First Principles Investigations Of The Optoelectronic Properties Of Doped ?-Ga₂O₃ And The Mechanics Properties Of Rhodium Based Alloy

In this work,the first principles based on density functional theory was applied to study systematically the photoelectrical properties of Nb-doped ?-Ga₂O₃,and the structural,electronic,elastic and some important thermodynamic properties of rhodium alloy?Rh₃Nb and Rh₃Sc?under high pressure.Firstly,the structural and optoelectronic properties of Nb-doped ?-Ga₂O₃ has been studied by the first principles with in the pseudo-potential plane wave method.The structural properties show that the calculated lattice parameters and cell volume were in good agreement with available experimental and theoretical results and greater than the intrinsic ?-Ga₂O₃.The result of formation energy shows that Nb is more inclined to replaced the Ga?B?atom at the octahedral site resulting in NbGa?B?-Ga₂O₃.The band structure shows that intrinsic ?-Ga₂O₃ and Ga1.875Nb0.125O3 are direct gap semiconductor and the forbidden band width is reduced after doping.The density of states?DOS?show that the total state density?TDOS?of Nb doped ?-Ga₂O₃ shift to low energy region.The calculated optical properties of intrinsic ?-Ga₂O₃ and Ga1.875Nb0.125O3 illustrate that the imaginary parts of the dielectric function ?2???,photochemical absorption edge,reflectivity peak and energy loss peak are slightly red-shifted,which indicates that Nb-doped ?-Ga₂O₃ can obtain higher energy from solar and increase the plasma resonance frequency.Secondly,the effects of pressure?0⁴5 GPa?on the structural,electronic,elastic properties and Debye temperature??D?of Rh₃Nb are investigated by the first-principles calculations.The calculated lattice parameters and volume reduce gradually with the increasing pressures.The density of states?DOS?reveal that Rh₃Nb has metallic character at zero pressure and has no phase transition with the rising of pressure up to 40 GPa.The difference charge density and the Mulliken charge indicate that the Rh₃Nb is composed of ionic bond and covalent bond.The values of elastic constants Cij show that Rh₃Nb fulfilled the mechanical stability criteria.Elastic modulus?bulk modulus B,shear modulus G,Young modulus E?and Debye temperature??D?increase linearly along with the pressure.Lastly,the density functional theory and the quasi-harmonic Debye model are used to investigate the structural,electronic,elastic and thermodynamic properties of Rh₃Sc compound under high pressure?0⁵0 GPa?and temperature?0¹500 K?ranges.The calculated lattice parameter of Rh₃Sc compound at 0 GPa is in good agreement with the available experimental value.The calculated total density of states at various pressures,0 GPa,25 GPa and 50 GPa,show that the stability of Rh₃Sc compound increases with increasing pressure.The pressure dependence on the elastic constants Cij,elastic modulus?B,G,E?were also calculated successfully.B/G ratio and Poisson ratio ? reveal that Rh₃Sc exhibits a ductility characteristic at zero pressure,and has the better the ductility with the increase of pressure.Finally,the temperature and pressure variation of the thermal expansion ?,heat capacity CV and Debye temperature ? are also calculated in a wide pressure?0⁵0 GPa?and temperature?0¹500 K?ranges and discussed.