Theoretical Calculation Research Of The Structure And Properties Of Binary Telluride Under High Pressure

Binary telluride materials have a very wide range of applications,and are widely used in the fields of thermoelectric materials,photoelectric detection,and phase change memory materials.For example,InTe and In₂Te₃ have very great application prospects in the field of photoelectric detection.Bi₂Te₃ is the best known and most widely used binary telluride material.The GeTe film is a very good binary telluride phase change memory material.Binary telluride is mainly used as a thin film material in terms of application.High-pressure technology can simulate the effect caused by lattice mismatch between the thin film and the substrate.In this thesis,the first-principles simulation calculation method is used to study the structure phase transition sequence and phase transition critical pressure of binary telluride.The evolutions of microstructures and properties under high pressure,i.e.,crystal unit parameters,geometric bond length,electron energy band structure,charge population have been investigated,in order to explore the internal microscopic mechanism of macroscopic crystal changes,and provide further theoretical support for the evolution of binary telluride under high pressure.In this thesis,several possible high-pressure phase structures of InTe crystals,i.e.TlSe-InTe?B37 type?,NaCl-InTe?B1 type?,CsCl-InTe?B2 type?,Sphalerite-InTe?B3?,Hg Mn-InTe and Pnma-InTe have been optimized for high-pressure structural relaxation from ambient pressure to 45 GPa.For the optimized enthalpy value of each structure,the enthalpy difference is calculated.InTe has two phase transition sequences under high pressure: Sequence one is that the B37 phase changes to the B1 phase at about 5 GPa,and the B1 phase changes to the Hg Mn phase at about 15 GPa,where the B1 phase is a metastable phase under high pressure;The second sequence is that the B37 phase can directly transform into the Hg Mn phase at about 25 GPa.The electronic structure that both the B37 and the Hg Mn phases are metallic in their respective pressure ranges.For ?-In₂Te₃,CN7M-In₂Te₃,CN8M-In₂Te₃,CN9M-In₂Te₃,BCT-In₂Te₃,high-pressure structure optimization from ambient pressure to 45 GPa was carried out.It is found that the ?-In₂Te₃ phase transforms into the BCT-In₂Te₃ phase at about 18 GPa,and the isostructural phase transition occurrs at about 9 GPa.By studying the electronic structure of the ?-In₂Te₃ and BCT phases,it is found that they both exhibit metallicity.The Bader effective charge and bond length for the ?-In₂Te₃ phase show that the structural phase change that occurred near 9 GPa is due to the occurrence of electronic topological transition.Finally,the crystal of Bi₂Te₃,Sb₂Te₃,and As₂Te₃ with tetradymite structure were optimized and calculated.It is found that an isostructural phase transition,which is caused by electronic topological transition,has happened in Bi₂Te₃ and As₂Te₃ at about 3 GPa and 8 GPa,respectively.At the pressures of the electronic topological transition,the electronic structures and bond lengths of Bi₂Te₃ and As₂Te₃ change discontinuously,and the morphology of the energy band structure near the Fermi surface in As₂Te₃ changes drastically.Compared with VA group tetradymite-type binary tellurides,?-In₂Te₃ has higher isostructural phase transition pressure,smaller axial ratio and volume compressibility,and smaller charge transfer capacity under high pressure.These differences between them may be caused by the different electronic configurations of the In and VA atoms.