ChemInform Abstract: Colossal Positive and Negative Thermal Expansion in the Framework Material Ag₃[Co(CN)₆].

Abstract

Ag 3 [Co(CN) 6 ]. -The thermal expansion behavior of the title compound is characterized by XRD over the temperature range from 16 to 500 K, neutron time-of-flight total scattering measurements at temperatures of 10, 50, 150, and 300 K, and DFT calculations. The material expands along one set of directions at a rate comparable to the most weakly bound solids known and shows negative thermal expansion along a perpendicular direction 14 times larger than in ZrW 2 O 8 . -(GOODWIN*, A. L.; CALLEJA, M.; CONTERIO, M. J.; DOVE, M. T.; EVANS, J. S. O.; KEEN, D. A.; PETERS, L.; TUCKER, M. G.; Sci. (Washington, D. C., USA) 319 (2008) 5864, 794-797; Dep. Earth Sci., Univ. Cambridge, Cambridge CB2 3EQ, UK; Eng.) -W. Pewestorf 18-006

Coexisting conventional and inverse mechanocaloric effects in ferroelectrics

“…Along the same lines, our perturbative theory plainly shows that the key to the predicted coexistence of conventional and inverse effects lies in the differentiated temperature dependence of the strains in the polar phase of PbTiO 3 : the strain parallel to the spontaneous polarization decreases upon heating, while the perpendicular strains increase. Interestingly, this feature is shared by many ferroelectrics [30][31][32]; and a similar anisotropic behavior of the strains is typical of compounds exhibiting a negative thermal expansion [26,33,34]. Thus, our analysis suggests that such compounds are likely to present a coexistence of conventional and inverse mechanocaloric responses.…”

“…Hence, the coexistence of conventional and inverse mechanocaloric responses may be a common feature among ferroelectrics. In addition, materials with a negative thermal expansion (where, often, some lattice constants decrease and some increase upon heating [26,33,34]) are also good candidates to present such a behavior.…”

Anomalous thermal expansion and chiral phonons in BiB3O6

“…1, bottom) [5]. By these standards, α-BiB 3 O 6 is an extraordinarily flexible inorganic material; it can be compared to the colossal NTE material Ag 3 [Co(CN) 6 ], for which Y max /Y min = 6.0 [16,17], and to ZnAu 2 (CN) 4 , which exhibits extreme NLC and has Y max /Y min = 3.8 [18].…”

“…Axial NTE has been studied extensively in the tetragonal, orthorhombic, and hexagonal crystal families due to the appearance of anomalously large-magnitude thermal expansion [17], connections with ferroelectricity [19,20], and the use of chemical control to achieve zero thermal expansion [21]. However, NTE is extremely rare in monoclinic and triclinic crystals [9,10] , with bismuth atoms coloured in magenta and borate units coloured in green [6].…”

Structure and Optical Properties of Layered Perovskite (MA)2PbI2–xBrx(SCN)2 (0 ≤ x < 1.6)

“…Thus, the molecular anion, SCN − , plays important a role for the linear expansion along the a axis. In some molecular complex materials, such as MIL-53 and Ag3[Co(CN)]6, 39,40 negative linear compressibility was reported by the so called 'wine-rack' mechanism; relative orientations of the molecular framework play a key role. 41 Although a negative linear compressibility was not reported in (MA)2PbI2(SCN)2, 16 the material having molecular ions, like the present compound, may be advantageous for seeking a compound with negative linear compressibility.…”