Negative thermal expansion in cubic FeFe(CN)₆ Prussian blue analogues

Abstract

A new isotropic negative thermal expansion compound of FeFe(CN)6 has been found, in which the transverse vibrations of N atoms dominate in its NTE behavior.

Strong Negative Thermal Expansion in a Low-Cost and Facile Oxide of Cu2P2O7

“…Consequently, the NTE in Cu 2 P 2 O 7 could result from the coupling twist and rotation of neighbor rigid polyhedra. The NTE nature of Cu 2 P 2 O 7 is entangled with RUMs, which is similar to some framework structure NTE materials, such as ZrW 2 O 8 , ScF 3 , and Prussian blue analogues …”

“…and NaZn 13 -type compounds, − ferroelectric phase transitions in perovskite (ABO 3 ) group, , size effect in nanoparticles, and valence transition in some oxides. − Note that those electron-driven NTE behaviors can present a strong NTE magnitude but a relatively narrow temperature range . As a comparison, the low-frequency phonon driven NTE materials have a merit of wider NTE temperature range but relatively small NTE magnitude, such as oxides, − fluorides, , cyanides, , Prussian blue analogues (PBAs), − and metal–organic frameworks (MOFs). , All the low-energy phonon driven NTE materials own a common character of framework structure which is in corner shared tetrahedral or octahedral units through M–O–M, M–F–M, or M–CN–M bridges. Generally, flexible framework structures with soft chemical bonds can contribute to a stronger NTE behavior, thus the NTE in oxides or fluorides is generally smaller than that in PBAs or MOFs.…”

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

“…74 Fully oxidized, cubic FeFe(CN) 6 is structurally invariant to hydration. 85 In effect, water acts as a transition modifierit cannot induce phase transitions in cubic PBAs, but it dictates which transition occurs upon hydrostatic compression or Na I inclusion. It is noteworthy that dehydrated Na 2 FeFe(CN) 6 shows the same rhombohedral structure as hydrated MnPt•nH 2 O under compression.…”

“…Dehydrated Na 2 FeFe­(CN) 6 crystallizes in R 3̅ (tilt system a – a – a – , ), whereas the hydrated version adopts P 2 1 / n symmetry ( a – a – c + ) . Fully oxidized, cubic FeFe­(CN) 6 is structurally invariant to hydration . In effect, water acts as a transition modifierit cannot induce phase transitions in cubic PBAs, but it dictates which transition occurs upon hydrostatic compression or Na I inclusion.…”

EXAFS spectroscopy: a powerful tool for the study of local vibrational dynamics

“…It was found that NTE is induced by the transverse vibrations of the atomic -M-N≡C-M'-linkages through a tension mechanism, since both M-N and M'-C bonds are much softer to bend than to stretch. However, the main vibrational contribution to the NTE comes from the N atoms, since the relative transverse vibrations of the M-N bonds are much larger than that of the M'-C bonds [Figure 17] [113][114][115] . shows the resulting anisotropy of the relative thermal vibrations.…”