SrHfO3和SrTiO3光学特性的第一性原理研究

用全电势线性缀加平面波法(FLAPW)计算了SrTiO₃和SrHfO₃的光学特性，即介电函数虚部ε₂(ω)、光学吸收系数I(ω)和反射率R(ω).对它们光学特性进行了对比分析，给出了它们光学特性的差别，并进行了解释.计算的SrTiO₃光学谱分别在4.4，7.4，8.3和23.6eV处出现峰值，且其在4.4eV处的峰值比较高而尖.计算结果与实验值符合得很好. 关键词： 平面波法计算 光学常量和参数 铁电体     

烧结温度对La0.9Sr0.1FeO3热电性能的影响

利用传统的固相反应分别在1250℃,1300℃,1350℃.烧结条件下制备出钙钛矿结构的La_0.9Sr_0.1FeO₃陶瓷样品.样品的XRD粉末衍射结果显示不同烧结温度的La_0.9Sr_0.1FeO₃陶瓷样品都是单相的正交结构,同时晶胞体积随着烧结温度的升高而减小.从样品的SEM结果看出,随着烧结温度的升高,晶粒逐渐变大,并且晶粒间的空隙逐渐减小,样品更加致密.在室温到800℃的 关键词： 铁酸镧陶瓷 热电性能 烧结温度     

聚偏氟乙烯全反式分子链振动模式的研究

利用ab initio分子轨道计算,对β相聚偏氟乙烯(PVDF)的全反式分子链进行了结构优化,计算值和实验值基本符合,且发现C－C－C键角有两种不同的值,112.8°和113.3°.对该分子的频率进行了计算,得到了红外强度谱.在400～4 000 cm-1范围内,对30 μm厚的聚偏氟乙烯取向膜和取向极化膜进行了红外光谱的测量，红外吸收光谱和红外强度谱基本一致.把所有振动模式分成六个系列:系列Ⅰ（544～415 cm-1）,系列Ⅱ（913～792 cm-1）,系列Ⅲ（1 353～998 cm-1）,系列Ⅳ（1 458～1 361 cm-1）,系列Ⅴ和系列Ⅵ.其中只有系列Ⅲ能改变分子的电偶极矩,该系列振动模式和β相的PVDF的自发极化有着密切的关系.     

Theoretical investigation of the thermoelectric transport properties of BaSi2

The full-potential linear augmented plane wave method based on density functional theory is employed to investigate the electronic structure of BaSi 2 . With the constant relaxation time and rigid band approximation,the electrical conductivity,Seebeck coefficient and figure of merit are calculated by using Boltzmann transport theory,further evaluated as a function of carrier concentration. We find that the Seebeck coefficient is more anisotropic than electrical conductivity. The figure of merit of BaSi 2 is predicted to be quite high at room temperature,implying that optimal doping may be an effective way to improve thermoelectric properties.     

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.     

SrTiO3中形成级联能级的理论分析

以Bi和Cu掺杂为例,通过基于密度泛函理论的电子结构的计算,分析了SrTiO₃体系中形成级联能级的可能性.结果表明,Bi掺杂和Cu掺杂都可以在SrTiO₃的禁带中引入杂质能带,Bi和Cu的共同掺杂可引入两条杂质能带.通过在两条杂质能带之间级联激发,价带顶的电子可以受激跃迁到导带底.采用无辐射跃迁的简单模型,分析指出电子通过级联激发从价带顶受激跃迁到导带底的概率远远高于直接从价带顶跃迁到导带底的概率.这种级联激发可以有效提高导带中的载流子浓度. 关键词： 级联能级 密度泛函 掺杂     

Thermoelectric properties of Li-doped Sr_(0.7)Ba_(0.3)Nb_2O_(6-δ) ceramics

Thermoelectric properties of Li-dopedSr_(0.7)Ba_(0.3)Nb_2O_(6-δ)ceramics were investigated in the temperature range from 323 K to 1073 K. The electrical conductivity increases significantly after lithium interstitial doping. However, both of the magnitudes of Seebeck coefficient and electrical conductivity vary non-monotonically but synchronously with the doping contents, indicating that doped lithium ions may not be fully ionized and oxygen vacancy may also contribute to carriers. The lattice thermal conductivity increases firstly and then decreases as the doping content increases, which is affected by competing factors.Thermoelectric performance is enhanced by lithium interstitial doping due to the increase of the power factor and the thermoelectric figure of merit reaches maximum value(0.21 at 1073 K) in the sample Sr_(0.70)Ba_(0.30)Li_(0.10)Nb_2O_6.     

Effect of trifluoroethylene monomers on molecular conformation of poly（vinylidene fluoride-trifluoroethylene） copolymer

Hartree－Fock and density functional theory (DFT) methods were employed to study poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains with different VDF contents. The dependence of dipole moment of P(VDF-TrFE) chains on VDF content obtained from our calculation is in good agreement with the experiment. The TrFE monomer plays an important role in introducing the gauche bond into copolymer chains. A possible mechanism was interpreted.