Atomically imaged crystal structure and normal-state properties of superconducting Ca10Pt4As8((Fe1–xPtx)2As2)5

Superconducting Ca₁₀Pt₄As₈(Fe₂As₂)₅ is rare because optimal superconducting transition temperature is achieved without chemical doping or pressure. Furthermore, the unclear crystal structure limits our ability to understand the structure-property relationship. Using atomically resolved scanning transmission electron microscopy and electron diffraction, we directly determine the structure of this superconductor: it forms a monoclinic structure (space group P2₁/n) with lattice parameters a = b = 8.76Å, c = 20.18Å, and γ = 90.5°. Compared with previously reported structures derived from diffraction experiments, the c-lattice constant is doubled due to alternating stacking of Pt₄As₈ layers, which induces a high density of stacking faults. With the establishment of the crystal structure, stacking faults, and chemical composition, the distinctive normal-state electrical and thermal transport properties of our superconducting Ca₁₀Pt₄As₈((Fe_1–xPt_x)₂As₂)₅ (x ~ 0.05) single crystals can be explained.