskitetype systems, thereby implying the importance of the structural feature for achieving higher values of T c .…”

“…[1,[4][5][6][7][8][9][10] Figure 1 shows the crystal structures of the latter type, Ca n+1 M n Fe 2 As 2 O 3n−1 (n = 3 and 4). The thick blocking layer composed of Ca n+1 M n O 3n−1 expands the distance between FeAs layers along the c axis, and this layer distance ranges from ∼ 15to25 A.…”

Electronic band structure and Fermi surface of new low-temperature Ni-based superconductors: 3.3K (Ni2P2)(Sr4Sc2O6) and 2.7K (Ni2As2)(Sr4Sc2O6) from first principles

“…Another remarkable feature of these perovskite-like oxide blocks is high structural flexibility: their thickness can be controlled according to the composition and synthesis conditions. In this way very recently a new series of homologous superconductors with T c to 42K having thicker oxide layers such as (Fe 2 As 2 )(Ca n+1 (Sc,Ti) n O y ), where n = 3, 4, and 5, and y ~ 3n-1, and isostructural (Fe 2 As 2 )(Ca n+1 (Mg,Ti) n O y ) with n=5 was discovered [23][24][25][26].…”