Probing the Influence of Defects, Hydration, and Composition on Prussian Blue Analogues with Pressure

Abstract

The vast compositional space of Prussian blue analogues (PBAs), formula A x M[M′(CN) 6 ] y · n H 2 O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties—e.g., flexibility and propensity for phase transitions—is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus ( B 0 ≈ 6 GPa) for defective PBAs. Interstitial water increases B 0 and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN) 6 , but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN) 6 (A I = Rb, Cs) transition from F 4̅3 m to P 4̅ n 2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb 0.87 Mn[Co(CN) 6 ] 0.91 is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.

High-pressure behavior of heteroepitaxial core–shell particles made of Prussian blue analogs

“…The substitution of Cs by Rb presumably accounts for the large difference in K0 values for the two Co-Fe PBAs as these studies used close PXRD set-ups and a same Murnaghan EoS for fitting. This conclusion is in good agreement with a recent investigation comparing rubidium and cesium Mn-Co PBA, 25 but the impact of specific arrangements of the metallocyanide vacancies 51 as well as variations in the hydration level 25 between the two Co-Fe PBA samples cannot be discarded.…”

“…The large photostriction reported in Prussian blue analogues has been used to design artificial structures coupling photostrictive and magnetostrictive properties and could be further exploited to develop alternative opto-mechanical devices and sensors. For these compounds, most of the phenomena including photophysical properties relies on the elastic properties of the PBA network, but reports on their piezomagnetic properties or of their elastic constants are still limited despite recent efforts 24,25 to rationalize the apparent variability in the literature results.…”

“…Chemically-inert silicone oil (Prolabo, Rhodorsil 47V1000) was used as pressure-transmitting medium to prevent a dehydration of the samples as the hydration level of PBAs was recently shown to have an influence on their elastic properties. 24,25 Data were collected in transmission geometry at room temperature and constant wavelength (λ= 0.4523 Å, beam size: HV = 10040 µm 2 full width at half maximum). We used a 345 mm-diameter Mar Research image plate with 2 to 5 min exposure time and ± 5° rocking of the DAC.…”

“…𝜖 is typically of the order of 10 -3 for high-pressure synchrotron diffraction measurements. Considering the range of K0-values given in the literature for PBAs and other cyanometallate network solids, 24,25,30,45,49 pressure gradients should not exceed 0.02 GPa while this criteria relaxes to 0.17 GPa for gold. However, comparison between the single-phase Ni-Cr PBA particles and the same compound grown as a shell layer indicates that small rhombic distortion of the cubic cell has little influence on bulk modulus values, so that discrepancies observed in the literature rather reflect sample variability or fitting procedures.…”

Stepwise Stress‐Induced Transformations of Metal‐Organic Polyhedral Cluster‐Based Assemblies: Where Conformational and Supramolecular Features Meet

“…So far, comprehensive studies on crystals under high pressure have concerned mainly organic compounds and simple metal complexes with low nuclearity [12–14] or even hybrid organic‐inorganic metal halide perovskites [15,16] and porous metal‐organic frameworks (MOFs) [17,18] . For example, under pressure supramolecular coordination networks can undergo various structural transformations including lattice deformations and conformational movements of organic linkers, which often manifest in changes in physicochemical properties of materials [19–21] . Moreover, high pressure can trigger bond rearrangements and reversible phase transformations in MOFs [22] or control depolymerization of coordination polymers [23] .…”