3, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
2, Institute of High Performance Computing, Singapore, , Singapore
Organic and organic-inorganic hybrid piezo/ferro-electric materials have been burgeoning recently for their low densities, high flexibilities, and solution processibilities. Despite the successive observations of the physical piezo/ferro-electric phenomena in some organic and organic-inorganic materials, this prospect is still not good-fetched yet. The goal of this work is to unravel the structural functionalities within natural biomacromolecules and artificially formed metal-organic frameworks (MOFs) and to offer a strategy for constructing promising supramolecular piezo/ferro-electric materials. On one hand, our nanoscale probing as well as theoretical calculations indicate that the piezoresponses of collagen fibrils in wild mice bone is larger than those in genetic modified osteogenesis imperfecta murine (OIM) mice bone via delicate dual AC resonance tracking piezoresponse force microscopy (DART-PFM) characterizations and molecular dynamics simulations respectively. We thereby describe the better piezoelectricity by forming heterotrimeric peptide chains comprising polar residues within the oriented structure of collagen biomacromolecules. On the other hand, we have experimentally found that both the NUS-6 and UiO-66 MOFs nanocrystals demonstrate certain piezoelectricity. Besides, the Hafnium (Hf)-based MOFs show better ferroelectricity than their counterparts zirconium (Zr)-based MOFs nanocrystals. These findings evident the low symmetric lattice structure in real NUS-6 and UiO-66 MOFs. To unravel the underlying mechanism, first principles density functional theory (DFT) calculations have been performed on the UiO-66 MOFs with FCC crystal structures (F-43m, 216). It is found that the Born effective charges as well as the polarization changes of atoms in UiO-66 (Hf) are larger than those in the UiO-66 (Zr). Herein, we propose the ferroelectricity of MOFs could be tunable by judicious selection of metal ions to form more polar coordination bond and capable of forming electronic structure in asymmetric lattice. Through both experimental and theoretical simulation, we demonstrate the piezo-/ferro-electricity phenomena in supramolecular materials.