Study On Pressure-Induced New Phases And Propertiesof Fullerene Solvates: The Effect Of Intercalated Solvent

Development of new carbon materials with desired structures and properties is always an important topic in both PhysiCS and Material science fields.High pressure can effectively modulate the distances between atoms to affect the structure and electron distribution of materials,which is an important route to synthesis novel carbon materials with desirable structure and properties.Several breakthroughs in the high pressure studies on fullerene solvates have shown that the fullerene units undergo a pressure-induced amorphization transition to form a new long-range ordered amorphous carbon structure?OACC?with potential superhard property.This result not only expands the understanding of solid material structure form order to disorder,but also develops a new research field for carbon materials.At present,one of the key topic in this field is how to slect suitable solvent molecules to modulate the interactions between fullerene units under pressure for the creation of new carbon materials.It should be noted that the intercalated solvent molecules play important roles in the interaction and bond formation between the fullerene units,which is one of the key factors for the formation of the new high pressure carbon phase.However,the current researches are mainly focused on the fullerene solvates doped by aromatic solvent molecules,other solvent molecules doped solvateshave been scarcely studied and the understanding of the related mechanisms is still unclear.Therefore,a series of designed high pressure studies on fullerene solvates doped with suitable solvent molecules is of great significance for the development of carbon materials.In this paper,three kinds of solvent molecules,including mesitylene,CS₂?carbon disulfide?and C₈H₈?cubane?,were selected for synthesizing fullerene solvated crystals.High pressure studies have been carried out on these crystals.The roles of the spacing separation,doping concentration,structure and size and the reactivity of intercalated solvent molecules in modulating the structure and property transformations of the solvated crystals under high pressure have been revealed.The results of this paper are as follows:1.The photoluminescence?PL?property of C₇₀^*mesitylene solvated crystals was studied under pressure,which reveals the influence of the spacing separation effect of intercalated solvent molecules on the PL property of fullerene solvates.The maximum pressure in the experiment was 11 GPa.It was found that the rotational state of C₇₀ molecules had a significant effect on the PL properties of C₇₀^*mesitylene solvated crystals under pressure,but had little effect on pure C₇₀ crystals.The spacing separation effect of intercalated solvent molecules hinders the pressure enhanced C₇₀-C₇₀ interaction in the fullerene solvates,which leads to the PL property of solvated sample more sensitive to the change of the C₇₀ rotational state under pressure.These results help us to learn the influence of the spacing separation effect of intercalated solvent molecules on the PL property of fullerene solvates and discover new methods to tune the PL properties of fullerene solvated crystals.Meanwhile,the study deepens our understanding of the PL mechanisms of fullerenes and fullerene solvated crystals.2.We studied the influence of mesitylene solvent molecules on the structure and property transformation of C₇₀^*mesitylene solvated crystals(C₇₀:mesitylene=1:2)under pressure.The maximum pressure in the experiement was 46 GPa.It is found that the C₇₀^*mesitylene solvated crystals can transforminto OACC structure under pressure.The intercalated mesitylene solvent molecules act as “spacers” to play important roles in keeping the structure order of the solvated crystals under pressure.In contrast to m-xylene solvent molecueles,our results show that the mesitylene solvent molecules doped solvated crystals does not show any signs of superhardness,as indicated by the absence of cracks on diamond anvil surface.The comparative study shows that the high stability of mesitylene molecules and their Methly groups,and their high content in the solvated crystals may the important factors which result in the low mechanical property of the high pressure phase.These results help us to understand that the effect of the stoichiometric ratio of solvent molecules on the formation of the boundary between the fullerene clusters in solvated fullerene crystals under pressure.These results also provide us a new ideafor designing new carbon structure.3.High pressure infrared spectra measurement was carried on the C₆₀^*CS₂ solvates to 34.8G.It is found that the small size and linear structure CS₂ molecule can significantly promote the deformation of the C₆₀ molecule under pressure.In contrast,the aromatic solvent molecules have little influence on the deformation of C₆₀ and even can enhance their stability upon compression.On the other hand,the spacing separation effect of C₆₀ molecules dramatically enhances the stability of CS₂ molecules at high pressure.These results provide us new insight into the effect of the size and structure of interaclated molecules on the high pressure behavior of fullerene solvates.Furthermore,these results also provide us an idea to synthesize amorphous carbon clusters at a low pressure,which contributes to decrease the critical pressure for the transformation into OACC structure.4.The effects of the highly reactive C₈H₈ molecules on the transformations of C₆₀^*C₈H₈ crystal under pressure were investigated for the first time.It is found that the C₈H₈ molecules are highly compressed and start to deform above 10 GPa,which may lead to the polymerization between C₆₀ and C₈H₈.The highly compressed C₈H₈ can significantly enhance the stability of C₆₀ carbon cages and play an important role in keeping the lattice order of the sampleunder pressure,which enables the sample preserve its ordered structure up to 45 GPa.Interestingly,after a placement at high pressure,the sample was transformed into an amorphous phase with potentialsuperhardness.The results help us to understand the effect of the reactivity of the dopant solvent molecules on the structure and property transformation of solvated fullerenes under high pressure,and provide us a new method to synthesize new high pressure carbon phase with novel structures and properties.