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DOE OSTI2020

Materials Data on Cs2NaYI6 by Materials Project

Cs2NaYI6 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Cs1+ is bonded to twelve equivalent I1- atoms to form CsI12 cuboctahedra that share corners with twelve equivalent CsI12 cuboctahedra, faces with six equivalent CsI12 cuboctahedra, faces with four equivalent NaI6 octahedra, and faces with four equivalent YI6 octahedra. All Cs–I bond lengths are 4.38 Å. Na1+ is bonded to six equivalent I1- atoms to form NaI6 octahedra that share corners with six equivalent YI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Na–I bond lengths are 3.17 Å. Y3+ is bonded to six equivalent I1- atoms to form YI6 octahedra that share corners with six equivalent NaI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Y–I bond lengths are 3.03 Å. I1- is bonded in a distorted linear geometry to four equivalent Cs1+, one Na1+, and one Y3+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Iodide Double Perovskites and the Limits of their Structural Stability

AbstractWhile halide double perovskites A2M(I)M(III)X6 have attracted significant attention, examples involving iodides are rare. We examine the limits of the structural stability of iodide double perovskites, presenting the synthesis and single‐crystal structures of Cs2NaScI6 and Cs2NaYI6. Bypassing the common expectation that iodides have small band gaps, these compounds display optical gaps of 3.10 eV [M(III) = Sc] and 3.65 eV [M(III) = Y]. Cs2NaScI6 is the only iodide double perovskite to exhibit a cubic crystal structure at room temperature. Density functional theory‐based electronic structure calculations help understand the role of competing Cs3M(III)2I9 (3 : 2 : 9) phases and provide possible reasons for why iodide double perovskites based around In(III), Sb(III) and Bi(III) cations have proved elusive. We confirm design rules for halide double perovskites based around concepts of the tolerance factor and the radius ratio of the smaller, trivalent ion, but also point to situations such as what is observed for Cs2NaScI6 where a double perovskite can be trapped in a metastable structure.

Mulligan, Anya S.↗