Superconductivity at 3 85 K in BaPd 2 As 2 with the
The single crystal of ThCr2Si2 type BaPd2As2 was successfully prepared by a self flux method, and the crystal structure was characterized by X ray diffraction method with the lattice parameters a 4.489(2) A and c 10.322(3) A (space group I4/mmm, No. 139) Bulk superconductivity below a Tc (critical temperature) of 3.85 K was revealed in this compound by the measurements of resistivity, magnetic susceptibility and specific heat, and this Tc is much higher than those of other isostructural Pd based superconductors. editor's choice Copyright c (c) EPLA, 2016 Introduction. Transition metal compounds have been widely studied due to their intriguing physical properties which usually originate from the strongly correlated d electrons, especially for the search of high Tc (Tc is critical temperature) superconductors [1 3] Among the new high Tc family of iron pnictide superconductors, the ternary parent compounds AFe2As2 (A Ca, Sr, Ba, etc. belong to a common ThCr2Si2 type crystal structure, and they are spin density wave (SDW) semimetals at low temperature. Superconductivity can be induced after suppressing the SDW order by chemical doping, external pressure or internal crystal defects, for instance the Ba1 xKxFe2As2 superconducts at 38 K [4 6] Many recent works were focused on these 122 type ternary superconductors to solve the hidden pairing mechanism in these high Tc materials, mostly because that high quality single crystal samples can be easily synthesized for these inter metallic compounds [7 10] Moreover, most of the transition metals can form this simple body centered tetragonal ThCr2Si2 type crystal structure, and to study similar materials within this structure may be an easy route for the search of new superconductors. Some of these iron free compounds were already reported to be superconductors, such as SrNi2As2, (a)E mail: renzhian@iphy.ac.cn LaRu2P2, BaRh2P2, SrPd2Ge2, SrIr2As2, etc. while their superconducting Tc is all very low within several degrees Kelvin [11 14] Recently, Anand et al. prepared single crystals of APd2As2 (A Ca, Sr, Ba) by PdAs flux [15] and reported superconductivity for CaPd2As2 and SrPd2As2 which both crystallize in the collapsed ThCr2Si2 type structure; while BaPd2As2 crystallizes in the tetragonal CeMg2Si2 type structure without bulk superconductivity. The transition metal Pd containing ThCr2Si2 type compounds have been studied by several groups, and some discovered superconductors are LaPd2Ge2 (Tc 1.12 K) [16] CaPd2Ge2 (Tc 1.98 K) [17] SrPd2Ge2 (Tc 3.04 K) [14] CaPd2As2 (Tc 1.27 K) SrPd2As2 (Tc 0.92 K) [15] and LaPd2As2 (Tc 1 K) etc. [18] Another 122 type LaPd2Sb2 (Tc 1.4 K) superconductor forms in a CaBe2Ge2 type structure [19] We have carefully studied the Ba Pd As ternary phases, and prepared three polymorphs of the BaPd2As2 compounds, namely the CeMg2Si2 type [20] the BaPd2As2 type [20] and the ThCr2Si2 type [21] and found that superconductivity only exists in the last structure with measurements above 1.8 K. Here we report the preparation of the ThCr2Si2 type BaPd2As2 single crystal, and bulk superconductivity was revealed in it by resistivity, magnetization and specific heat measurements with a Tc of 3.85 K,