含空位和杂质缺陷的LiFePO4电子结构的第一性原理计算

采用基于密度泛函理论的第一性原理研究了含空位和杂质缺陷的LiFePO_4电子结构,通过能带、态密度、布居分布分析,阐明缺陷及阴离子掺杂对材料电化学性能的影响,为LiFePO_4的结构设计和实验研究提供理论基础。结果表明,Li、Fe和O空位型缺陷对LiFePO_4的带型变化影响较小,禁带中无新的导带,禁带宽度有一定程度缩小,有利于电子的传导,但总能量上升,造成结构的不稳定性,在实际高温制备过程中,可能产生少量杂相,影响LiFePO_4正极材料的电化学性能;P空位缺陷对LiFePO_4的带型影响同样较小,但在禁带中产生了两条新的导带,禁带宽度明显变窄,有利于电子的传导,虽然总能量上升,造成结构的不稳定性,但在实际高温制备过程中,可能产生微量有利于电化学性能的杂相;F掺杂LiFePO_4的带型出现了明显的变化,半导体类型由p型转变为n型,极大地促进了电子的导电性,总能量下降,结构稳定,对LiFePO_4正极材料的电化学性能有正面的影响。     

p型透明导电氧化物CuCr1-x Cax O2的制备与光电性质研究

Transparant conducting oxides showing the combination of high electrical conductivity and high transparency for visible light have been based on electron doping into a conduction band. For p-type delafossite oxides,the valence band is commonly the oxygen 2p band. Doping to produce holes in this band but the electronic conductivity of such p-type oxides is highly activated and can generally only be measured at temperatures well above room temperature. So it is very desirable to improve conductivity by doping wide-gap delafossites as transparant conducting oxides nowadays. The article reported the prepration and characterization of Ca-doped CuCrO2 monophasic delafossites. It was found that conductivity had a notable improvement after Ca-doped and reached 3. 2×10-2 S/cm for x=0.06 Ca-doped at room temperature and the structures had not been changed. The temperature dependence of electrical conductivity around room temperture was consistent with thermal activation type very well from 200 K to 300 K. The activation energe was 0. 36 eV before doping,but it changed to 0.27 eV when Ca-doped. This phenomenon suggest that in pure non-doped CuCrO2,carrier was the Cu+ d. After Ca-doped,the Cu2+ was formed from the Cu+ by a charge compensating process when the divalent Ca2+ substituted for the trivalent Cr3+ . The Seebeck coefficients being large positive constants implied that all the samples were p-type conducting oxides.     

Electronic structure and band gaps in cationic heterocyclic oligomers. Multidimensional analysis of the interplay of heteroatoms, substituents, molecular length, and charge on redox and transparency characteristics

Oxidative doping of extended pi-conjugated polymers and oligomers produces dramatic changes in optical and electrical properties, arising from polaron and soliton-derived midgap states. Despite the great importance of such changes for materials properties, far less is known about the cationic polaron states than about the neutral, semiconducting or insulating, undoped materials. The systematic, multifactor computational analysis of oligoheterocycles such as oligothiophenes, oligofurans, and oligopyrroles presented here affords qualitative and quantitative understanding of the interplay among skeletal substitution pattern, electronic structure, and the effective band gap reduction on p-doping. A simple linear relation is derived for predicting p-doped oligomer and polymer effective band gaps based on those of the neutral oligomers; this relationship confirms the effectiveness of a "fixed band" approximation and explains the counterintuitive increase of the effective band gap on p-doping of many small band gap oligomers. The present analysis also suggests new candidates for transparent conductive polymers and predicts limiting behavior of ionization potential, electron affinity, and other properties for various polyheterocyclic systems. The results yield insight into materials constraints in electrochromic polymers as well as on p- and n-type conductors and semiconductors.     

Donor-mediated band gap reduction in a homologous series of conjugated polymers

A family of six donor-acceptor-donor monomers was synthesized using combinations of thiophene, 3,4-ethylenedioxythiophene and 3,4-ethylenedioxypyrrole as donor moieties, and cyanovinylene as the acceptor moiety, to understand the effects of modified donor ability on the optoelectronic and redox properties of the resulting electropolymerized materials. Spectroelectrochemistry, differential pulse voltammetry, and cyclic voltammetry results indicate band gaps ranging from 1.1 to 1.6 eV and suggest that these polymers can be both p-type and n-type doped at accessible potentials. In situ conductivity results indicate that the n-type conductivity magnitude is modest, and the conductivity profile indicates a redox conductivity mechanism as opposed to a delocalized electronic band mechanism as observed for p-type doping.     

Basic materials physics of transparent conducting oxides

Materials displaying the remarkable combination of high electrical conductivity and optical transparency already from the basis of many important technological applications, including flat panel displays, solar energy capture and other opto-electronic devices. Here we present the basic materials physics of these important materials centred on the nature of the doping process to generate n-type conductivity in transparent conducting oxides, the associated transition to the metallic (conducting) state and the detailed properties of the degenerate itinerant electron gas. The aim is to fully understand the origins of the basic performance limits of known materials and to set the scene for new or improved materials which will breach those limits for new-generation transparent conducting materials, either oxides, or beyond oxides.     

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 ? cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.     

Achievement of highly conductive p-type transparent NdCuOS film with Cu deficiency and effective doping

Future advanced invisible or transparent electronics necessitate the need to overcome the well-known challenge in achieving high-performance p-type transparent semiconducting oxides (TSOs). Here, we report our success in achieving an outstanding p-type TSO thin film NdCuOS, which is the best performing p-type TSO reported to date based on the figure of merit (FoM) according to the best of our knowledge. In this work, we designed a novel chemical solution method to prepare the highly performing NdCuOS films with different doping elements. Our success in using a chemical solution method to grow semiconducting NdCuOS demonstrates that highly conductive oxychalcogenide films are possible to be prepared by a solution method. Such a solution method is facile, economically efficient, and scalable. Among our NdCuOS films with different dopants, we find that Mg-doped NdCuOS film demonstrates a very high p-type conductivity of 52.1 S cm^?1 and optical transmittance of 54.3% with a huge FoM value of 1706 μS. This surpassed all the other p-type films reported so far in terms of FoM. Strong photoluminescence peaks at 3.0 eV are observed for our films, indicating their great potential applications for UV or blue light LED and other devices. The science behind such a successful achievement of high-performance p-type NdCuOS film is analyzed and discussed. A transparent p-n diode with very low leakage current (9.12  μA at ?3 V) and turn-on voltage (1.1 V) is successfully fabricated, and it demonstrates a good device performance.     

Thermoelectrics with earth abundant elements: high performance p-type PbS nanostructured with SrS and CaS

We report high thermoelectric performance in nanostructured p-type PbS, a material consisting of highly earth abundant and inexpensive elements. The high level of Na doping switched intrinsic n-type PbS to p-type and substantially raised the power factor maximum for pure PbS to ~9.0 μW cm(-1) K(-2) at >723 K using 2.5 at. % Na as the hole dopant. Contrary to that of PbTe, no enhancement in the Hall coefficient occurs at high temperature for heavily doped p-type PbS, indicating a single band model and no heavy hole band. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding SrS or CaS, which form a combination of a nanostructured/solid solution material as determined by transmission electron microscopy. We find that both nanoscale precipitates and point defects play an important role in reducing the lattice thermal conductivity, but the contribution from nanoscale precipitates of SrS is greater than that of CaS, whereas the contribution from point defects in the case of CaS is greater than that of SrS. Theoretical calculations of the lattice thermal conductivity based on the modified Callaway model reveal that both nanostructures and point defects (solid solution) effectively scatter phonons in this system. The lattice thermal conductivity at 723 K can be reduced by ~50% by introducing up to 4.0 at. % of either SrS or CaS. As a consequence, ZT values as high as 1.22 and 1.12 at 923 K can be achieved for nominal Pb(0.975)Na(0.025)S with 3.0 at. % SrS and CaS, respectively. No deterioration was observed after a 15 d annealing treatment of the samples, indicating the excellent thermal stability for these high performance thermoelectrics. The promising thermoelectric properties of nanostructured PbS point to a robust low cost alternative to other high performance thermoelectric materials.     

Origins of hole doping and relevant optoelectronic properties of wide gap p-type semiconductor, LaCuOSe

LaCuOSe is a wide band gap (～2.8 eV) semiconductor with unique optoelectronic properties, including room-temperature stable excitons, high hole mobility ～8 cm(2)/(Vs), and the capability of high-density hole doping (up to 1.7 × 10(21) cm(-3) using Mg). Moreover, its carrier transport and doping behaviors exhibit nonconventional results, e.g., the hole concentration increases with decreasing temperature and the high hole doping does not correlate with other properties such as optical absorption. Herein, secondary ion mass spectroscopy and photoemission spectroscopy reveal that aliovalent ion substitution of Mg at the La site is not the main source of hole doping and the Fermi level does not shift even in heavily doped LaCuOSe:Mg. As the hole concentration increases, the subgap optical absorption becomes more intense, but the increase in intensity does not correlate quantitatively. Transmission electron microscopy indicates that planar defects composed of Cu and Se deficiencies are easily created in LaCuOSe. These observations can be explained via the existence of a degenerate low-mobility layer and formation of complex Cu and Se vacancy defects with the assistance of generalized gradient approximation band calculations.     

聚磷氮烯及其衍生物电子结构的理论研究

用分子轨道和晶体轨道方法,对聚磷氮烯及其衍生物的电子结构进行了研究,以期更深入地了解聚磷氮烯的结构和性能.研究发现,链状聚磷氮烯和环状三聚磷氮烯为平面结构,其它的环状聚磷氮烯则为巢式结构,吸电子基团取代有使环状聚磷氮烯主链环取平面结构的倾向.研究还发现,无论是链状还是环状聚磷氮烯,都表现为半导体.取代基效应表明,吸电子基团-F和-CN的取代,使聚合物的电子亲和势(EA)和电离能(IP)均增大,能隙减小,给电子基团-CH₃和-OCH₃的取代,使聚合物的IP减少;吸电子基团取代有利于n-型掺杂,给电子基团取代有利于p-型掺杂,但都不改变其半导体的特性.     

Effect of nitrogen and intrinsic defect complexes on conversion efficiency of ZnO for hydrogen generation from water

Band gap narrowing is important for applications of ZnO, especially for photoelectrochemical water splitting. In this work, we carried out first-principles electronic structure calculations with a hybrid density functional on defected ZnO. It is found that nitrogen substitutional doping alone cannot explain the largely enhanced conversion efficiency observed in nitrogen doped ZnO. Instead, complex defects formed by substitutional nitrogen and intrinsic defects play an important role in the band gap narrowing, in agreement with recent experimental results. We propose ZnO fabricated in a Zn-rich environment with heavy nitrogen doping as a photocatalyst for hydrogen generation from water splitting. A method for controlling the band gap of ZnO is also proposed.     

The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.     

Growth of p-type hematite by atomic layer deposition and its utilization for improved solar water splitting

Mg-doped hematite (α-Fe(2)O(3)) was synthesized by atomic layer deposition (ALD). The resulting material was identified as p-type with a hole concentration of ca. 1.7 × 10(15) cm(-3). When grown on n-type hematite, the p-type layer was found to create a built-in field that could be used to assist photoelectrochemical water splitting reactions. A nominal 200 mV turn-on voltage shift toward the cathodic direction was measured, which is comparable to what has been measured using water oxidation catalysts. This result suggests that it is possible to achieve desired energetics for solar water splitting directly on metal oxides through advanced material preparations. Similar approaches may be used to mitigate problems caused by energy mismatch between water redox potentials and the band edges of hematite and many other low-cost metal oxides, enabling practical solar water splitting as a means for solar energy storage.     

Preparation of nanostructure Ni doped CdO thin films by sol gel spin coating method

The nanostructure Ni-doped CdO films have been prepared by sol gel spin coating method. Atomic force microscopy results indicate that the CdO films are formed from the nanoparticles and the grain size is changed with nickel content. X-ray diffraction patterns of the films indicate that the undoped and Ni-doped CdO films have polycrystalline structure with a cubic sodium chloride structure, showing two main characteristic peaks assigned to the (111) and (200) planes. The optical band gap values of undoped and Ni-doped CdO films were determined by optical absorption method. The E_g values of the CdO films were found to be in the range of 2.26–2.60 eV. The E_g values of the CdO films increase with the content of Ni dopant (up to 6% Ni). It is evaluated that the optical band gap and grain size of the CdO film can be controlled by doping with nickel atoms.     

An ambipolar peryleneamidine monoimide-fused polythiophene with narrow band gap

A peryleneamidine monoimide-fused terthiophene with a band gap of 1.4 eV has been synthesized. The donor-acceptor system can be electropolymerized to generate a functionalized polythiophene with a band gap of 0.9 eV and with ambipolar characteristics showing high electroactivity in both the p- and the n-doping process. This is the first example of a p-type conjugated polymer in direct conjugation with n-type perylenemonoimide moieties.     

Band gap anomalies of the ZnM2(III)O4 (M(III)=Co, Rh, Ir) spinels

Development of high figure-of-merit p-type transparent conducting oxides has become a global research goal. ZnM(2)(III)O(4) (M(III) = Co, Rh, Ir) spinels have been identified as potential p-type materials, with ZnIr(2)O(4) reported to be a transparent conducting oxide. In this article the geometry and electronic structure of ZnM(2)(III)O(4) are studied using the Perdew-Purke-Ernzerhof generalized gradient approximation (PBE-GGA) to density functional theory and a hybrid density functional, HSE06. The valence band features of all the spinels indicate that they are not conducive to high p-type ability, as there is insufficient dispersion at the valence band maxima. The trend of increasing band-gap as the atomic number of the M(III) cation increases, as postulated from ligand field theory, is not reproduced by either level of theory, and indeed is not seen experimentally in the literature. GGA underestimates the band-gaps of these materials, while HSE06 severely overestimates the band-gaps. The underestimation (overestimation) of the band-gaps by GGA (HSE06) and the reported transparency of ZnIr(2)O(4) is discussed.     

Dopant ion size and electronic structure effects on transparent conducting oxides. Sc-doped CdO thin films grown by MOCVD

A series of Sc-doped CdO (CSO) thin films have been grown on both amorphous glass and single-crystal MgO(100) substrates at 400 degrees C by MOCVD. Both the experimental data and theoretical calculations indicate that Sc3+ doping shrinks the CdO lattice parameters due to its relatively small six-coordinate ionic radius, 0.89 angstroms, vs 1.09 angstroms for Cd2+. Conductivities as high as 18100 S/cm are achieved for CSO films grown on MgO(100) at a Sc doping level of 1.8 atom %. The CSO thin films exhibit an average transmittance >80% in the visible range. Sc3+ doping widens the optical band gap from 2.7 to 3.4 eV via a Burstein-Moss energy level shift, in agreement with the results of band structure calculations within the sX-LDA (screened-exchange local density approximation) formalism. Epitaxial CSO films on single-crystal MgO(100) exhibit significantly higher mobilities (up to 217 cm2/(V x s)) and carrier concentrations than films on glass, arguing that the epitaxial CSO films possess fewer scattering centers and higher doping efficiencies due to the highly textured microstructure. Finally, the band structure calculations provide a microscopic explanation for the observed dopant size effects on the structural, electronic, and optical properties of CSO.     

Extraordinary Changes in the Electronic Structure and Properties of CdS and ZnS by Anionic Substitution: Cosubstitution of P and Cl in Place of S

Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first‐principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub‐band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co‐substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well.     

表面电荷转移掺杂石墨烯的研究进展

表面电荷转移掺杂是调制石墨烯电学特性的重要手段。发展高效、稳定的表面电荷转移掺杂剂对于提高石墨烯的电学和光电性能、从而推动其在电子和光电领域中的应用具有重要意义。本文围绕高效与稳定两个方面综述了近年来石墨烯表面电荷转移掺杂剂的研究现状以及掺杂石墨烯在光电器件应用方面的进展。根据掺杂剂的类型，着重介绍了最新发展的高效p型和n型掺杂剂，并概述了稳定掺杂方面的重要研究工作。此外，专门介绍了基于掺杂石墨烯透明电极的高性能光电器件。最后，根据表面电荷转移掺杂研究面临的主要挑战，对其未来的发展方向进行了展望。     

聚噻吩取代效应的理论研究

用自洽场晶体轨道法（ＳＣＦ ＣＮＤＯ／２－ＣＯ）对聚噻吩的一些一取代物和二取代物的电子结构进行了研究，计算的取代基包括－ＣＨ３，－Ｃ２Ｈ５，－ＯＣＨ３和－ＣＮ。计算结果表明，这些取代基基本没有影响聚噻吩主链的平面结构，除聚－３，４－二甲基噻吩的主链发生了４０°的扭转外，其它衍生物的主链仍处于同一平面。根据各取代高分子的电子特性我们得到结论：给电子基团和吸电子基团的取代教师将使能隙（Ｅｇ）减小，价带