Results for “Cs2NaBiCl6” | Engineering Papers

DOE OSTI2020

Materials Data on Cs2NaBiCl6 by Materials Project

Cs2NaBiCl6 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 Cl1- atoms to form CsCl12 cuboctahedra that share corners with twelve equivalent CsCl12 cuboctahedra, faces with six equivalent CsCl12 cuboctahedra, faces with four equivalent NaCl6 octahedra, and faces with four equivalent BiCl6 octahedra. All Cs–Cl bond lengths are 3.91 Å. Na1+ is bonded to six equivalent Cl1- atoms to form NaCl6 octahedra that share corners with six equivalent BiCl6 octahedra and faces with eight equivalent CsCl12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Na–Cl bond lengths are 2.80 Å. Bi3+ is bonded to six equivalent Cl1- atoms to form BiCl6 octahedra that share corners with six equivalent NaCl6 octahedra and faces with eight equivalent CsCl12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Bi–Cl bond lengths are 2.73 Å. Cl1- is bonded in a distorted linear geometry to four equivalent Cs1+, one Na1+, and one Bi3+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Structural Propensities in Cs2MBiX6 (M=Na, Ag; X=Cl, Br) Bismuth Halide Double Perovskites

A previously unreported low-temperature phase transition in the bismuth halide double perovskite Cs2AgBiCl6 is reported, thereby establishing trends in the structural ground state across Cs2NaBiCl6, Cs2AgBiCl6, and Cs2AgBiBr6. Using the combined toolkit of variable-temperature synchrotron X-ray and neutron powder diffraction, Raman spectroscopy, and density-functional theory–based electronic structure modeling, we demonstrate a cubic Fm¯3m → tetragonal I4/m transition upon cooling with distinct onset temperatures. Neutron powder diffraction refinements permit the unambiguously assignment of the low-temperature phase of Cs2NaBiCl6 to I4/m, correcting prior reports of an I4/mmm ground state. Cs2AgBiCl6 is also found to transforms to a structure crystallizing in the I4/m space group at low temperatures. Temperaturedependent Raman data and density-functional theory-based modeling capture the softening and freezing of out-of-phase octahedral-tilt modes and quantify relative instabilities. Solid-state nuclear magnetic resonance spectroscopy at room temperature completes the characterization and helps underpin the subtle differences in covalency across the compounds. Trends in the phase transition temperature Ts and tilt magnitudes emerge from coupled effects of halide identity, M(I)–site bonding character, and a mismatch between interatomic distances. These results establish the structure– dynamics–bonding framework for tuning tilt-driven instabilities in halide double perovskites.

Tian, Haowen↗