Premium
Density‐functional‐theory‐predicted symmetry lowering from cubic to tetragonal in nickel hexacyanoferrate
Author(s) -
Ghazisaeed Seyedayat,
Minuddin Md,
Nakotte Heinz,
Kiefer Boris
Publication year - 2020
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576719016492
Subject(s) - tetragonal crystal system , density functional theory , nickel , van der waals force , crystal structure , crystallography , chemistry , molecule , formula unit , prussian blue , computational chemistry , materials science , organic chemistry , electrode , electrochemistry
Density‐functional‐theory (DFT) computations on a Prussian blue analogue (PBA), nickel hexacyanoferrate, Ni 2+ 3 [Fe 3+ (CN) 6 ] 2 · n H 2 O, predict the existence of a tetragonal ( P 4 m 2) crystal structure that is energetically degenerate with the previously reported cubic ( F 4 3 m ) structure for this PBA. The proposed tetragonal structure satisfies observations, such as X‐ray diffraction and magnetic measurements, that have been reported previously. A van der Waals corrected exchange‐correlation functional is used in the DFT+U computations for an improved description of hydrogen bonding. The results provide strong support for a revised and simplified crystallographic description of Ni 2+ 3 [Fe 3+ (CN) 6 ] 2 · n H 2 O, and show how H 2 O molecules stabilize the crystal structure and affect its magnetic and electronic properties. The symmetry lowering in nickel hexacyanoferrate is attributed to the hydration shell of the interstitial nickel cation. Calculations strongly suggest a maximum of n = 7 interstitial H 2 O molecules per formula unit for nickel hexacyanoferrate at room temperature, and a higher water content at temperatures below T ≃ 200 K. Since the symmetry lowering relies on the presence of interstitial H 2 O molecules, this revised crystallographic description may be applicable more generally to the large class of F 4 3 m ‐structured PBAs.