Electronic Structure and Optical Properties of La-Doped SrTiO3 and Sr2TiO4 by Density Function Theory

The effect of La doping on the electronic structure and optical properties of SrTiO₃ and Sr₂TiO₄ is investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory (DFT). The calculated results reveal that the electron doping in the case of Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ can be described within the rigid band model. The La³⁺ ions fully acts as electron donors in Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ systems and the Fermi level shifts further into the conduction bands (CBs) for Sr_1.875La_0.125TiO₄ compared to Sr_0.875La_0.125TiO₃. The two systems exhibit n-type degenerate semiconductor features. At the same time, the density of states (DOS) of the two systems shift towards low energies and the optical band gaps are broadened. The Sr_1.875La_0.125TiO₄ is highly transparent with the transmittance about 90% in the visible range, which is larger than that of Sr_0.875La_0.125TiO₃(85%). The wide band gap, small transition probability and weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the optical transparency of the films...     

Electronic structure and optical properties of Nb-doped Sr2TiO4 by density function theory calculation

This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory(DFT).The calculated results reveal that due to the electron doping,the Fermi level shifts into conduction bands(CBs) for Sr2 Nb x Ti1 x O4 with x=0.125 and the system shows n-type degenerate semiconductor features.Sr2TiO4 exhibits optical anisotropy in its main crystal axes,and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region.The optical transmittance is higher than 90% in the visible range for Sr2 Nb 0.125Ti0.875O4.     

Effect of In-Doping on Electronic Structure and Optical Properties of Sr2TiO4

The effect of In doping on the electronic structure and optical properties of Sr2 TiO4 is investigated by a firstprinciples calculation of plane wave ultrasoft pseudopotentials based on density functional theory. The calculated results reveal that corner-shared TiO6 octahedra dominate the main electronic properties of Sr2TiO4 and the covalency of the Ti-O（1） bond in the ab plane is stronger than that of the Ti-O（2） bond along the c-axis. After In doping, there is a little lattice expansion in Sr2In0.125 Ti0.875 O4 and the interaction between the Ti-O bond near the impurity In atom is weakened. The binding energies of Sr2TiO4 and Sr2In0.125Ti0.875O4 estimated from the electronic structure calculations indicate that the crystal structure of Sr2In0.125 Ti0.875 O4 is still stable after doping, but its stability is lower than that of undoped Sr2TiO4. Moreover, the valence bands （VBs） of the Sr2In0.125Ti0.875O4 system consist of O 2p and In 4d states, and the mixing of O 2p and In 4d states makes the top VBs shift significantly to high energies, resulting in visible light absorption. The adsorption of visible light is of practical importance for the application of St2 TiO4 as a photocatalyst.     

Y掺杂SrTiO3晶体材料的电子结构计算

采用基于第一性原理的密度泛函理论平面波超软赝势法, 研究了Y掺杂SrTiO₃体系的空间结构和电子结构性质, 得到了优化后体系的结构参数, 掺杂形成能, 能带结构和电子态密度. 对比掺杂浓度为0125, 025, 033时,Sr_1-xY_xTiO₃和SrTi_1-xY_xO₃的掺杂形成能,发现Y替代Sr能形成更稳定的结构. 对Sr_1-xY_xTiO₃（x=0, 0125, 025, 033） 的结构进行了优化,结果表明Y替代Sr后, 随着掺杂浓度增大, 体系的晶格常数逐渐减小, 稳定性逐渐增强. 对不同掺杂浓度的Sr_1-xY_xTiO₃能带结构的计算结果表明：纯净的SrTiO₃是绝缘体, 价带顶在R点, 导带底在Γ点, 费米能级处于价带顶; 掺杂Y后, 费米能级进入到导带底中, 体系呈金属性;掺杂浓度越大,费米能级进入导带的位置越深,禁带宽度也近似变宽. 关键词： 3')" href="#">SrTiO₃ 电子结构 掺杂 VASP     

Magnéli相亚氧化钛Ti8O15的电子结构和光学性能的第一性原理研究

采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti₈O₁₅的电子结构和光学性能. 计算出的能带结构显示Ti₈O₁₅相比锐钛型TiO₂禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti₈O₁₅的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO₂的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO₂, Ti₈O₁₅ Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO₂仅在紫外光区有较高的光吸收能力, 而Ti₈O₁₅由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致. 关键词： 第一性原理 8O₁₅')" href="#">Magnéli相亚氧化钛Ti₈O₁₅ 电子结构 光学性能     

Adsorption of CO, NH3 and O2 on Fe site of La0.875Sr0.125FeO3 (0 1 0) surface by density function theory calculation

The adsorption of CO, NH₃ and O₂ gas molecules on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface has been investigated based on the density functional theory (DFT) with the spin polarized generalized gradient approximation (GGA). The optimal adsorption orientations as well as the adsorption energies for these molecules adsorption on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface are derived. Results show that adsorption configurations with C-down for CO, N-down for NH₃ are stable. For the O₂ molecule adsorption, the mode with an angle about 120° between the oxygen molecule and La_0.875Sr_0.125FeO₃ (0 1 0) surface is stable.     

(Bi,La)4Ti3O12-Sr(Bi,La)4Ti4O15共生结构铁电材料性能研究

采用固相烧结工艺，制备了不同La掺杂量(x=0.00，0.25，0.50，0.75，1.00，1.25和1.50) 的(Bi, La)₄Ti₃O₁₂-Sr(Bi, La)₄Ti4O₁₅ (SrBi_8-xLa_xT i₇O₂₇)共生结构铁电陶瓷样品.用x射线衍射对其进行微结构分析 ，并测量铁 关键词： 4Ti₃O₁₂-SrBi₄Ti₄O₁₅')" href="#">Bi₄Ti₃O₁₂-SrBi₄Ti_{4O15 La掺杂 铁电性能 居里温度 弛豫铁电}     

Photocatalytic behavior of heavy La-doped TiO2 films deposited by pulsed laser deposition using non-sintered target

We have investigated the control of photocatalytic behavior under deposited conditions of non-sintered target of different molar ratios with TiO₂ and La₂O₃ from 1:0 to 1:2 for heavily La doping, and post-annealing temperature from 600 °C to 1000 °C for crystallizing by pulsed laser deposition. We have successfully crystallized heavily La-doped TiO₂ films with post-annealing temperature over 800 °C and with molar ratio of TiO₂:La₂O₃ over 1:1 on a quartz substrate. Heavily La-doped TiO₂ films are observed the decomposition of methylene blue and a water-splitting reaction in photocatalytic behavior under Xe light irradiation. When stoichiometric La-doped TiO₂ (TiO₂:La₂O₃ = 1: 1) is synthesized with heat-treatment at 900 °C, the best results are obtained under photocatalytic behavior and pure La₂Ti₂O₇ crystalline were obtained.     

Gas-sensing properties of perovskite La0.875Ba0.125FeO3 nanocrystalline powders

La_0.875Ba_0.125FeO₃ nanocrystalline powders have been prepared by a sol-gel method. The structure, conductance and gas-sensing properties were investigated. La_0.875Ba_0.125FeO₃ crystallizes as a perovskite phase with the orthorhombic structure. The La_0.875Ba_0.125FeO₃ based sensor shows good sensitivity and selectivity to alcohol gas. The highest sensitivity to 500 ppm alcohol gas reached was 58 at 170 °C. The adsorption of O₂ on the La_0.875Ba_0.125FeO₃ (0 1 0) surface was studied with the first-principles calculation based on the density functional theory. The results show that the surface states are near the Fermi energy level and that the Fe ion plays an important role in the process of oxygen adsorption, which affects the gas-sensing properties.     

Titanium atoms dimerization phenomenon and magnetic properties of titanium-antisite (TiO) and chromium doped rutile TiO2, ab-initio calculation

The ab-initio calculations based on the Korringa Kohn Rostoker approximation approach combined with coherent potential approximation (KKR-CPA), were used to study the magnetic properties of the titanium anti-site (Ti_O) and chromium (Cr) doped TiO₂. In the considered systems, we used different concentrations for Ti_O defect and Cr doping. In TiO_2(0.98)(Ti_O)_0.02, the obtained results indicate that Ti_O is a donor having half-metal behavior. Ti_O[3d] band is located at the Fermi level, although isn’t 100% polarized, the ferromagnetic (FM) state is verified as being more stable than disordered local moment (DLM) state. For Ti_0.98Cr_0.02O₂ the Cr doping introduced new states which give the material half-metallic feature. The majority spin of Cr impurities are located at the Fermi level and the conduction electrons around the Fermi level are 100% spin polarized. This indicates the stability of (FM) state. Moreover, in Ti_0.98Cr_0.02O_2(0.98)(Ti_O)_0.02, the top of the valence band is shifted to lower energy compared to pure TiO₂, and the n-type of TiO₂ is verified. The majority spin of Cr[3d] are located at 0.025 Ry close to the Fermi level. The predicted Curie temperatures (Tc) were calculated using the mean field approximation (MFA) and we predicted that Ti_O defect in Cr doped TiO₂ makes Tc higher. This kind of defect makes the material useful for spinotronics's applications and devices.     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi₄Ti₃O₁₂和Bi_3.25La_0.75Ti₃O₁₂薄膜，研究了La掺杂对Bi₄Ti₃O₁₂薄膜的晶体结构、铁电性能和疲劳特性的影响，发现La掺杂没有改变Bi₄Ti₃O₁₂薄膜的基本晶体结构，并且提高了Bi₄Ti₃O₁₂铁电薄膜的剩余极化值和抗疲劳性能，对La掺杂改善Bi₄Ti₃O₁₂铁电薄膜性能的机理进行了讨论. 关键词： 铁电性能 4Ti₃O₁₂薄膜')" href="#">Bi₄Ti₃O₁₂薄膜 3.25La_0.75Ti₃O₁₂薄膜')" href="#">Bi_3.25La_0.75Ti₃O₁₂薄膜 sol-gel法 La掺杂     

La掺杂SrBi4Ti4O15铁电材料性能研究

按x=0.00，0.10，0.25，0.50，0.75和1.00，采用固相烧结工艺，制备了不同La掺杂量的SrBi_4-xLa_xTi₄O₁₅的陶瓷样品. 用x射线衍射对其微结构进行了分析，并测量了铁电、介电性能.结果发现，La掺杂未改变SrBi₄Ti ₄O₁₅的晶体结构.随掺杂量的增加，样品的矫顽场(E_c)下降，剩余极化(2P_{关键词： 4-x}La_xTi₄O₁₅')" href="#">SrBi_4-xLa_xTi₄O₁₅ La掺杂 铁电性能 相变温度 弛豫铁电     

Optical properties of Nb doped SrTiO3 from first principles study

The electronic and optical properties of Nb doped SrTiO₃ are studied by ab initio linear muffin-tin orbital method in the atomic sphere approximation. The equilibrium lattice constants of SrTi_1−xNb_xO₃ with x=0.0, 0.25 and 0.5 are found by minimization of the total energy curves. The computated lattice constants are in good agreement with experimental data. Our electronic band calculation shows that the Fermi level of SrTi_1−xNb_xO₃ with x≥0.125 moves into the conduction bands and the system shows metallic behavior. The numerical results indicate that the Nb impurity atoms would lead to the distortion of the band edges. The complex dielectric function of SrTiO₃ and Nb doped SrTiO₃ are calculated using the random-phase approximation. The doping effect on the optical properties of SrTi_1−xNb_xO₃ is discussed.     

La掺杂诱发层状钙钛矿型铁电体弛豫性相变的介电研究

制备了La掺杂层状钙钛矿铁电体材料SrBi₄Ti₄O₁₅, Sr₂Bi₄Ti₅O₁₈以及共生结构Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅，通过研究样品的变温介电特性发现，SrBi_4-xLa_{x 关键词： 弛豫性相变 微畴-宏畴 层状钙钛矿 介电性能}     

Study on Mn-doped SrTiO3 with first principle calculation

The defect formation energies and electronic structures of Mn doped strontium titanate have been studied using CRYSTAL-09 code. The defect formation energies for Mn_Sr and Mn_Ti, under different chemical potential conditions, have been obtained to determine the way Mn prefers to occupy in the Mn doped SrTiO₃ crystal. From the electronic structures of Mn doped SrTiO₃, it is shown that Mn_Sr cannot change the band gap of SrTiO₃. However, Mn_Ti can effectively reduce the band gap of SrTiO₃ and improve the photocatalysis.     

Investigation of half-metallic ferromagnetism in hafnium and tantalum doped NiO for spintronic applications: A DFT study

Full Potential Linearised Augmented Plane Wave (FP-LAPW) method was used to investigate the electronic and magnetic properties of NiO doped with Hf and Ta within the frame work of density functional theory (DFT). NiO is found to be stable in rock salt structure. NiO shows conducting characteristics for the lattice constant of 4.155 Å. Doping Hf and Ta in the metallic super cell of NiO separately in the doping concentration of 12.5%, the compounds Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are formed. These compounds of Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are predicted to exhibit stability in the ferromagnetic phase. The density of states and band structure plots predict that these compounds exhibit half metallic character with formation of energy gap in one of the spins at the Fermi level. The total spin magnetic moments found in these compounds are 12.00689 μ_B and 10.97628 μ_B.     

DFT study on electronic structures and optical absorption properties of C, S cation- doped SrTiO3

The effects of C cation and S cation doping on the electronic structures and optical properties of SrTiO₃ are investigated by density function theory (DFT) calculations. The calculated results reveal that the top of the valence band is predominately made up of the O 2p states for the pure SrTiO₃. When SrTiO₃ was doped with C cation and S cation, the top of the valence bands consists mainly of O 2p+C 2s hybrid orbitals and O 2p+S 3s hybrid orbitals, respectively. The band gap of SrTiO₃ is narrowed by the doping with C cation and S cation, especially for the C and S-codoped SrTiO₃. Moreover, the red shifts of the absorption edge are found by the calculated optical properties, which is consistent with reported experiment results. It is the explanation for their visible light respondency by the presence of C 2s and S 3s states on the upper edge of the valence band. All of these results can explain the good photocatalytic properties of C, S cation-codoped SrTiO₃ under visible light irradiation.      

Effect of La doping on the electronic structure and optical properties of ZnO

The electronic structure and optical properties of ZnO doped with La have been investigated using density functional theory based on first-principles ultrasoft pseudopotential method. The calculated results show that the La doping increases the bandgap of ZnO, in agreement with the experimental results; while the Fermi level shifts into the conduction band, revealing the so-called Burstein-Moss effect. In comparison to pure ZnO, a new peak appears in the imaginary part of dielectric function in the system doped with La and the optical absorption edge has been obviously changed. Moreover, the covalent property of Zn_1−xLa_xO is found to weaken with the increase of La concentration.     

First-principle study of electronic structure and stability of Sn0.5Sb0.5O2

A theoretical study on Sb-doped SnO₂ has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA) level. Stability and conductivity analyses were performed based on the formation energy and electronic structures. The results show that Sn_0.5Sb_0.5O₂ solid solution is stable because the formation energy of Sn_0.5Sb_0.5O₂ is −0.06 eV. The calculated energy band structure and density of states showed that the band gap of SnO₂ narrowed due to the presence of the Sb impurity energy levels in the bottom of the conduction band, namely there is Sb 5s distribution of electronic states from the Fermi level to the bottom of conduction band after the doping of antimony. The studies provide a theoretical basis to the development and application of Sn_1−xSb_xO₂ solid solution electrode.     

过渡金属(Fe,Co,Ni,Zn)掺杂金红石TiO2的电子结构和光学性质

采用基于密度泛函理论的第一性原理方法对未掺杂以及不同浓度过渡金属Fe,Co,Ni,Zn掺杂金红石TiO₂的超晶胞体系进行了几何优化,并讨论了其晶格常数,电子能带结构和光学性质.研究结果表明:掺杂前后的晶格参数与实验值偏差在3.6%以下;适量的过渡金属掺杂不但影响体系能带结构,拓宽光吸收范围,而且扮演着俘获电子的重要角色,有利于光生电子-空穴对的有效分离以及增强光吸收能力;Fe,Co,Ni,Zn最佳理论掺杂体系分别为Ti_0.75Fe_0.25O₂,Ti_0.75Co_0.25O₂,Ti_0.75Ni_0.25O₂,Ti_0.83Zn_0.17O₂;Fe,Co,Ni3d态分裂为t_2g和e_g态,分别贡献于价带高能级和导带低能级部分,促进了电子-空穴对的生成,从而可提高TiO₂的光催化性能;Zn3d态电子成对填满轨道,不易被激发,故光催化活性无明显提高.