Synthesis Of Gd-doped And Mg-doped Diamonds Under High Pressure And High Temperature

Carbon is an element with extremely versatile bonding properties,which can form isomeric carbon skeletons of different dimensions with different bonding method.The combination of metallic elements and carbon skeleton can produce new metal organic compounds with unique structure and properties.High-pressure and high-temperature（HPHT）experiment is an important technique for synthesize new metal organic compounds.Pressure and temperature are two important parameters in the thermodynamic which can change the structure and properties of the materials.High pressure decreases the distance between atoms that enhance the chemical reaction activity.Unsaturated carbon-carbon bonds polymerize under high pressure,and pressure induced polymerization（PIP）has the advantages of controllable,designable and higher conversion rates than conventional polymerization reaction,therefore,it can be used to enhance the saturation of unsaturated metal-carbon skeleton materials and synthesize new metal organic compounds.High temperature provides additional energy for the generation of new phase that obtain new metal organic compounds with high hardness and density which are difficult to synthesize at ambient temperature and pressure.In this paper,we focused on endohedral metallofullerenes（EMFs）Gd@C₈₂and dicyclopentadienyl magnesium typical metal organic compound with unsaturated organic groups.In-situ Raman spectra,Infrared spectra and X-ray diffraction（XRD）show the phase transformation and the pressure of polymerization reaction.Based on the above research work,we also synthesized metal-doped diamond in 6-8 multi-anvil press（MAP）by these two compounds and investigated the properties and structure of HPHT products,The main research results obtained are as follow:1.Gd-doped diamond was synthesized under HPHT condition using MAP with Gd@C₈₂as precursor compound.The polymerization reaction pressure of Gd@C₈₂is around 13 GPa（1 GPa=10000 atm）.The metal is still ordered in the carbon skeleton at higher pressure,therefore,We synthesized Gd-doped diamond at HPHT using Gd@C₈₂polymerization phase as precursor.Lattice of Gd-doped diamond synthesized at 22 GPa enlarged by 2%and grain size decreases significantly.This phenomenon did not occur in the experiment using C₆₀as the control group,which indicates Gd doped into the diamond lattice.The magnetic test results show that the Gd-doped diamond is paramagnetic,which is related to the Gd element doping.2.The polymerization reaction of dicyclopentadienyl magnesium under HPHT was studied,which provides an important reference for the synthesis of doped diamond using metal-organic compounds as precursor.The fist order phase transition of dicyclopentadienyl magnesium occurs at around 2.5 GPa and polymerization reaction occurs at around 20 GPa.The PIP reaction follows the cycloaddition reaction mechanism,and only（C₅H₅）_ncan be observed on the chromatography after the hydrolysis of polymerization products.Metal magnesium is still partially ordered in the organic carbon skeleton under polymerization pressure.Based on the results of the above study,we determined that dicyclopentadienyl magnesium transforms to diamond at 22 GPa and 1700℃.