Density functional theory analysis of electronic structure and optical properties of La-doped Cd_2SnO_4 transparent conducting oxide

The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd_2SnO_4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U method, we show that Cd_2SnO_4 is a direct band-gap semiconductor with a band gap of 2.216 eV, the band gap decreases to 2.02 e V and the Fermi energy level moves to the conduction band after La doping. The density of states of Cd_2SnO_4 shows that the bottom of the conduction band is composed of Cd 5 s, Sn 5 s, and Sn 5 p orbits, the top of the valence band is composed of Cd 4d and O 2p, and the La 5 d orbital is hybridized with the O 2 p orbital, which plays a key role at the conduction band bottom after La doping. The effective masses at the conduction band bottom of pure and La-doped Cd_2SnO_4 are 0.18 m0 and 0.092 m_0, respectively, which indicates that the electrical conductivity of Cd_2SnO_4 after La doping is improved. The calculated optical properties show that the optical transmittance of La-doped Cd_2SnO_4 is 92%, the optical absorption edge is slightly blue shifted, and the optical band gap is increased to 3.263 eV. All the results indicate that the conductivity and optical transmittance of Cd_2SnO_4 can be improved by doping La.     

Textured superconducting phase in the heavy fermion CeRhIn5

When antiferromagnetism and unconventional superconductivity coexist in CeRhIn(5) there is a significant temperature difference between resistively and thermodynamically determined transitions into the superconducting state. In this state, anisotropic transport near the superconducting transition reveals the emergence of textured superconducting planes that appear without a change in translational symmetry of the lattice. CeRhIn(5) is not unique in exhibiting these behaviors, indicating that textured superconductivity may be a general consequence of coexisting orders in correlated electron materials.     

Electronic structure of CeRhX (X = Sn,In)

Electronic structure of the compounds CeRhIn and CeRhSn have been studied by the X-ray photoemission spectroscopy (XPS) and ab initio band structure calculations. CeRhSn shows the non-Fermi liquid characteristics at low temperatures, while CeRhIn exhibits a Fermi-liquid ground state. At ambient temperature the XPS data reveal an intermediate valence state of Ce ions in both systems. The Ce core-level XPS spectra are very similar and indicate the strong coupling of the Ce 4f and the conduction band states (Δ ≈ 100 meV). The valence band spectra we interpret with the help of ab initio calculations as well as using the results for the reference compounds LaRhIn and LaRhSn. The comparative analysis of the theoretical band structures and charge density plots reveal the changes in chemical bonding and the hybridization between the Ce 4f and the other valence states introduced by the replacement of In by Sn atoms. The more covalent character of the chemical bonding in the stannides is in line with the smaller thermal expansion. Finally, for CeRhIn we found a typical temperature dependence of the crystal lattice, while CeRhSn shows distinct anomaly at about 120 K, presumably related to the change in planar Ce–Rh bonds.     

The effect of doping by IV-family elements on the electronic structure and electrical characteristics of Sb2O5

The electronic structures of doped Sb₂O₅ by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results showed that the substituted IV-family elements act as acceptors in Sb₂O₅. Partial DOSs indicates that by substituting Ge(Ge _Sb ) or Sn(Sn _Sb ), there may be a larger contribution to the total DOSs near E _F than by substituting Si, which suggests that doping Ge or Sn in Sb₂O₅ produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely to exist in the substituted position rather than in the interstitial position in Sb₂O₅, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb₂O₅. Ionization energy results show that Ge _Sb or SnSb, two among the three impurities considered, act as shallow acceptors in Sb₂O₅, thus producing a higher concentration of holes.      

纳米Au/CeO2催化剂的La2O3改性及光谱表征

采用沉积沉淀法合成了系列La2O3改性的Au/CeO2催化剂,并结合紫外可见漫反射光谱,X射线粉末衍射和透射电镜对其进行相关表征。La的引入改变了载体的结构缺陷,导致了体系中金属Au与载体的相互作用发生了不同程度的变化。La2O3的掺杂有利于提高载体CeO2中氧缺位浓度,在一定范围内有利于活性的提高。继续提高掺杂量,使得缺陷浓度过高时可能形成缺陷簇,改变了缺陷性质,反而使活性相对下降。La掺杂量为5at%的Au/CL5.0样品表现出最佳的WGS活性,300℃时CO转化率达到94.12%。     

Pressure-induced superconductivity in quasi-2D CeRhIn5

CeRhIn5 is a new heavy-electron material that crystallizes in a quasi-2D structure that can be viewed as alternating layers of CeIn3 and RhIn2 stacked sequentially along the tetragonal c axis. Application of hydrostatic pressure induces a first-order-like transition from an unconventional antiferromagnetic state to a superconducting state with T(c) = 2.1 K.     

Effect of Sn doping on the martensitic and premartensitic transitions in Ni2MnGa

The effect of Sn doping at the Ga site of Ni₂MnGa is investigated through magnetic and magneto-transport measurements. Clear signatures of martensitic and premartensitic transitions are observed in the pure as well as in 5% Sn doped alloy. For 10% Sn doping, the martensitic transition vanishes, while the premartensitic transition remains visible at low temperature. All the samples are found to have a ferromagnetic ground state with saturation moment decreasing with increasing Sn concentration. The magnetocaloric effect near the martensitic transition in the pure and 5% Sn doped samples is found to be positive. However, the entropy change is found to decrease with increasing magnetic field, which is particularly prominent in the undoped sample. The samples also show negative magnetoresistance with anomalies at the martensitic and premartensitic transition points.     

The influence of oxygen deficiency and Sb doping on inverse photoemission spectra of SnO2

The changes in the empty electronic states in SnO₂ produced by ion-beam induced oxygen deficiency and by Sb doping have been studied by inverse photoemission spectroscopy. Inverse photoemission in SnO₂ itself is dominated by peaks 4 and 12 eV above the Fermi level, the former associated with empty states of dominant Sn 5p atomic character. Sb doping populates states in the Sn 5s conduction band, shifting the empty state structure closer to the Fermi energy. By contrast oxygen deficiency introduces new states above the main Sn 5p peak. These are tentatively described as 5s-5p hybrids pushed up in energy from the 5p band by mixing between atomic orbitais of different parity in the non-centrosymmetric cation environment of oxygen deficient SnO₂.     

Influence of Ag and Sn incorporation in In_2S_3 thin films

Ag- and Sn-doped In2S3 thin films were deposited on glass substrates using the thermal evaporation technique. The doping was realized by thermal diffusion. The influences of Ag and Sn impurities on the electrical, structural, morphological, and optical properties of the In2S3 films were investigated. In all deposited samples, the x-ray diffraction spectra revealed the formation of cubic In2S3 phase. A significant increase in the crystallite size was observed after Ag doping,while the doping of Sn slightly decreased the crystallite size. The x-ray photoelectron spectroscopy verified the diffusion of Ag and Sn into the In2S3 films after annealing. The optical study illustrated that Ag doping resulted in a reduction of the optical band gap while Sn doping led to a widening of the gap. Optical properties were investigated to determine the optical constants. Besides, it was found that the resistivity decreases significantly either after Ag or Sn incorporation. The study demonstrates that the Sn-doped In2S3 thin films are more suitable for buffer layer application in solar cells than the Ag-doped In2S3 thin films.     

超导体Bi1.8Pb0.2Sr2-xLaxCuOy的电阻率和热电势研究

本文对名义组份为Bi1.8Pb0.2Sr2-xLaxCuOy系列样品的电阻率和热电势特性进行了实验研究.测量表明,Pb掺杂可以进一步提高超导转变温度Tc ;随着La含量的增加,Tc 按照典型的抛物线型规律变化;La掺杂极大地影响超导体正常态的输运特性.我们的分析指出,热电势在正常态所表现出的规律与高温超导机制密切相关,而且电阻率正常态输运特性的变化可用La掺杂造成CuO6八面体顶点氧发生位移来解释.     

La掺杂和空位对ZnS磁性和光学性能影响的第一性原理研究

利用密度泛函理论框架下的平面波超软赝势法,通过第一性原理对La掺杂与Zn空位(V_(Zn))及La掺杂与S空位(V_S)共存的ZnS体系的电子结构、磁性机理、形成能及吸收光谱进行了研究.结果表明, La掺杂与空位(V_(Zn)或V_S)的空间位置最近时,掺杂体系的形成能最低,体系最稳定.另外,La掺杂与Zn空位共存时,体系具有磁性,且体系的净磁矩与La原子与Zn空位的相对位置有关;La掺杂与S空位共存时,掺杂体系无磁性,但此时体系的禁带宽度最窄且吸收光谱红移最显著.     

Dielectric, magnetic and magnetoelectric properties of La and Nb codoped bismuth ferrite

Single-phase Bi(0.80)La(0.20)FeO(3) (BLFO) and Bi(0.80)La(0.20)Fe(1-x)Nb(x)O(3) (BLFNO) samples were prepared in order to study the dielectric, magnetic and magnetoelectric properties of La and Nb codoped BiFeO3. Rietveld refinement of x-ray diffraction patterns of La and Nb codoped samples has been performed using the R3c space group. Magnetic hysteresis loops revealed that codoping can effectively increase the spontaneous magnetization due to change in the bond angle of Fe-O-Fe as a result of distortion created by the Nb5+ doping. Magnetic field-induced relative change of the dielectric constant for BLFO and BLFNO samples is a signature of magnetoelectric coupling.     

Co,Sn共掺ZnO薄膜结构与光致发光的研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co,Sn掺杂ZnO系列薄膜.通过金相显微镜和X射线衍射(XRD)研究了Co与Sn掺杂对薄膜的表面形貌和微结构的影响.XRD结果表明,所有ZnO薄膜样品都存在(002)择优取向,特别Sn单掺ZnO薄膜的c轴择优取向最为显著,而且晶粒尺寸最大.XPS测试表明样品中Co和Sn的价态分别为2+和4+,证实Co²⁺,Sn⁴⁺进入了ZnO的晶格.室温光致发光谱(PL)显示在所有的样品中都有较强的蓝光双峰发射和较弱的绿光发 关键词： ZnO薄膜 溶胶-凝胶 掺杂 光致发光     

La_(0.7-x)Gd_xSr_(0.3)MnO_3(x=0.20,0.30,0.40,0.50)的TCR研究(英文)

研究了La位Gd掺杂对La0.7-xGdxSr0.3MnO3(x=0.20,0.30,0.40,0.50)体系的电阻温度系数(TCR)的影响.实验结果表明:Gd掺杂将引起电阻率曲线的急剧变化,导致出现大的TCR;而且随Gd掺杂的增加,TCR在x=0.30出现峰值,然后随掺杂量增加逐步降低.体系出现大的TCR,来源于Gd掺杂引起的额外磁性耦合.     

Valence transition and magnetic ordering in Sn doped EuPd2Si2

The sharp, temperature induced, continuous valence transition in EuPd₂Si₂ is drastically changed by doping with Sn at the Si site upto 5 at. %. Only a first order valence transition occurs for a 3% Sn doped sample and the 2⁺ component which survives the valence transition orders magnetically at 4.2 K. No valence transition at all occurs for a 5% Sn doped sample right up to 1.9 K and magnetic ordering sets in around 30 K.     

Perturbation of Ge(1 1 1) and Si(1 1 1)√3α-Sn surfaces by adsorption of dopants

We test the response of the √3 × √3α reconstructions formed by 1/3 monolayer of tin adatoms on silicon and germanium (1 1 1) surfaces upon doping with electrons or holes, using potassium or iodine as probes/perturbers of the initial electronic structures. From detailed synchrotron radiation photoelectron spectroscopy studies we show that doping with either electrons or holes plays a complimentary role on the Si and Ge surfaces and, especially, leads to complete conversion of the Sn 4d two-component spectra into single line shapes. We find that the low binding energy component of the Sn core level for both Si and Ge surfaces corresponds to Sn adatoms with higher electronic charge, than the Sn adatoms that contribute to the core level high binding energy signal. This could be analyzed as Sn adatoms with different valence state.     

Strain glass behaviour of Ni–Co–Mn–Sn ferromagnetic shape memory alloys

We report the direct experimental observations of the glassy behaviour in Ni–Co–Mn–Sn ferromagnetic shape memory alloys by doping sufficient substitutional point defect Co into the Ni sites (9 at%). The results showed that high level of Co doping had caused the complete suppression of the martensitic transformation and introduction of a strain glass transition in Ni–Co–Mn–Sn alloys. The strain glass transition was definitively characterized by the dynamic mechanical anomalies following the Vogel–Fulcher relationship and the signature nonergodicity of the frozen glass using a zero‐field‐cooled/field‐cooled heating measurement of static strain. The findings clarified the cause of vanishing of the martensitic transformation in Ni–Co–Mn–Sn alloy with high Co doping levels and the generality of glassy state in Ni–Mn based ferromagnetic shape memory alloys with high level of foreign elements doping. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

La-Ce-TiO_2纳米光催化剂的溶胶-微波法合成、谱学表征及其活性研究

以钛酸四丁酯为原料,采用溶胶-微波法(Sol-Microwave Method)合成了镧和铈共掺型纳米TiO2粉体(La-Ce-TiO2),借助XRD、XPS和UV-Vis等测试手段对其进行了表征,并以甲基橙为模型污染物考察了掺杂量对样品光催化活性的影响规律.XRD分析表明,所得粉体均为锐钛矿相纳米TiO2,且稀土元素镧和铈掺杂后纳米TiO2特征衍射峰宽化,强度降低;XPS分析表明,镧和铈掺杂后样品表面存在大量的氧缺位;UV-Vis吸收光谱表明,所得粉体在400 nm以下均有连续宽化的吸收带,且La和Ce掺杂后样品对光的吸收显著增强,这足由于La(Ⅲ)-O荷移跃迁以及Ce(Ⅳ)f→d跃迁和Ce(Ⅳ)-O荷移跃迁所致;光催化实验表明,La和Ce共掺杂能显著提高纳米TiO2的光催化活性,其中当La(Ⅲ)和Ce(Ⅳ)掺杂量分别为2%和0.04%时,纳米TiO2光催化剂具有较高的催化活性,自然光照射下光催化氧化处理卷烟厂蒸叶车间废水,效果较好,废水COD去除率达到86.11%.     

Property enhancement of transparent conducting zinc oxide thin films—Effect of simultaneous (Sn+F) doping

Undoped and simultaneously (Sn+F) doped ZnO thin films were fabricated using a simplified spray pyrolysis technique and the effects of Sn doping level on their electrical, structural, optical and surface morphological properties were studied. The XRD patterns confirmed the hexagonal wurtzite structure of ZnO. The minimum electrical resistivity of 0.45×10⁻² Ω cm was obtained for ZnO films having Sn+F doping levels of 8+20 at%. All the films exhibited average optical transmittance of 85% in the visible region, suitable for transparent electrode applications. The overall quality of the fabricated films was confirmed from photoluminescence (PL) studies. The PL and surface morphological studies along with the elemental analysis showed the increase of Sn diffusion into the ZnO lattice which was consistent with the concentration of Sn in the starting solution. The results of the analysis of physical properties of simultaneously doped ZnO films proved that these films might be considered as promising candidates for solar cells and other opto-electronic applications.     

Effect of doping concentration on the structural and optical properties of pure and tin doped zinc oxide thin films by nebulizer spray pyrolysis (NSP) technique

Pure and tin doped zinc oxide (Sn:ZnO) thin films were prepared for the first time by NSP technique using aqueous solutions of zinc acetate dehydrate, tin (IV) chloride fendahydrate and methanol. X-ray diffraction patterns confirm that the films are polycrystalline in nature exhibiting hexagonal wurtzite type, with (0 0 2) as preferred orientation. The structural parameters such as lattice constant (‘a’ and ‘c’), crystallite size, dislocation density, micro strain, stress and texture coefficient were calculated from X-ray diffraction studies. Surface morphology was found to be modified with increasing Sn doping concentration. The ZnO films have high transmittance 85% in the visible region, and the transmittance is found to be decreased with the increase of Sn doping concentration. The corresponding optical band gap decreases from 3.25 to 3.08 eV. Room temperature photoluminescence reveals the sharp emission of strong UV peak at 400 nm (3.10 eV) and a strong sharp green luminescence at 528 nm (2.34 eV) in the Sn doped ZnO films. The electrical resistivity is found to be 10⁶ Ω-cm at higher temperature and 10⁵ Ω-cm at lower temperature.