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

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 I shows significant negative thermal expansion along its b axis, which can be explained by using a hinge-strut structural motif. (C) 2015 Elsevier Inc. All rights reserved.