Structure And Properties Of Diamond Powder Under High Pressure

The atoms in amorphous solid materials are randomly arranged(long-range disorder,short-range or medium-range order),which has the characteristics of isotropy,high hardness and high viscosity coefficient,and has attracted extensive research.Carbon atoms can be combined with each other in three hybrid forms of sp~1,sp~2 and sp~3,so there are many kinds of amorphous carbon,especially the amorphous carbon(a-C)materials formed by high proportion sp~3 bonding,whose hardness is equivalent to that of natural diamond,which makes the research of amorphous carbon materials become a hot topic.At present,most amorphous carbon research focuses on amorphous carbon thin film materials.Due to the large internal stress of amorphous carbon film,peeling will occur between the film and the substrate,which restricts the application of amorphous carbon film materials.The synthesis of amorphous carbon blocks under high pressure(HPHT)can effectively avoid the film peeling problem,but at present,the synthesis pressure of amorphous carbon with high proportion of sp~3 bonding is too high(more than 20 GPa),and the volume of the synthesized sample is small,which is not conducive to the testing and analysis of its physical properties.In this paper,translucent millimeter amorphous carbon was synthesized by using diamond powder as raw material,adding catalyst and high-pressure press with large cavity,and its structure and properties were characterized.The main results are as follows:(1)Red-brown translucent amorphous carbon blocks were synthesized under the pressure of 6 GPa and 10 GPa,respectively,and the geometric size reached 1 mm×2 mm.The structure and properties of the samples were tested by XRD,Raman and HRTEM.In HRTEM images of samples,not only amorphous phase,but also amorphous coated nanocrystals were found.(2)The ultraviolet-visible absorption test results of amorphous carbon samples show that its optical band gap is2.45 e V,which is close to the recent report on the band gap of amorphous carbon with high sp~3content(1.85-2.79 e V).(3)XPS test results show that there are a large number of sp~2 bonded carbon atoms in the sample,which is due to the residue of diamond powder after being converted into graphite at high temperature and high pressure,so it is necessary to further optimize the synthesis conditions and raw materials,so as to reduce the content of sp~2 bonded carbon atoms in the sample.(4)When no catalyst is added,transparent samples are not synthesized from diamond powder after high temperature and high pressure treatment.It shows the importance of adding catalyst to prepare and synthesize amorphous carbon materials at low pressure and temperature.In this paper,amorphous carbon materials were synthesized by using diamond powder at relatively low temperature and pressure,which provided a new research idea for preparing high proportion sp~3 bonded amorphous carbon blocks.