First Principles Study On The Physcial Properties Of Y₂O₃ Window-material Under High-pressure And Doping

Yttria transparent ceramics?Y₂O₃?has demonstrated the formidable vitality under high temperature and pressure.Because of its unique optical,mechanical,thermodynamic and other comprehensive performance,such as refractory high temperature and pressure,high hardness and strength,good ductility,excellent optical transparency and thermochemical stability and so on,and has become the most potential mid-wave infrared optical detection window materials.In this paper,the structural,electronic,optical,mechanical and thermodynamic properties of cubic Y₂O₃ crystals under La or Sc doping and hydrostatic pressures?0-14 GPa?and temperatures?0-2000 K?are systematically investigated,based on the first-principles plane wave pseudopotential method within density functional theory combined with the quasi-harmonic Debye model.To determine the ground state structure of Y₂O₃,we have use the CASTEP package,several different lattice parameter a are setted to calculate the total energy E corresponding primitive cell volume V.By fitting the calculated energy-volume?E-V?to the third-order Birch-Murnaghan equation of state?EOS?,we determined the equilibrium structure parameters?a₀,V₀?,the bulk modulus B₀ and its pressure derivative B₀',using LDA,GGA-PBE,and GGA+U approximations.The calculated elastic constants satisfied the stability certeria,indicating that the crystal structure of Y₂O₃ remains elastically stable in a pressure range from 0 to 14GPa,i.e.,it is still cubic.The bulk modulus,shear modulus,B/G,Young's modulus and Vickers hardness increase with the increase of pressure,which indicates that mechanical strength,hardness and toughness of Y₂O₃ becomes stronger as the pressure increases.The elastic anisotropy of Y₂O₃ is enhanced by the three-dimensional Young's modulus,elastic wave velocity and elastic anisotropy index.The thermodynamic properties of Y₂O₃ are determined in a temperature from 0 K to 2000 K and in a pressure from 0 GPa to 14 GPa by GIBBS program.The isothermal modulus B_T increases with increasing pressure and decreases with temperature,and the effect of pressure on isothermal modulus is more important than that of temperature.In addition,the heat capacity,thermal expansion coefficient and Grüneisen parameter decrease with increasing pressure and increase with temperature.The electronic and optical properties of Y₂O₃ were studied in detail in a pressure range from0 to14 GPa.It has been found that relative intensity of density of state on each section has a slight decrease when the pressure increases gradually,density of state of valence and conduction bands shift towards the low energy.The frontier band gaps are gradually decreasing and sapphire has metallicity tendency.The absorption coefficient,reflectance and optical transmittance of Y₂O₃ were calculated.The results show that the optical absorption and reflection are still concentrated mainly in the ultraviolet region,and there are almost no absorption and reflection at a range of wavelengths above 400 nm.The absorption peak and the reflection peak increase,the optical transmittance decreases,the optical absorption edge blue shift with the pressure.The analysis shows that Y₂O₃ keeps its transparency?more than81%?and translucent range up to 14 GPa at 0 K in the range of visible-infrared light wavelength.The electronic,mechanical and optical properties of La or Sc-doped Y₂O₃ are investigated by first-principle caculations.Two doping sites of Sc or La in Y₂O₃ system have been modeled.The calculated results of the formation of energy show that energy favorable site of La atom in Y₂O₃ is found to be on the d-site of Y atom.However,it is found that substitutional Sc_Y of b-site is more stable site.The calculated band gap shows a sligh decrease with increasing La or Sc concentration.However,we find that as pressure increases,the charge transfer and the bond length increases.The calculated results of the mechanical and optical properties of Y_2-xR_xO₃?R=Sc or La,0<x?0.1875?determined that the La or Sc-doped Y₂O₃ would be enhanced strength and the ability to resist external shocks,increased hardness and the mechanical toughness and hence improved mechanical properties without sacrificing optical transparency and translucent range.The theoretical calculated the mechanical and optical properties of Y_2-xR_xO₃?R=Sn or Y?provide theoretical guidance for Y₂O₃ as transparent window material.