Abstract
Contrast to superconducting compounds SrNi <sub>2</sub> Ge <sub>2</sub> (T <sub>c</sub> = 1.1 K) and SrPd <sub>2</sub> Ge <sub>2</sub> (T <sub>c</sub> = 3.2 K) with the BaFe <sub>2</sub> -As <sub>2</sub> -type body-center-tetragonal (122-bct) layer structure (space group I4/mmm), SrPt <sub>2</sub> Ge <sub>2</sub> crystallized in a pseudo-tetragonal, monoclinic structure with space group P21 and lattice parameters a = 0.4401(4) nm< b = 0.4435(4) nm, c = 0.9764(10) nm and β = 90.5° >90°. Superconductivity with T <sub>c</sub> =10.2K was observed in this new compound. However, a weak diamagnetic shielding signal of -3.2 × 10 <sup>2</sup> cm <sup>3</sup> /mol at 2K indicates that superconductivity is not from the bulk monoclinic phase but from a minor metastable 122-bct high-temperature phase with a ∼ 0.44 nm, c ∼ 0.98 nm, β = 90°. This is the highest T <sub>c</sub> reported outside the iron-based layer compounds with the 122-bct structure. High-T <sub>c</sub> superconductivity is due to strong quasi-2D Pt-Ge-Pt 5d <sub>xz, yz</sub> -4p-5d <sub>xz, yz</sub> hybridization in the Pt-Ge layer with squeezed PtGe4 tetrahedral crystal field and Pt-5d <sup>8</sup> spin-orbital interaction in the metastable 122-bct phase and is another example of multi-band (d <sub>xz</sub> /dy <sub>z</sub> /d <sub>xy</sub> ) non-conventional s-wave superconductor. © 2013 Elsevier B.V. All rights reserved.