High Temperature And High Pressure Synthesis Of New Black Phosphorus-based Materials And Research On Physical Properties Under Extreme Conditions

Since the discovery of two-dimensional materials,researchers have been interested in them,and many of their physical and chemical properties are worth our attention.Graphene was first successfully prepared in 2004 and has shown excellent properties in the fields of mechanics,heat,electricity and optics.Although graphene has high electron migration,due to its characteristic of zero band gap,it cannot express circuit"ON"or"OFF",which seriously restricts its applications in electronics,thermoelectricity,optoelectronics and other fields.In order to solve these problems,black phosphorus(BP),as a new two-dimensional material,comes into our horizon.In our previous studies,we found that strong thermal and electrical anisotropy in the layer BP,it has a great potential to become a new thermoelectric material in a specific direction.However,the practical application of BP material still has such technical problems,poor stability,difficulty in preparing large-size single crystal and the one-dimensional material growth,which seriously limits its application value in the field of new functional materials.In this paper,the layered black phosphorus based semiconductor materials(BP,germanium phosphide(GeP₅))to achieve the synthesis of large size single crystal and a new type of composite material,relying on high temperature and high pressure technology,using the diamond anvil cell(DAC)technology to study the structure and physical properties of GeP₅ under high pressure.The specific research content is carried out from the following aspects:(1)In view of the difficulties of one-dimensional structure BP materials in the field of material science,in this work,we successfully prepared"quasi-one-dimensional"BP matrix composites for the first time in the world by means of vacuum sealing,high temperature and high pressure preparation,combined with heteroepitaxial growth technology.We selected with high stability,broadband gap structure of one-dimensional hexagonal boron nitride(h–BN)nanotubes as base,high pure red phosphorus(RP,99.999 wt%)as starting material,first through the sealing method,in the vacuum condition to gasification RP attached to the h–BNNTs on the surface,by controlling the raw material doping ratio can achieve its surface layer thickness control;Secondly,the RP layer attached on the surface was transformed into BP structure at 2 GPa and1270-1470 K by the cubic press apparatus.Finally,the"quasi-one-dimensional"BP/h-BN composite material was successfully prepared by high resolution Raman diffraction,XRD diffraction,electron spectroscopy,scanning electron microscopy and transmission electron microscopy.The diameter,length and thickness of the one-dimensional BP/h-BN composite prepared by this work can be adjusted according to the size of substrate and the ratio of original material.Because the surface suspended bond which seriously affects the stability of BP is bound by the boron on the surface of h-BN,its oxidation resistance and thermal stability in the air are significantly improved.In addition,because h-BN is an excellent insulating material,the conductive properties of the BP/h-BN composite come from the BP layer on the surface,so it is high adjustable,which makes it have a wide range of application prospects.We found that the structure has higher potential thermoelectric conversion efficiency than the pure one-dimensional BP structure.So far,this is the first time that"quasi-one-dimensional"BP-based material to be realized in the field.These excellent properties and preparation technology can also be extended to BP based one-dimensional materials and composites with similar structures,thus offering a new option for design of high-performance flexible green thermoelectric materials.(2)GeP₅ is a new 2D material with"black phosphorus like"structure.Compared with BP,GeP₅ has higher stability and superior electrical conductivity,and its conductivity can reach 10 times more than graphite.Therefore,GeP₅shows great potential in the new functional materials such as supercapacitors and thermoelectric conversion.At this stage,people use high-energy ball milling technology to prepare nanoscale samples.So,the preparation and physical properties of large-size single crystals have great significance for their practical application.High temperature and high pressure technology has unique advantages in preparing large 2D single crystal.Therefore,in this work,we successfully prepared high quality,centimeter-level GeP₅ single crystal by using a cubic press apparatus at2.5 GPa and 1200?.Furthermore,using diamond anvil cell technology,combined with in-situ Raman,electric transport test,synchrotron radiation XRD and magnetic test,the physical properties of GeP₅ under extreme conditions were investigated.A structural phase transition from 2D to 3D at 13.5 GPa was first observed in GeP₅ single crystal.Along with the phase transition,GeP₅ single crystal under high pressure shows different properties from other reported 2D materials.Including Raman spectra under high pressure(60 GPa)shows that the phonon softening of GeP₅.The stability of superconductivity under the high pressure was shown,the superconducting starts at 2.5GPa,achieve the highest superconducting temperature 10.5 K at 13.5 GPa,then the superconducting temperature steadily to 60 GPa,no obvious decline trend.By theoretical simulation and structural analysis of the pressed samples by using high resolution transmission electron microscopy(HRTEM),it is found that the phonon softening and stable superconducting properties of GeP₅ are caused by the nesting of Fermi levels in the GeP₅ structure and the structural amorphism under high pressure.