Negative thermal expansion in framework structure materials

Near-room-temperature dielectric switch and thermal expansion anomaly in a new hybrid crystal: (Me2NH2)[CsFe(CN)5(NO)]

“…As shown in Fig. 4b, the NET occurring in the ab plane observed in the LTP should be ascribed to the vibration of cyano bridges in a displacement mode, 22,29 as indicated by the significant deviation of the cyano bridges (i.e., C1-N1, C2-N2, and C4-N4) from the linked lines of Fe⋯Cs (shown in dashed lines). For the HTP, all cyano bridges became closer to the linked lines of Fe⋯Cs (Fig.…”

Biaxial negative thermal expansion in Zn[N(CN)2]2

“…Since the report on the NTE of ZrW 2 O 8 in 1996, 4 NTE has been widely studied, and it has been observed in alloys, oxides, fluorides, nitrides, etc . 5,6 Notably, many of the framework structure materials also exhibit NTE properties driven by low-frequency phonons. Research on them is mainly focused on oxides, fluorides, cyanides and metal–organic frameworks (MOFs), like ZrW 2 O 8 , 4,7 ScF 3 , 8 Zn(CN) 2 , 9,10 and MOF-5.…”

Understanding Large Negative Thermal Expansion of NdFe(CN)6 through the Electronic Structure and Lattice Dynamics

“…Only rarely do some materials show a negative thermal expansion (NTE), and these play an important role since they make possible the realization of materials with zero thermal expansion (ZTE) or even better of materials with tailored thermal expansion . Accordingly, the NTE phenomenon has received great attention and rapid development, such that many NTE materials and mechanisms have been discovered, as reported in recent reviews. − Based on the NTE mechanism, the NTE materials can be grouped into two categories: − electron-driven NTE materials when the NTE is due to magnetic volume effect or charge transfer − and phonon-driven NTE when the presence of low-frequency phonon vibrations gives rise to NTE, ,,,, such as in some oxides, − fluorides, , cyanides, − and MOFs . Open-framework structure materials are excellent candidates for exhibiting phonon-driven NTE, whose origin is often related to the transverse thermal vibration by bridging atoms or the tilting and rotations of atomic polyhedral units.…”