First-Principles Study of Electronic and Optical Properties of Y1-xCaxTiO3 （x=0, 0.25, 0.5, 0.75）

The full potential linearized augmented plane wave （FP-LAPW） method with the generalized gradient approximation （GGA） is applied to study the electronic and optical properties of perovskite-type compounds Y1-xCaxTiO3. The lattice parameters, magnetic moment, band structure, density of states and optical conductivity are obtained. The results show that the Ca ion plays an important role in the electronic properties and optical responses. Moreover, the optical properties including the dielectric function, absorption spectrum, extinction coefficient, energy-loss spectrum and refractive index are also discussed.     

Electronic structures and optical properties of TiO2:Improved density-functional-theory investigation

TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha＇s modified Becke-Johnson（TB-mBJ） exchange potential（plus a local density approximation correlation potential） within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation（LDA） and generalized gradient approximation（GGA）,in contrast with substantially overestimated values from many-body perturbation（GW） calculations.As for optical dielectric functions（both real and imaginary parts）,refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.     

Electronic structures and optical properties of TiO₂:Improved density-functional-theory investigation

TiO2 has been recently used to realize high-temperature ferromagnetic semiconductors.In fact,it has been widely used for a long time as white pigment and sunscreen because of its whiteness,high refractive index,and excellent optical properties.However,its electronic structures and the related properties have not been satisfactorily understood.Here,we use Tran and Blaha’s modified Becke-Johnson(TB-mBJ) exchange potential(plus a local density approximation correlation potential) within the density functional theory to investigate electronic structures and optical properties of rutile and anatase TiO2.Our comparative calculations show that the energy gaps obtained from mBJ method agree better with the experimental results than that obtained from local density approximation(LDA) and generalized gradient approximation(GGA),in contrast with substantially overestimated values from many-body perturbation(GW) calculations.As for optical dielectric functions(both real and imaginary parts),refractive index,and extinction coefficients as functions of photon energy,our mBJ calculated results are in excellent agreement with the experimental curves.Our further analysis reveals that these excellent improvements are achieved because mBJ potential describes accurately the energy levels of Ti 3d states.These results should be helpful to understand the high temperature ferromagnetism in doped TiO2.This approach can be used as a standard to understand electronic structures and the related properties of such materials as TiO2.     

Sr0.75Ba0.25Nb2O6薄膜的PLD制备及其光学性能研究

本文采用脉冲激光沉积(PLD)方法在熔石英衬底上制备了Sr0.75Ba0.25Nb2O6(SBN0.75)光波导薄膜,采用Hitachi U-3410紫外-可见分光光度计对SBN0.75薄膜的透射谱进行测量,编程计算得到了薄膜折射率色散关系,同时得到SBN0.75薄膜的厚度和光学带隙分别为647.0nm和3.97eV。采用Metricon 2010棱镜耦合仪测量得到SBN0.75光波导薄膜中能激发的TE模式有4个,TM模式有3个。波长在632.8nm处薄膜的折射率为2.2818。并利用透射谱计算得出的薄膜的折射率和厚度值,根据波导理论导光模本征值的有效折射率表达式,对SBN0.75薄膜中能激发的导光模个数及其对应有效折射率进行图解,其结果与棱镜耦合仪所测得的结果非常吻合。