Sb、Sm共掺杂SnO2的电子结构与光学性质第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,构建了Sm、Sb及Sm和Sb共掺杂SnO₂超晶胞模型,研究了经过几何优化后的各掺杂体系的焓变值、能带结构、态密度、电荷布居、介电常数、吸收系数、反射率等光电性质.结果表明：Sm和Sb的掺杂可以有效地提升SnO₂的导电性能,且Sb和Sm共掺杂体系的电学性能最佳. Sm和Sb掺杂还可以增加SnO₂在红外波段的电子极化能力和电子跃迁概率,提升了红外反射率,且共掺杂体系的电子束缚能力最强、反射率最高.这为SnO₂基光电材料的研制提供了一定的理论依据.     

Structural,electrical and magnetic properties of (Fe,Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

Nanostructures (NSs) of basic composition Sn_1−xFe_x/2Co_x/2O₂ with x=0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO₂, the other three weak Raman peaks at about 505, 537 and 688 cm⁻¹ were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M–H curves of Fe and Co co-doped SnO₂ NSs. However, pure SnO₂ nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.     

Ag-Cr共掺LiZnP新型稀磁半导体的光电性质

采用基于密度泛函理论的第一性原理平面波超软赝势法,对纯Li Zn P, Ag/Cr单掺和Ag-Cr共掺Li Zn P新型稀磁半导体进行了结构优化,计算并分析了掺杂体系的电子结构、磁性、形成能、差分电荷密度和光学性质.结果表明:非磁性元素Ag单掺后,材料表现为金属顺磁性;磁性元素Cr单掺后, sp-d杂化使态密度峰出现劈裂,体系变成金属铁磁性;而Ag-Cr共掺后,其性质与Ag和Cr单掺完全不同,变为半金属铁磁性,带隙值略微减小,导电能力增强,同时形成能降低,原子间的相互作用和键强度增强,晶胞的稳定性增强.通过比较光学性质发现,掺杂体系的介电函数虚部和光吸收谱在低能区均出现新的峰值,且当Ag-Cr共掺时介电峰峰值最高,同时复折射率函数在低能区发生明显变化,吸收边向低能方向延展,体系对低频电磁波吸收加强.     

Study on the ferromagnetism in Co and N doped ZnO thin films

Present investigation reports the structural, optical and magnetic properties of co-doping of Co and N ions in ZnO samples, prepared by two distinct methods. In the first method, samples are synthesized by Sol–gel technique in which the Co and N are co-doped simultaneously during the growth process itself. In the second case, N ions are implanted in the Co doped ZnO thin films grown by Pulsed Laser Deposition (PLD). Structural studies showed that the nitrogen implantation on Co doped ZnO samples developed compressive stress in the films. X-ray photoelectron spectroscopy confirmed the doping of Co and N in ZnO matrix. In the Resonant Raman scattering multiple LO phonons up to fifth order are observed in the (Co, N) co-doped ZnO. Photoluminescence spectra showed that there is reduction in the bandgap due to the presence of Co in the lattice and also the presence of Zn vacancies in the films. All samples showed ferromagnetic behavior at room temperature. The magnetic moment observed in the implanted films is found to be varied with the different dosages of the implanted N ions. First principle calculations have been carried out to study the possible magnetic interaction in the co-doped system. Present study shows that the ferromagnetic interaction is due to the hybridization between N 2p and Co 3d states in the (Co, N) co-doped ZnO and is very sensitive to the geometrical configurations of dopants and the vacancy in the ZnO host lattice.     

Mg-F受主-施主共掺SnO_2的第一性原理研究

利用基于密度泛函理论(DFT)的第一性原理平面波赝势法,研究了Mg-F受主-施主共掺杂SnO_2的结构稳定性、能带结构、态密度及布居分布.结果表明,Mg-F掺杂能形成稳定的掺杂体系,在价带顶附近F 2p的态密度峰值强度较大,Mg-F原子之间杂化强,引入施主掺杂元素F有利于Mg受主掺杂的稳定性,同时Mg-O之间电子重叠布居值增大,原子之间的重叠增加,共有化增强,可使导电性能进一步提升.     

Reduced conductivity and enhancement of Debye orientational polarization in lanthanum doped cobalt ferrite nanoparticles

In this work we have investigated the conductivity and dielectric properties of CoLa_xFe_2−xO₄ (x=0.0, 0.03, 0.05, and 0.07) nanoparticles synthesized by chemical co-precipitation route. X-ray diffraction analysis confirms the inverse spinal structure of nanoparticles with slight increase in the lattice constant as La concentration increases. Transmission electron microscopy shows spherical nanoparticles with sizes of ∼20 nm. Impedance spectroscopy of the samples was performed in the frequency range 20 Hz-2 MHz at room temperature. The resistance of the grains and grain boundaries was found to increase with lanthanum concentration while the AC conductivity of the samples was observed to decrease with increasing La concentration. Dipolar orientational polarization was found to play an important role in determining dielectric properties of the samples.     

Local structure investigation of (Co,Cu) co-doped ZnO nanocrystals and its correlation with magnetic properties

Pure, Co doped and (Co, Cu) co-doped ZnO nanocrystals have been prepared by wet chemical route at room temperature to investigate the effect of Cu doping in Co doped ZnO nanocrystals . The nanocrystals have initially been characterized by X-ray diffraction, FTIR, Raman, optical absorption and EPR spectroscopy and the results were corroborated with DFT based electronic structure calculations. Magnetic properties of the samples have been investigated by studying their magnetic hysteresis behavior and temperature dependence of susceptibilities. Finally the local structure at the host and dopant sites of the nanocrystals have been investigated by Zn, Co and Cu K edges EXAFS measurements with synchrotron radiation to explain their experimentally observed magnetic properties.     

Ce、Ga、La掺杂二维SnO2电子结构及光电性质的第一性原理研究

二维材料具有优异的光学、力学、热学、磁学等性质,成为研究的热点之一. SnO₂薄膜中的电子迁移率非常高,兼具透明和良好的导电性能,是一种性能绝佳的半导体材料.本文用密度泛函理论框架下的第一性原理研究了二维SnO₂及其掺杂体系的电子结构、电子态密度、导电性能及光学性质,计算结果表明：相比较于三维SnO₂,二维SnO₂的费米能级附近产生很多杂质能级,提高了载流子浓度,带隙明显变窄,电子的局域性增强,导带中电子的有效质量增加了,电子跃迁更容易发生,增加了材料的导电性能;二维SnO₂比三维SnO₂材料的电极化能力强,在红外区、可见光区、紫外区域的光子吸收性能更优异,光电导率更高,更有利于光生电子-空穴对的分离和迁移,即可以有效地提高其光电转换效率,其中掺杂La元素能更好地提高在红外区、可见光区及紫外区吸收光子的能力,更有利于光电转换的效率,提高导电性.     

磁控溅射法制备钴掺杂氧化锌薄膜室温磁学性质

钴掺杂氧化锌是室温稀磁半导体的重要候选材料,其磁学特性和钴掺杂浓度、显微结构及光学性质密切相关。磁控溅射具有成本低、易于大面积沉积高质量薄膜等特点,是广受关注的稀磁半导体薄膜制备方法。利用磁控溅射方法制备了不同浓度的钴掺杂氧化锌薄膜,并对其显微结构、光学性质和磁学特性进行了系统分析。结果表明:当掺杂原子分数在8%以内时,钴掺杂氧化锌薄膜保持单一的铅锌矿晶体结构,钴元素完全溶解在氧化锌晶格之中;薄膜在可见光区域有很高的透射率,但在567, 615和659 nm处有明显吸收峰,这些吸收峰源于Co2+处于O2-形成的四面体晶体场中的特征d-d跃迁。磁学特性测试结果表明钴掺杂氧化锌薄膜具有室温铁磁性,且钴的掺杂浓度对薄膜的磁学特性有重要影响。结合薄膜结构、光学和电学性质分析,实验中观察到的室温铁磁性应源于钴掺杂氧化锌薄膜的本征属性,其铁磁耦合机理可由束缚磁极化子模型进行解释。     

Optical and electrical properties of undoped and (Mn, Co) co-doped ZnO nanoparticles synthesized by DC thermal plasma method

The undoped and (Mn, Co) co-doped ZnO nanopowders were synthesized through DC thermal plasma method. The pellets of this powder were annealed at 450, 550 and 650 °C for 1 h. Structural, chemical and optical properties of the samples were studied by XRD, SEM, EDX, UV–Vis and PL analysis. XRD spectra showed that all the samples were hexagonal wurtzite structure and as the annealing temperature increases the material becomes purer and more crystalline. It is seen that the optical band gap decreases when the ZnO is doped with manganese and cobalt. Photoluminescence intensity varies with doping because of the increment of oxygen vacancies. DC conductivity studies of the pellets were carried out at different temperatures (25–100 °C) and it was found that the activation energy for the electrical transport is high for (Mn, Co) co-doped ZnO than undoped ZnO.     

AgSnO2触头材料在Ni-S共掺杂下的第一原理性计算

该研究采用掺杂的方式对SnO₂的导电性能进行改良,基于密度泛函理论的第一性原理,运用CASTEP软件对单掺杂Ni-SnO₂、S-SnO₂和共掺杂Ni-S-SnO₂的晶格参数、能带结构、电子态密度进行了计算,并对其电荷布居进行了分析.结果表明：S单掺杂时,晶胞体积略微增大;Ni单掺杂时,晶胞体积略微减小;而Ni-S共掺杂时,晶胞体积略微增大但增大幅度小于S单掺杂时的晶胞体积.与未掺杂相比,掺杂使得晶胞禁带减小、杂质能级增多、电子跃迁能减小,使其导电性增强,同时,掺杂使得费米能级附近峰值减小,局域性下降,原子间成键更强,材料更稳定.     

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu₃Ti₄O₁₂ (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.     

Effect of Gd3+ doping on structural,optical and frequency-dependent dielectric response properties of pseudo-cubic BaTiO3 nanostructures

We report on the structural, optical and dielectric characterization of solid state derived, pseudo-cubic nanoscale barium titanates (BTs) with gadolinium (Gd³⁺) as substitutional dopant. Referring to X-ray diffractograms, apart from the BT peaks related to perovskite structure, the non-existence of any additional peaks due to byproducts has revealed that Gd³⁺ has undergone substitutional doping into the BT host lattice. The well-separated BT nanoparticles of typical size ～10–15 nm were observed through electron microscopy studies. Following a direct, allowed type carrier transition (n=1/2), a reduction in the optical band gap value (from 3.28 to 3.255 eV) was observed when the Gd-doping level was varied within 0–7 %. Conversely, the Urbach energy followed an increasing trend, from a value of 0.741 to 1.879 eV. Furthermore, the dielectric constant showed a decreasing tendency with doping content and with increasing frequency. However, in the low-frequency region, the loss tangent (tanδ), which is the combined result of orientational polarization and electrical conduction, was found to be quite high in the doped samples as compared to their un-doped counterpart. The frequency-dependent electrical data were also analyzed in the framework of conductivity and impedance formalisms. In particular, the ac conductivity which varies as ～ω ^s approaches ideal Debye behavior (s→1) for a low Gd level and a higher doping concentration did not show improved dielectric feature of the host. The incorporation of rare-earth (Gd³⁺) ions into the BT host system could greatly manifest dielectric relaxation and carrier conduction mechanisms, in a given frequency range, and thus can find immense scope in miniaturized nanoelectronic elements including ceramic capacitors and transducers.     

Influence of dopant level on structural, optical and magnetic properties of Co-doped anatase TiO2 nanoparticles

Cobalt-doped TiO₂ nanoparticles were synthesized by sol-gel method. The associated structural, optical, compositional and magnetic properties of the nanoparticles as a function of cobalt concentration have been systematically studied. The X-ray powder diffraction reveals that all samples have pure anatase phase tetragonal system and the lattice parameter analysis indicated that Co ions may substitute into the lattice of TiO₂. The average particle size is 15 nm, when found through transmission electron microscope. Optical spectroscopy measurement showed that the bandgap value decreases upon increasing Co concentration. The magnetic measurements revealed that the enhanced room temperature ferromagnetism (RTFM) strongly depends on the doping content.     

Enhanced magnetization in Co and Ta-substituted BiFeO3 ceramics

Cobalt (Co) and tantalum (Ta) co-substituted BiFeO₃ polycrystalline ceramics were prepared by a solid-state reaction and their magnetic and dielectric properties were investigated. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. The co-substitution decreased the electrical conductivity by six orders of magnitude along with the reduction of grain size. The magnetoelectric coupling was estimated in co-substituted BiFeO₃ by determining the changes of the dielectric constant with an external magnetic field.     

Effect of Fe/Pb molar ratio on the structure,magnetic and dielectric properties of PbFe12O19 nanoparticles

In this paper, lead hexaferrite (PbFe₁₂O₁₉) nanoparticles were synthesized by sol-gel method. In order to prepare PbFe₁₂O₁₉ nanoparticles, the metal nitrates with Fe/Pb?=?8, 10, 11, 12, 14 ratios and citric acid were used. The structure, morphology, magnetic, and dielectric properties of PbFe₁₂O₁₉ nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM) and LCR meter. XRD results revealed that the samples with Fe/Pb?≤?10 and Fe/Pb?>?10 have single-phase hexaferrite and hematite (α- Fe₂O₃) structures, respectively. As a result, the sample with Fe/Pb?=?10 is single-phase and shows the highest values of the saturation magnetization and remanence magnetization. We found that the values of dielectric constant (ε′) and dielectric loss (ε″) increase with an increase in the Fe/Pb molar ratio from 8 to 12 and then decreases with an increase of Fe/Pb molar ratio to 14. The variation of ac conductivity (σ_ac) with frequency ranging from 1?kHz to 200?kHz showed that electrical conductivity in these ferrites is mainly due to the electron hopping mechanism.     

Improvement of sintering,nonlinear electrical,and dielectric properties of ZnO-based varistors doped with TiO_2

The effects of TiO_2 on sintering and nonlinear electrical properties of(98.5-x)ZnO–0.5MnO_2–0.5Co_2O_3-0.5Bi_2O_(3–x)TiO_2(x = 0.3,0.5,0.7,0.9 mol%) ceramic varistors prepared by the ceramic technique are investigated in this work.The optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption percentages.The optimum sintering temperature is found to be 1200℃,at which each of the samples shows a maximum firing shrinkage and minimum water absorption.Also minimum water absorption appears in a sample of x = 0.9 mol%.Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase sintering.The crystal size of ZnO decreases with increasing TiO_2 doping.The addition of TiO_2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO_2,further addition negatively affects it.A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz–200 kHz.The temperature and composition dependences of the dielectric constant and AC conductivity are also studied.The increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency.     

Sb掺杂对透明SnO_2薄膜导电性能影响的第一性原理计算(英文)

本文根据密度泛函理论(DFT),采用第一性原理平面波赝势方法,计算了Sb掺杂对透明导电薄膜SnO2电子结构及导电性能的影响,讨论了掺杂下SnO2晶体的结构变化、能带结构、电子态密度.计算结果表明,Sb掺杂的SnO2具有高的电导率,且随着掺杂浓度的增加,能带简并化加剧,浅施主杂质能级向远离导带底方向移动.     

新型稀磁半导体Fe掺杂LiZnP的光电性质

采用基于密度泛函理论的第一性原理计算法研究了新型稀磁半导体Li_(1±)_y(Zn_(1-)_xFe_x)P (x=0, 0.0625;y=0, 0.0625)的电子结构、磁性及光学性质.结果表明,Fe的掺入使体系产生自旋极化杂质带,Fe的3d态与Li2s态,Zn4s态以及P3p态的态密度峰在费米能级处出现重叠,产生sp-d轨道杂化,此时体系净磁矩最大,材料表现出金属性,导电性增强.当Li空位时,导电性减弱,但杂质带宽度最大,居里温度最高.而Li填隙时,体系形成能最低,材料变为半金属性,表现为100%自旋注入,表明掺杂体系的磁性和电性可以分别通过Fe的掺入和Li的含量进行调控.对比光学性质发现,Li空位时,在介电函数虚部和复折射率函数的低能区出现新峰,扩大了对低频电磁波的吸收范围.能量损失函数表明掺杂体系具有明显的蓝移效应,且Li填隙时有更强的等离子共振频率.     

磁性和非磁性元素掺杂的自旋梯状化合物Sr_(14)(Cu_(0.97)M_(0.03))_(24)O_(41)(M=Zn,Ni,Co)的结构和电输运性质

利用固相反应法制备了Sr14Cu24O41及其系列B位掺杂Sr14(Cu0.97M0.03)24O41(M=Zn,Ni,Co)的样品.X射线衍射分析显示,所有样品均为纯相,晶格常数a与c没有明显的变化;Zn掺杂样品晶格常数b没有明显变化,而Ni,Co掺杂样品晶格常数b分别稍有增加.选区电子衍射研究揭示:磁性元素Ni,Co及非磁性元素Zn掺杂,可能主要替代了Sr14Cu24O41结构中自旋链上的Cu原子,从而影响了自旋链上的dimer排列,破坏电荷有序超结构.电输运测量显示:Zn2+,Ni2+,Co3+离子掺杂样品的电阻率降低,但仍体现半导体行为,所有的掺杂样品都存在一个渡越温度Tρ,当TTρ时,其导电机理是以单空穴热激发导电占主要地位,在TTρ时,配对的局域化空穴的一维变程跳跃导电占主要优势;在相同的掺杂量下,非磁性元素Zn掺杂对电阻率值的影响大于磁性元素Ni,Co掺杂的影响,而磁性元素Ni,Co掺杂对渡越温度Tρ的影响大于非磁性元素Zn掺杂的影响.