Correlation between Uniaxial Negative Thermal Expansion and Negative Linear Compressibility in Ag₃[Co(CN)₆]

Abstract

Density functional theory (DFT) calculations are used to investigate the correlation between the uniaxial negative thermal expansion (NTE) and negative linear compressibility (NLC) behaviors in Ag3[Co­(CN)6]. First, we reproduce the uniaxial-NTE and NLC behaviors under temperature- and pressure-field. And then the temperature dependence of elasticity is studied. The abnormal nature of elastic constants C 33 and C 11+C 12 as the function of temperature is predicted. The hardening of phonon modes (below 568.7 cm–1) with increasing temperature can be as an indicative for abnormal physical properties of Ag3[Co­(CN)6]. Through analyzing the vibration mode with the strongest phonon hardening, the deformation of wine-rack motif in anisotropic framework can be identified as the mechanism that leads to the coexistence of uniaxial-NTE and NLC in Ag3[Co­(CN)6]. The response of phonon group velocity along c-axis is intense and quicker than that of a-axis on heating and on compression, facilitating c-axis itself to be the carrier of abnormal uniaxial-NTE and NLC properties.

Synthesis, PtS-type structure, and anomalous mechanics of the Cd(CN)2 precursor Cd(NH3)2[Cd(CN)4]

“…1,5 3.4 Ab initio calculation of elastic properties NTE materials often exhibit a range of other anomalous mechanical and elastic responses: the geometric mechanism responsible for NTE usually also dominates the material response to strain or pressure. 56,57 In the case of Cd(NH 3 ) 2 [Cd(CN) 4 ], for exam- ple, its wine-rack NTE mechanism couples contraction along the c axis to an increase in molar volume (note α V > 0 in Table 2), and so the application of hydrostatic pressure-which requires volume reduction-ought to drive to an expansion in c. Such expansion-under-pressure is termed negative linear compressibility (NLC) and remains a relatively rare and attractive materials property. 58 PtS itself is thought to exhibit NLC, 59 and we conclude our study by attempting to answer the simple question of whether Cd(NH 3 ) 2 [Cd(CN) 4 ] also exhibits NLC and/or any other anomalous elastic responses.…”

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].…”

“…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].…”

Synthesis, PtS-Type Structure, and Anomalous Mechanics of the Cd(CN)2 Precursor Cd(NH3)2[Cd(CN)4]

“…NTE materials often exhibit a range of other anomalous mechanical and elastic responses: the geometric mechanism responsible for NTE usually also dominates the material response to strain or pressure. 51,52 In the case of Cd(NH 3 ) 2 [Cd(CN) 4 ], for example, its wine-rack NTE mechanism couples contraction along the c axis to an increase in molar volume (note α V > 0 in Table 2), and so the application of hydrostatic pressure-which requires volume reduction-ought to drive to an expansion in c. Such expansion-under-pressure is termed negative linear compressibility (NLC) and remains a relatively rare and attractive materials property. 53 PtS itself is thought to exhibit NLC, 54 and we conclude our study by attempting to answer the simple question of whether Cd(NH 3 ) 2 [Cd(CN) 4 ] also exhibits NLC and/or any other anomalous elastic responses.…”