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.     

First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3

The effects of La and Sb doping on the electronic structure and optical properties of SrTiO 3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO 6 octahedra dominate the main electronic properties of SrTiO 3 , and its structural stability can be improved by La doping. The La 3+ ion fully acts as an electron donor in Sr 0.875 La 0.125 TiO 3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb 0.125 Ti 0.875 O 3 , there is a distortion near the bottom of the CBs for SrSb 0.125 Ti 0.875 O 3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr0.875La0.125TiO3 and SrSb0.125Ti0.875O3 , respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95% in most of the visible region, which is higher than that of Sr0.875La0.125TiO3 (85%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb0.125 Ti0.875 O3 .     

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.     

Transport Behaviour of La0.8Sr0.2AlO3 Thin Film on Oxygen Deficient SrTiO3 Substrate

La_0.8Sr_0.2AlO₃ (LSAO) thin films are grown on SrTiO₃ (STO) and MgO substrates by laser molecular beam epitaxy. The LSAO thin film on oxygen deficient STO substrate exhibits metallic behaviour over the temperature range of 80--340K. The optical transmittance spectrum indicates that theLSAO thin films on MgO substrate are insulating at room temperature. The transport properties of LSAO thin films on STO substrates deposited in different oxygen pressure are compared. Our results indicate that oxygen vacancies in STO substrates should be mainly responsible for the transport behaviour of LSAO thin films.     

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.     

Adsorption and Reaction of CO on （100） Surface of SrTiO3 by Density Function Theory Calculation

Adsorption and reaction of CO on two possible terminations of SrTiO3 （100） surface are investigated by the first-principles calculation of plane wave ultrasoft pseudopotentiai based on the density function theory. The adsorption energy, Mulliken population analysis, density of states （DOS） and electronic density difference of CO on SrTiO3 （100） surface, which have never been investigated before as far as we know are performed. The calculated results reveal that the Ti-CO orientation is the most stable configuration and the adsorption energy （0.449eV） is quite small. CO molecules adsorb weakly on the SrTiO3 （100） surface, there is predominantly electrostatic attraction between CO and the surface rather than a chemical bonding mechanism.     

VUV/UV/X-Ray Excited Luminescent Properties of Eu^3＋ and Pr^3＋ Doped BiSbO4

Absorption spectra of BiSbO4 are studied. The electronic structure calculated by the DFT shows that BiSbO4 is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu^3＋ and Pr^3＋ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu^3＋ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu^3＋ ions occupied Bi^3＋ sites, and there could be an energy transfer from Bi^3＋ ions to RE^3＋ ions.     

Acceptor Concentration Effects on Photovoltaic Response in the La1-xSrxMnO3/SrNbyTi1-yO3 Heterojunction

Photovoltaic response in the heterojunction of La1-x SrxMnO3/SrNby Ti1-yO3 （LSMO/SNTO） is analyzed theoretically based on the drift-diffusion model. It is found that the decrease of acceptor concentration in the La1-xSrxMnO3 layer of hereto junction can increase the peak value of photovoltaic signal and the speed of photovoltaic response, whereas the changing of donor concentration in the SrNby Ti1-yO3 layer has no such evident effect. Furthermore, the result also indicates that the modulation of Sr doping in La1-xSrxMnO3 is an effective method to accommodate the sensitivity and the speed of photovoltaic response for LSMO/SNTO photoelectric devices.     

Structural and electrical properties of La0.5Sr0.5CoO3 films on SrTiO3 and porous a-Al2O3 substrates

Films of La_0.5Sr_0.5CoO₃ (LSCO) have been deposited on specially treated TiO₂-terminated (001) SrTiO₃ substrate surfaces and on macroporous polycrystalline !-Al₂O₃ substrates, having a mean pore diameter of 80 nm, by pulsed laser deposition. The films deposited on SrTiO₃ are good conducting, (001) textured, and exceptionally smooth (1-2 Å for 100 nm thick films). LSCO films deposited on porous !-Al₂O₃ are polycrystalline and exhibit good crystallographic and electrical properties despite the large substrate roughness and the differences in lattice parameters and crystal structure between the film and the substrate. Different growth modes have been observed on the porous !-Al₂O₃ substrates depending on the oxygen pressure during film deposition. Films grown at an oxygen pressure of 10^-1 mbar are macroporous, whereas films grown at 10^-2 mbar completely cover the substrate pores. In the latter case, strain effects lead to film cracking.     

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes

New methods for fabricating highly 𘚡¢-oriented and complete 𘜏¢-textured Pb(Ta_0.05Zr_0.48Ti_0.47)O₃ (PTZT) films on Pt/TiO₂/SiO₂/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La_0.25Sr_0.75CoO₃ and SrRuO₃ electrodes. The 𘚡¢-preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1᎒¹⁰ switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the 𘜏¢-textured PTZT film capacitor retains 94.7% of its polarization after 1.5᎒¹⁰ switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.     

Electronic structure and optical properties of In-doped SrTiO3 by density function theory

The effect of In doping on the electronic structure and optical properties of SrTiO3 is investigated by the first-principles calculation of plane wave ultra-soft pseudo-potential based on the density function theory （DFT）. The calculated results reveal that due to the hole doping, the Fermi level shifts into valence bands （VBs） for SrTi1-x InxO3 with x = 0.125 and the system exhibits p-type degenerate semiconductor features. It is suggested according to the density of states （DOS） of SrTi0.875In0.125O3 that the band structure of p-type SrTIO3 can be described by a rigid band model. At the same time, the DOS shifts towards high energies and the optical band gap is broadened. 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 film. The optical transmittance of In doped SrTiO3 is higher than 85% in a visible region, and the transmittance improves greatly. And the cut-off wavelength shifts into a blue-light region with the increase of In doping concentration.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Novel Na3Y9O3（BO3）8：Tb^3＋ Phosphor

The novel vacuum ultraviolet （VUV） excited Na3 Y9O3 （BO3）8：Tb^3＋ （NYOB：Tb^3＋） green phosphor is prepared. Strong VUV photoluminescence and high quenching concentration of Tb^3＋ （20 wt%） are observed in NYOB： Tb^3＋ and the strong emission are correlated with the unique layer-type structure of NYOB. All the characteristic 4 f - 5d transitions of Tb^3＋ and the host absorption band in VUV region are identified in the excitation spectrum. Based on the results, the energy levels scheme of Tb^3＋ in NYOB：Tb^3＋ is first established. This newly developed NYOB：Tb^3＋ phosphor shows excellent optical properties when compared with the commercial Zn2SiO4：Mn^2＋ and would be a potential VUV-excited green phosphor.     

Ga掺杂对纤锌矿TM_(0.125)Zn_(0.875)O(TM=Be,Mg)电子结构和光学能隙的影响

利用密度泛函理论的平面波超软赝势方法,对纤锌矿T M_(0.125)Zn_(0.875)O(TM=Be,Mg)合金和Ga掺杂T M_(0.125)Zn_(0.875)O的结构参数、能带、电子态密度和光学能隙进行计算和分析,结果表明:T M_(0.125)Zn_(0.875)O掺入Ga容易实现并且结构更稳定,T M_(0.125)Zn_(0.875)O合金掺Ga能获得很好的n型材料改性,能隙由导带底Ga 4s态和价带顶O 2p态决定,由于Bllrstein-Moss移动和多体效应,Ga掺杂后的T M_(0.125)Zn_(0.875)O光学能隙变大,这与实验结果相一致,T M_(0.125)Zn_(0.875)O掺Ga材料可作透明导电薄膜应用到紫外和深紫外光电子器件中。     

Theoretical Study of Interesting Fine-Structure Splittings for 23P0, 1, 2 States along Helium Isoelectronic Sequence

Using the multi-configuration Dirac Fock method including the Breit interactions and QED corrections, we calculate the fine-structure energy levels of the 2^3 Po, 1,2 states along the helium isoelectronic sequence with atomic number up to Z = 36, where LS-coupling is appropriate. Our calculation results agree with the experimental results within about 1%. We elucidate the mechanism of the interesting fine-structure splittings for the 2^3Po,1,2 states along the helium isoelectronic sequence, i.e. the competitions between the spin-orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions.     

Cs^＋-K^＋ Exchange in Z-Cut KTiOPO4 Crystal Covered with Chromium Masking Layer

Cs^＋-K^＋ ion exchanges are performed on z-cut KTiOPO4 crystals with chromium coating covered. The temperature of ion exchange is 430℃, and the time range from 15min to 30min. The dark mode spectra of the samples are measured by the prism coupling method. The channel structures on the samples are observed by a microscope and the near field pattern of the channel waveguides are measured by the end-fire coupling method. The refractive index of the samples increases and the increments at surface are modulated due to the existence of Cr film. In the region covered by Cr film, the refractive index of the samples at the surface increases dramatically in a shallow layer. The results of energy dispersive x-ray spectra indicate that in the region covered with Cr film, Cr ions participate in the ion exchange process, and enhance the refractive index. The results may provide a possibility that achieves index enhancement and Cr doping synchronically.     

First-principles calculations on TiO2 doped by N, Nd, and vacancy

First-principles density functional theory calculations have been carried out to investigate electronic structures of anatase TiO₂ with substitutional dopants of N, Nd, and vacancy, which replace O, Ti, and O, respectively. The calculation on N-doped TiO₂ with the local density approximation (LDA) demonstrates that N doping introduces some states located at the valence band maximum and thus makes the original band gap of TiO₂ smaller. Examining the effect of the strong correlation of Nd 4f electrons on the electronic structure of Nd-doped TiO₂, we have obtained the half-metallic ground state with the LDA and the insulating ground state with the LDA+U (Hubbard coefficient), respectively. In addition, the calculation on vacancy-doped TiO₂ with the LDA shows that a vacancy can induce some states in the band-gap region, which act as shallow donors.     

La2CuO4+δ和La2-xSrxCuO4系统中的电子输运性质

 本文解释了La₂CuO_4+δ（0≤δ≤0.09）和La_2-xSr_xCuO₄（0≤x≤0.3）两种p型系统含铜稀土氧化物中的电阻和Seebeck系数与温度的依赖关系，在室温以上，一氧大气压下的La₂CuO_4+δ系统趋于失氧；在500 K以上，超导样品显示出失氧的一级相变，并且恢复到反铁磁相。在转变温度T₁≈300 K以下，对0<δ<0.05成份的样品，相分离成反铁磁相和超导相；而在T_cρ≈100 K的温度范围内，超导相进一步分离成富空穴和贫空穴畴。在0.04≤δ≤0.09范围内，T_c处的电阻陡降出现了台阶；我们认为，它反映了电子成对的起伏。在La_2-xSr_xCuO₄系统中，对于成分为01≈300 K以上，空穴的运动是弥散的，但是ΔH_m=0；而对于x≥0.22的样品，经历了从平滑到Fermi液态的转变。成份为0c1范围（其中空穴继续以弥散方式运动）是亚稳的，但是，在T_cρ≤150 K范围，出现了电荷起伏。当样品冷却通过T₁时，对于成份为0.15≤x≤0.2的样品，经历了由弥散到强质量增强巡游电子状态的转变；在T_c处，从均匀的修饰电子的正常态凝聚成超导的载流子对。在超导成份样品的正常态中，不寻常的电子-晶格相互作用，可以归结为在CuO₂面上从更离子性的到共价性的Cu:3d_x²-r²─O:P_σ键合的转变；通过这种转变，轨道杂化和Hubbard U参量随Cu─O键长和Cu原子上的外表局域氧化态都产生灵敏的变化。     

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.     

Effect of TiO2 Nanotubes on Polymer-Fullerene Bulk Heterojunction Solar Cells

We investigate the photovoltaic properties of hybrid organ/c solar cell based on the blend of poly[2-methoxy-5-（2- ethylhexoxy-l,4-phenylenevinylene） （MEH-PPV）, C60 and titanium dioxide （TiO2） nanotubes. In comparison of the composite devices with different TiO2：[MEH-PPV ＋C60] weight ratios of lw$.% （D1-1）, 2wt.% （D1-2）, 3wt.% （D1-3）, 5wt.% （D1-4）, 10wt.% （D1-5） and 20wt.% （D1-6）, it is found that the device Dl-a exhibits the best performance. The conversion efficiency is improved by a factor of 3 compared with the MEH-PPV：C60 device.     

Correlation between Light Emissions from Amorphous-Si：H/SiO2 and nc-Si/SiO2 Multilayers

We investigate the properties of light emission from amorphous-Si：H/SiO2 and nc-Si/SiO2 multilayers （MLs）. The size dependence of light emission is well exhibited when the a-Si：H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.