Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion. Metal-Organic Framework (MOF) with unique structure flexibility is ideal material to study the thermal expansion. This work adopts the high-resolution variable-temperature powder X-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF ([Sr(DMPhH2IDC)2]n). It has the unique honeycomb structure with 1D channels along c-axis direction, the a-b plane displays layer structure. The thermal expansion behavior has strong relationship with the structure, ZTE appears in the a-b plane and large PTE along c-axis direction. The possible mechanism is that the a/b layers have enough space for the transverse thermal vibration of polydentate ligands, while along the c-axis direction is not. This work not only reports one interesting zero thermal expansion material, but also provides new understand for thermal expansion mechanism from the perspective of structural model.
A large negative thermal expansion
(NTE) (αv =
−4.1 × 10–5 K–1, 100–525
K) has been discovered in NdFe(CN)6. Here, the synchrotron
X-ray diffraction and lattice dynamics calculations using the density
functional theory were conducted to understand the NTE in NdFe(CN)6. The information obtained on the bond nature of the Nd–NC–Fe
linkage and on the atomic thermal vibrations suggests that the transverse
vibrations of the −NC– group, in particular
from N atoms, produced the NTE in NdFe(CN)6. This is corroborated
by the calculated Grüneisen parameters, which confirm the relationship
between NTE and CN atomic vibrations. The results provide a helpful
contribution toward the realization of new materials with negative
or controllable thermal expansion.
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