Mechanical properties and negative thermal expansion of a dense rare earth formate framework

• The elastic modulus, hardness, and yield stress properties of a rare earth metal–organic framework material were studied via nanoindentation technique.
• Variable-temperature powder X-ray diffraction experiments reveal that this framework shows significant negative thermal expansion along its b axis.
• Based on variable-temperature single-crystal X-ray diffraction experiments, the mechanism of negative thermal expansion can be explained by a hinge–strut structural motif.

The fundamental mechanical properties of a dense metal–organic framework material, [NH2CHNH2][Er(HCOO)4] (1), have been studied using nanoindentation technique. The results demonstrate that the elastic moduli, hardnesses, and yield stresses on the (021)/(02−1) facets are 29.8/30.2, 1.80/1.83 and 0.93/1.01 GPa, respectively. Moreover, variable-temperature powder and single-crystal X-ray diffraction experiments reveal that framework 1 shows significant negative thermal expansion along its b axis, which can be explained by using a hinge–strut structural motif.

The structure of framework, [NH2CHNH2][Er(HCOO)4], and its indicatrix of thermal expansion.Figure optionsDownload as PowerPoint slide