First-principles Study On The Regulation Of Optical And Electrical Properties Of Barium Titanate

As an important functional material,ferro-voltage electroceramics have a wide range of applications in industrial production and daily life,mainly used in electronic components such as sensors,resonators,and transducers.At present,lead-containing ceramics such as lead zirconate titanate and lead niobium magnesium acid occupy the main share of the market,but ceramics containing a large amount of lead elements will cause great harm to human health and the natural environment after use.Therefore,in addition to restricting the use of lead-containing ceramic materials,it is necessary to explore lead-free piezoelectric ceramics that are friendly to the environment and human health.Lead-free BaTiO₃（BT）ceramics have attracted much attention for their low cost,chemical stability and simple preparation process.However,the commercial application of BT ceramics is affected by factors such as low Curie temperature and small dielectric constant.Fortunately,the researchers found that doping can regulate the optical and electrical properties of BT ceramics,which provides an effective way to improve the performance of lead-free piezoelectric ceramics.In this paper,the model construction of BT system is completed with the help of Materials Studio software,and the optical and electrical properties of Ca atom-doped BT system（BCT）,Zr atom-doped BT system（BZT）and Ca-Zr co-doped BT system（BCZT）are calculated by using density functional theory,and the effects of different proportions of dopants on the piezoelectric performance of BT system are also calculated.In addition,pure 2D BT systems and doped 2D BT systems were constructed,and optical and electrical properties were calculated and analyzed.The first-principles calculation results show that the BCT system decreases in volume because the Ca atomic radius is less than the Ba atomic radius,the BZT system increases in volume because the Zr atomic radius is greater than the Ti radius,and the BCZT system changes from a tetragonal structure to a cubic structure,and the lattice parameters are consistent with the experimental results.Ca doping,Zr doping and Ca/Zr co-doping increased the band gap of the BT system.In addition,the band gap value of HSE06 functional calculation is consistent with the experimental report,while the band gap value of GGA functional and LDA functional calculation is significantly lower than the experimental value.Doping can improve the ferroelectric properties of the BT system,and the ferrous polarization value of the BCZT system is increased by150%compared with the BT system.Studies of optical properties,Debye temperature and elastic properties show that the refractive index of BCZT system decreases,thermal conductivity decreases,and anisotropy index increases.In addition,the co-doping of Ca and Zr increased the piezoelectric strain tensor d₃₃ of the BT system by about 125%,and the doped BT system was more than 4 times when the content of Ca was 0.15and the content of Zr was 0.1.The results of the study of pure 2D BT system and doped 2D BT system show that after optimization,the lattice constant of 2D BCT,2D BZT and 2D BCZT systems increases,which is due to the absence of interatomic interaction force on the c-axis and the defective structure formed by doped atoms.The band gap value of the 2D BT system was1.732 e V using GGA functional calculation,while the band gap values of2D BCT,2D BZT and 2D BCZT were 1.752 e V,2.158 e V and 2.246 e V,respectively.In terms of optics,the four systems are optical isotropic,and in terms of mechanics,doping can enhance the plastic deformation ability of 2D BT systems.The calculated value of the piezoelectric coefficient e₁₁ of the 2D BT system is 0.34×10^-10 C/m,the piezoelectric coefficient of the 2D BCT system decreases,the piezoelectric coefficient of the 2D BZT increases,and the value of the piezoelectric coefficient e₁₁ of the 2D BCZT system is as high as 1.32×10^-10 C/m,which is 3.8 times higher than that of the 2D BT system.The results show that the optical,ferroelectric and piezoelectric properties of the BT system can be regulated by doping strategy,it has certain reference value and guiding significance for experimental research on the optical and electrical properties of BT system.