High Pressure Study On Zero Linear Compressibility Of Metal-organic Frameworks MIL-122 (In,Ga)

Under normal circumstances,when a substance is subjected to external hydrostatic pressure,its unit cell will shrink in all directions,that is,positive compression.However,some substances will remain unchanged in a certain direction under the continuously increasing hydrostatic pressure,or even elongate,that is,zero compression/negative compression occurs.This kind of phenomenon is called abnormal compression behavior of the substance.Nowadays,there is a few research on the phenomenon of zero compression,but its potential application is very wide.Because of its excellent structural stability,the ZLC materials are not susceptible to pressure fluctuations in the external environment,and will play a role in many fields in the future,such as the manufacture of precision instruments,collision protection equipment and submarine communication optical fibers.The metal ions and organic ligands of metal organic framework(MOFs)materials are combined by coordination bonds to form an organic-inorganic hybrid material with intramolecular voids.The appearance of large voids makes this type of material considered to be a representative of good flexibility structural materials.More and more experiments have shown that MOFs can be induced structural changes through external stimuli,such as changes in temperature or interaction with light,and produce different structural evolutions.Pressure,as another variable in physics that is different from temperature,can directly control the structure of matter.The use of modern high-pressure scientific experimental techniques to conduct high-pressure research on MOFs materials can provide research ideas for exploring more and more abundant materials'abnormal structure evolution.Using high-pressure synchrotron radiation X-ray diffraction experiments,we found the MOFs material MIL-122(In)with zero linear compression rate K_a=-0.27 TPa^-1,and the pressure range of zero linear compression phenomenon is excellent(1 atm?10.5 GPa).The abnormal mechanical response of MIL-122(In)to the effect of pressure can be attributed to its special wine rack topology.We abstracted the side length r and the articulation angle?in the rhombus structural unit from the actual structure.The competitive relationship between r and?dominate the evolution of the rhomboid structural unit in different pressure ranges,and finally reflects the zero linear compression phenomenon.In order to verify this peculiar phenomenon and the combination of its hinged atoms and organic ligands is not a special case,we conducted the same test on the MOF material MIL-122(Ga),and the result shows its linear compressibility is Ka=-0.83TPa^-1.The pressure range of zero linear compressibility phenomenon is 1atm?8.25 GPa,indicating that this structure can still exhibit zero linear compressibility after replacing the hinged atoms.But the performance of zero linear compressibity is slightly inferior to MIL-122(In).This paper uses the high-pressure in-situ synchrotron radiation X-ray diffraction technology and first-principles calculations to provide an example of zero linear compressibility:MOF materials can exhibit good linear stability through special topological responses of wine racks.Explore or design zero-compression materials in the future to provide experimental basis.