Phonons and colossal thermal expansion behavior of Ag3Co(CN)6and Ag3Fe(CN)6

Mittal, R.; Zbiri, Mohamed; Schober, H.; Achary, S.N.; Tyagi, A. K.; Chaplot, S. L.

doi:10.1088/0953-8984/24/50/505404

Cited by 19 publications

(66 citation statements)

References 35 publications

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“…We find that there is a slight deviation between the experimental data [1] and the calculations at low temperatures due to the underestimation of the contribution from low energy phonon modes. Similar underestimation of the anharmonicity of low energy phonon modes is also found in cases of Zn(CN) 2 [24] as well as Ag 3 M(CN) 6 (M=Co,Fe) [25]. The contribution of phonon density of states at energy E to the thermal expansion has been determined (Fig.…”

supporting

confidence: 72%

Negative thermal expansion in cubic ZrW2O8: Role of phonons in the entire Brillouin zone fromab initiocalculations

Gupta

Chaplot

2013

Phys. Rev. B

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We report ab-inito density functional theory calculation of phonons in cubic phase of ZrW 2 O 8 in the entire Brillouin zone and identify specific anharmonic phonons that are responsible for large negative thermal expansion (NTE) in terms of translation, rotation and distortion of WO 4 and ZrO 6 . We have used density functional calculations to interpret the experimental phonon spectra as a function of pressure and temperature as reported in literature. We discover that the phonons showing anharmonicty with temperature are different from those showing anharmonicity with pressure although both are of similar frequencies. Only the latter phonons are associated with NTE. Therefore the cubic and/or quadratic anharmonicity of phonons is not relevant to NTE but just the volume dependence of frequencies. The calculations are able to reproduce the observed anomalous trends, namely, the softening of the low frequency peak at about 5 meV in the phonon spectra with pressure and its hardening with temperature, while both the changes involve a compression of the lattice. Earlier neutron scattering data [9] as well as theoretical [8] estimates of the anharmonicty of the phonons in ZrW 2 O 8 using interatomic potential model indicated that modes of energy below 8 meV are responsible for observed NTE. However estimates based on the Raman spectroscopy showed [7] that several modes nearly upto 50 meV contribute to NTE. The large disagreement in the energy range as well as nature of the low-energy modes in previous works indicated the need for understanding of NTE behaviour in ZrW 2 O 8 using ab-inito calculations. Recently ab-initio calculations of zone center phonon modes have been published [6]. However the authors concluded [6] that one should fully explore the nature of the phonons in the entire Brillouin zone for understanding the mechanism of NTE in cubic ZrW 2 O 8 . Here we report such a comprehensive calculations and identify specific zoneboundary modes that are highly anharmonic. The calculations are able to reproduce the observed NTE in cubic ZrW 2 O 8 as well as anomalous trends of the phonon spectra with increase in temperature and pressure.Important soft modes were identified in cubic ReO 3 [13] and ScF 3 [14] at M and R-points in the Brillouin zone respectively. These modes show simultaneously both large negative Grüneisen parameter as well as large quadratic anharmonicity, the former leading to NTE and latter to the temperature dependence. In case of ZrW 2 O 8 , we find that the modes that show large negative Grüneisen parameter contribute to NTE are not necessarily the same as those showing cubic and/or quadratic anharmonicity and significant temperature dependence. This finding means that the modes found anharmonic in temperature dependent measurements are not necessarily relevant to NTE.The first-principle calculations of lattice dynamics have been performed using Vienna Ab-initio Simulation Package (VASP) [15,16].The generalized gradient approximation (GGA) exchange correlation given by Perdew Becke and Ern...

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confidence: 72%

Negative thermal expansion in cubic ZrW2O8: Role of phonons in the entire Brillouin zone fromab initiocalculations

Gupta

Chaplot

2013

Phys. Rev. B

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“…With respect to Cu 3 [Co(CN) 6 ], further spectroscopic and lattice dynamical studies will likely prove valuable in understanding more deeply the microscopic origin of its NTE response, as has been the case for the other materials in this family [64,65]. While it has not been computationally feasible in our study to extend the MBD calculations to finite temperatures, a clear computational challenge for future investigations is the calculation of the phonon dispersion relation and thermal expansivity tensor of Cu 3 [Co(CN) 6 ], including MBD effects.…”

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confidence: 99%

Uniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]

Sapnik

Liu

Boström

et al. 2018

Journal of Solid State Chemistry

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We report the synthesis and structural characterisation of the molecular framework copper(I) hexacyanocobaltate(III), Cu 3 [Co(CN) 6 ], which we find to be isostructural to H 3 [Co(CN) 6 ] and the colossal negative thermal expansion material Ag 3 [Co(CN) 6 ]. Using synchrotron X-ray powder diffraction measurements, we find strong positive and negative thermal expansion behaviour respectively perpendicular and parallel to the trigonal crystal axis: α = 25.4(5) MK . These opposing effects collectively result in a volume expansivity α = 7.4(11) MK V −1 that is remarkably small for an anisotropic molecular framework. This thermal response is discussed in the context of the behaviour of the analogous H-and Ag-containing systems. We make use of density-functional theory with many-body dispersion interactions (DFT + MBD) to demonstrate that Cu + …Cu + metallophilic ('cuprophilic') interactions are significantly weaker in Cu 3 [Co(CN) 6 ] than Ag + …Ag + interactions in Ag 3 [Co(CN) 6 ], but that this lowering of energy scale counterintuitively translates to a more moderate-rather than enhanced-degree of structural flexibility. The same conclusion is drawn from consideration of a simple GULP model, which we also present here. Our results demonstrate that strong interactions can actually be exploited in the design of ultra-responsive materials if those interactions are set up to act in tension.

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“…As shown in Fig. 1, the ambient-pressure phase of Ag 3 Co(CN) 6 has a trigonal structure with space group P31m. The structure consists of layers of Kagome sheets of Ag atoms in the (001) crystal plane at height z = 1/2, with Co-CN-Ag-NC-Co chains along the 011 lattice directions linking [Co(CN) 6 ] 3− octahedra.…”

Section: Introductionmentioning

confidence: 99%

“…Ag 3 Co(CN) 6 has attracted a lot of attention due to its colossal positive and negative thermal expansion 1,2 , and also because of its giant negative linear compressibility 3 . The negative thermal expansion (NTE) along the c-axis and the positive thermal expansion (PTE) along the a(b) axes are an order of magnitude larger than that observed in many other crystalline solids.…”

Section: Introductionmentioning

confidence: 99%

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Ag–Ag dispersive interaction and physical properties ofAg3Co(CN)6

2014

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We report a density functional theory (DFT) study of Ag 3 Co(CN) 6 , a material noted for its colossal positive and negative thermal expansion, and its giant negative linear compressibility. Here we explicitly include the dispersive interaction within the DFT calculation, and find that it is essential to reproduce the ground state, the high-pressure phase, and the phonons of this material; and hence essential to understand this material's remarkable physical properties. New exotic properties are predicted. These include heat enhancement of the negative linear compressibility, a large reduction in the coefficient of thermal expansion on compression with change of sign of the mode Grüneisen parameters under pressure, and large softening of the material on heating. Our results suggest that these are associated with the weak Ag. . .Ag dispersive interactions acting with an efficient hinging mechanism in the framework structure.

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Phonons and colossal thermal expansion behavior of Ag₃Co(CN)₆and Ag₃Fe(CN)₆

Cited by 19 publications

References 35 publications

Negative thermal expansion in cubic ZrW2O8: Role of phonons in the entire Brillouin zone fromab initiocalculations

Negative thermal expansion in cubic ZrW2O8: Role of phonons in the entire Brillouin zone fromab initiocalculations

Uniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]

Ag–Ag dispersive interaction and physical properties ofAg3Co(CN)6

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