Pressure-induced amorphization and decomposition ofFe[Co(CN)6]

Abstract

The high-pressure behavior of the Prussian Blue analogue Fe͓Co͑CN͒ 6 ͔ has been explored by energy-and angle-dispersive x-ray diffraction, Fourier transform infrared, and Raman spectroscopy. This cyanide-bridged framework material becomes x-ray amorphous above 10 GPa and the high-pressure form is retained upon pressure release. Samples recovered from around 17 GPa exhibit a dark, metallic luster and their Raman spectra are characteristic of amorphous CN x films. These observations constitute strong evidence that Fe͓Co͑CN͒ 6 ͔ decomposes at high pressures.

Pressure-enhanced decomposition of Ag3[Co(CN)6]

“…It strongly resembles a band assigned to graphitelike amorphous carbon nitride (CN x ) [31][32][33][34]. Interestingly, similar results were obtained for the recovered amorphous phase produced by compression of Fe[Co(CN) 6 ] to 17.4 GPa and Ag 3 [Co(CN) 6 ] to 14 GPa at room temperature [3,22,35]. Fig.…”

“…Raman spectroscopy at room conditions of the samples decomposed at high pressure confirms the presence of a X-ray amorphous phase, which keeps a close similarity with the amorphous phase obtained by the pressure induced structural destabilization of Fe[Co(CN) 6 ], other framework structured metal-cyanide [3,22,35] The results indicate that in the case of Ag 3 [Co(CN) 6 ], as already observed for Fe[Co(CN) 6 ], the mechanisms that determine NTE and PIA are not the same. The two phenomena are observed in these metal cyanides due to the high flexibility of their associated structures.…”

“…Both the structural disordering and the observed phase transitions were shown to be strongly sensitive to the degree of deviatoric stress to which the sample was subjected. At room temperature, Fe[Co(CN) 6 ] becomes X-ray amorphous above 10 GPa and the high pressure form is retained upon pressure release [22]. The amorphization of Fe[Co(CN) 6 ] was interpreted as the result of a hindered decomposition, in which one of the products is an amorphous CN x phase, as identified by Raman spectroscopy.…”

Lattice dynamics and thermal expansion behavior in the metal cyanidesMCN(M=Cu, Ag, Au): Neutron inelastic scattering and first-principles calculations

“…The cyanide compounds are found to exhibit the phenomenon of negative linear compressibility. The c-axis in Ag 3 Co(CN) 6 is found to show NTE as well as negative linear compressibility 9,18,[34][35][36][37] behavior. KMn[Ag(CN) 2 ] 3 shows extreme negative compressibility mediated by selective soft-mode frustration 38 .…”

First phase commissioning of high pressure XAFS setup at ED-XAFS beamline, Indus-2 synchrotron radiation source, India

“…Understanding structural changes of materials under high pressure have direct bearing on contemporary practical applications since nano-sized systems are inherently subject to high surface pressure. Problems of our current interest include high pressure transitions (0-40GPa) in Negative Thermal Expansion (NTE) materials [23][24][25],Fe-based superconductors [26,27], perovskites (BiFeO 3 [28], BaLiF 3 [29], Sr 2 MgWO 6 [30]), pyrochlores (Yb 2 Ti 2 O 7 [31], LaHf 2 O 7 [32], Rare earth oxides (Dy 2 O 3 [33], CeO 2 [34], CeVO 4 [35], Nd 2 O 3 [36]), metal-filled carbon nanotubes [37], Zn(CN) 2 [38].…”