Departmental Papers (MSE)

Document Type

Journal Article

Date of this Version

8-20-2008

Abstract

Metal organic framework-5 (MOF-5)was recently suggested to possess an exceptionally large negative thermal-expansion coefficient. Our direct experimental measurement of the thermal expansion of MOF-5 using neutron powder diffraction, in the temperature range of 4 to 600 K, shows that the linear thermal-expansion coefficient is ≈−16×10−6 K−1. To understand the origin of this large negative thermal-expansion behavior, we performed first-principles lattice dynamics calculations. The calculated thermal-expansion coefficients within quasiharmonic approximation agree well with the experimental data. We found that almost all lowfrequency lattice vibrational modes (below ∼23 meV) involve the motion of the benzene rings and the ZnO4 clusters as rigid units and the carboxyl groups as bridges. These so-called “rigid-unit modes” exhibit various degrees of phonon softening (i.e., the vibrational energy decreases with contracting crystal lattice) and thus are directly responsible for the large negative thermal expansion in MOF-5. Initial efforts were made to observe the phonon softening experimentally.

Comments

Suggested Citation:
W. Zhou, H. Wu, T. Yildirim, J.R. Simpson, A.R. Hight Walker. (2008). "Origin of the exceptional negative thermal expansion in metal-organic framework-5 Zn4O(1,4-benzenedicarboxylate)3." Physical Review B. 78, 054114.

© 2008 The American Physical Society
http://dx.doi.org/10.1103/PhysRevB.78.054114

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Date Posted: 13 January 2011

This document has been peer reviewed.