Mn、Li共掺ZnO稀磁半导体的制备与铁磁性研究

采用固相陶瓷烧结法制备了Mn、Li共掺的ZnO稀磁半导体材料,实现了室温铁磁性。分别用XRD、XPS和VSM对各样品进行了结构测量和磁性能测量,分析了Mn、Li掺杂浓度对ZnO基稀磁半导体的影响。结果表明,在相同的外磁场下,随着Mn掺杂浓度的增加,陶瓷的磁化强度增大。但较高的Li掺杂浓度可能会形成更多填隙离子,减少空穴浓度,最终使材料的室温铁磁性变差。     

Cu掺杂ZnO纳米粒子的光学性能及铁磁性

利用溶胶凝胶法制备了纳米结构的Cu掺杂ZnO基稀磁半导体,通过X射线衍射分析表明,样品为纯相ZnO纤锌矿结构,磁性测量表明样品在室温下呈室温铁磁性,铁磁性来源为氧化锌晶格中的缺陷与Cu2+离子之间的交换作用。室温光致发光(PL)谱观察到紫外带边和可见光区两个发射峰,且随着Cu掺杂量增加,紫外峰淬灭,可见峰发射增强。     

稀磁半导体Zn_（1-x）Ni_xO,Zn_（1-2x）Mn_xNi_xO及Zn_（1-2x）Co_xNi_xO纳米晶体的制备与磁性研究

利用溶胶-凝胶法制备了一系列的稀磁半导体材料如Zn1-xNixO、n1-2xMnxNixO及Zn1-2xCoxNixO晶体粉末,通过震荡样品磁强计（VSM）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）和能量色散谱（EDS）分别对样品的磁性、晶相结构、形貌和成分进行了表征分析,讨论了获得本征铁磁性Zn1-xNixO样品的制备条件,比较了Mn、Co共掺杂对Zn1-xNixO磁性的影响,给出了Ni在ZnO中的固溶度以及实际掺杂浓度与名义掺杂浓度的关系。     

流变相反应法合成Zn_(1-x)Co_xO室温稀磁半导体

利用流变相反应法制备得到Zn1-xCoxO(x=0.02、0.04、0.06、0.08)稀磁半导体材料。X射线衍射分析,发现Co的掺杂并未改变ZnO的纤锌矿结构,并没有杂质相的生成,衍射峰的峰位随着Co掺杂向高角度移动,Co已进入ZnO晶格。电镜及吸收光谱进一步表明样品中没有第二相的出现,Co2+成功掺入ZnO晶格。采用超导量子干涉磁强仪测量Zn0.96Co0.04O的磁性,样品在300K存在明显的磁饱和现象和磁滞回线,表明具有室温下铁磁性,其磁性来源可以用束缚磁极化子(BMPs)模型解释。     

自燃烧法合成的ZnO基稀磁半导体纳米颗粒研究进展

稀磁半导体制备方法与磁性起源的研究是当前凝聚态物理的一项热门课题.首先介绍了自燃烧合成法的原理和优点,然后以Co和Mn掺杂ZnO为重点,总结了国内外采用自燃烧法合成的ZnO基稀磁半导体纳米颗粒晶体结构、磁性能相关的研究进展,讨论了所得纳米颗粒磁性能的内在物理机制.通过对自燃烧法合成的更宽掺杂范围ZnO基稀磁半导体纳米颗粒的研究,使我们能够更加系统地了解过渡金属掺杂ZnO材料的结构与磁性能,并探讨所得实验现象的内在物理机制.     

水热法制备的Ti1-xCoxO2稀磁半导体特性

采用水热法制备出Ti1-xCoxO2(x=0～0.10)稀磁半导体材料,并对其形貌、结构及磁性能进行表征.X射线衍射分析结果表明,纯TiO2样品为锐钛矿相,掺杂Co离子后样品中出现金红石相,当掺杂浓度到0.10时样品中出现Co3O4的衍射峰.透射电镜和X射线能量色散谱测试结果表明,样品形貌规整,平均粒径约为20nm,并且证实样品中含有Co元素.利用振动样品磁强计对其磁性进行测量,结果表明样品在室温条件下存在铁磁性.     

Bi系Co基氧化物热电材料制备及结构替代研究

采用常压固相烧结法制备Bi2SrCaCo2Oδ和Bi2Ca2Co2Oδ氧化物热电材料,研究Sr、Ca位替代或掺杂对陶瓷材料制备条件、晶体结构和电学性能的影响.通过XRD、SEM、EDS等表征技术及标准四探针法研究了烧结温度和晶体结构参数对陶瓷物相、显微组织形貌和电学性能的影响.结果表明同族元素Ca、Sr的互相替代,Bi...     

脉冲激光沉积制备Co掺杂ZnO薄膜的磁学性质研究

采用脉冲激光沉积的方法, 利用Zn_0.95Co_0.05O陶瓷靶, 在不同氧气压力下制备Zn_1-xCo_xO薄膜. 利用X射线衍射(XRD)、电子探针、吸收光谱对薄膜中Co含量、Co²⁺离子比例以及相组成进行了定量分析, 研究了沉积过程中氧气压力对薄膜中Co含量的影响, 定量讨论了薄膜中Co含量、Co²⁺离子比例以及相组成与薄膜室温磁性之间的关系, 分析了薄膜磁性的起源. 分析结果表明: 薄膜中Co含量随氧气压力增大而减少, Co以替位Co²⁺离子为主. 精细XRD分析表明, 薄膜中存在纳米尺度的金属Co团簇, 其含量与薄膜室温磁性估计的结果一致, Zn_1-xCo_xO薄膜的室温磁性归因于金属Co纳米团簇的超顺磁磁化机制.     

RSn3-xCox(R=Nd,Sm)系列化合物的结构及磁性能研究

系统地研究了新型稀土-半导体-磁性金属所组成的RSn3-xCox(R=Nd,Sm;x=0~0.3)系列的制备、晶体结构以及磁性。研究表明:RSn3-xCox具有AuCu3型立方结构,空间群Pm3m,稀土原子占据1a晶位,Sn占据3c晶位,Co部分替代Sn占据3c晶位。点阵常数与晶胞体积常数随Co掺杂量的增加而减小。其磁性变化与Co含量密切相关,随着Co含量的增加,稀土半导体化合物中产生铁磁性相,在Sm-Sn-Co体系中SmSn2.8Co0.2呈现混合磁性、SmSn2.7Co0.3呈现铁磁性,这有别于纯RSn3系列的磁性(低温反铁磁型和室温的顺磁性),为这类稀土半导体化合物作为新型磁电子材料的潜在应用提供了可能性。     

均相沉淀法制备Co3O4纳米颗粒及磁性研究

以Co（NO3）2·6H2O和（NH2）2CO为原料,在不引入高分子分散剂的条件下,采用均相沉淀法制备Co3O4纳米颗粒。用TGA、DSC、XRD研究了目标产物的前驱体及其分解过程,结果表明：Co3O4在焙烧阶段形成。Co3O4纳米颗粒结构、形貌、粒径分布和磁性能分别用XRD、TEM、粒径分析仪、VSM表征,Co3O4纳米颗粒平均粒径约为21nm,粒径分布均匀。5K时产物表现为铁磁性,矫顽力Hc=580Oe。     

Effect of additional Zn<Superscript>2+</Superscript> dopant on the ferromagnetic properties of Co-doped CeO<Subscript>2</Subscript> nanoparticles prepared by sol–gel method

Effect of additional Zn²⁺ dopant on the ferromagnetism (FM) of Co doped CeO₂ nanoparticles was studied. The Zn and Co co-doped CeO₂ nanoparticles (Ce_0.97?xZn _x Co_0.03O₂: where x?=?0, 0.01, 0.03, 0.05) were prepared by sol–gel technique. The crystal structure, morphology, and magnetic properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman) and physical property measurement system (PPMS). XRD and Raman studied showed that certain amount of Zn²⁺ can readily be incorporated into the lattice of Co doped CeO₂ with single-phase of CeO₂ original cubic fluorite crystal structure, and no ferromagnetic secondary phase was observed. SEM images show Zn and Co co-doped CeO₂ nanoparticles were spherical and uniform size. The PPMS studied indicate that the room-temperature FM of Co doped CeO₂ nanoparticles increase with additional Zn²⁺ dopant. This result is helpful in understanding the origin of FM in diluted magnetic oxides (DMO) as well as improving the magnetic property of DMO.     

Signature of room temperature ferromagnetism in Mn doped CeO2 nanoparticles

We report structural and magnetic properties of Mn doped CeO₂ nanoparticles using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM) and dc magnetization measurements. XRD results infer that all the samples have single phase nature and lattice parameters decrease with Mn doping. The particle size calculated using XRD and TEM analysis was found to decrease with Mn doping. Field cooled magnetization measurement shows that the transition temperature is above room temperature. Magnetic hysteresis loop studies indicate that undoped and Mn doped CeO₂ nanoparticles show weak ferromagnetic behavior at room temperature.     

Room temperature ferromagnetism in Ni doped In2O3 nanoparticles

In the present work, Ni doped In₂O₃ nanoparticles were prepared using simple co-precipitation method. From the x-ray diffraction analysis it is observed that all samples exhibit single phase polycrystalline nature. All the diffraction lines correspond to the bixbyite type cubic structure. A UV visible analysis reveals that optical band gap decreases from 4.63 to 3.84 eV with Ni doping. DC magnetization measurements reveal that Ni doped In₂O₃ nanoparticles exhibit room temperature ferromagnetism.     

Bi2Te3纳米结构的制备、磁性掺杂和结构表征

通过液相法制备Bi2Te3纳米管,设计并优化了Co离子的掺磁方案。通过扫描电镜、透射电镜、X射线衍射、红外光谱和能量色散X射线光谱对制备的样品进行了结构表征。实验结果表明,液相法可制备出晶相良好的Bi2Te3纳米管、Co离子均匀掺杂的Bi2Te3纳米结构样品。     

Preparation of CeO2 novel sponge-like rods by emulsion liquid membrane system and its catalytic oxidation property

CeO₂ sponge-like rods aggregated by small nanoparticles in the diameter range of 14-31 nm, with diameters of 170-810 nm and lengths of 5-10 μm, which were successfully fabricated through a route of liquid emulsion membrane followed by heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) were employed to characterize the samples. The catalysts were tested for CO oxidation, and an enhanced catalytic activity has been found for CO oxidation by using CeO₂ sponge-like rods as compared with CeO₂ nanorods and nanoparticles, which showed that the morphology of CeO₂ crystalline plays an important role in determining their catalytic oxidation property.     

Presence of intrinsic defects and transition from diamagnetic to ferromagnetic state in Co<Superscript>2+</Superscript> ions doped ZnO nanoparticles

In this paper, we report the structural, morphological and magnetic properties of pure and Co²⁺ doped ZnO nanoparticles synthesized using sol–gel auto combustion method. The prepared nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction pattern (SAED), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. The analysis of XRD pattern shows the single phase nature with a hexagonal wurtzite structure for the prepared nanoparticles. The average crystallite sizes of the prepared nanoparticles were found in the range 18–19 nm. SEM images showed that pure and Co²⁺ doped nanoparticles have different morphology. The shape of the prepared nanoparticles is approximately hexagonal shown by TEM image. SAED pattern also confirms the wurtzite structure with single crystalline nature. FTIR spectra showed the characteristic vibrations frequency band of Zn–O. Photo luminescence spectrum showed that two emission peaks, which are ascribed to near band edge transitions and broadened intensive green emission associated with oxygen-vacancy defects. The magnetic properties were measured by vibrating sample magnetometer (VSM) and superconducting quantum interference device with field dependant magnetization at 300 K and temperature dependant magnetization from 0 to 300 K. From VSM analysis, pure ZnO nanoparticles show diamagnetic behavior while Co²⁺ doped ZnO nanoparticles revealed ferromagnetic behaviour at room temperature. The significant changes in M–H loop from diamagnetic behavior to ferromagnetic behavior are due to the intrinsic defects such as oxygen vacancies (Vo) and zinc vacancies (Vz_n). The RTFM has been presented in terms of vacancies in the frame of bound magnetic polaron model.     

Magnetic properties of (Co,Al) co-doped SnO<Subscript>2</Subscript> nanoparticles

The desired size of pure SnO₂ and Co (1, 3, 5 mol%) with constant 5 mol% of Al co-doped into SnO₂ nanoparticles are synthesized by chemical co-precipitation method. The raw materials used in synthesis are SnCl₂.2H₂O, AlCl₃, Co (C₂H₃O₂).4H₂O, aqueous NH₄OH and Polyethyleneglycol (PEG) from AR grade. The XRD pattern of pure and co-doped samples confirm the formation of tetragonal rutile phase of SnO₂ nanoparticles with average particle size 25 and 20 nm respectively. Micrographs of scanning electron microscope (SEM) for pure and (Co, Al) co-doped into SnO₂ show that the prepared nanoparticles are agglomerate and spherical in shape. The EDAX spectra of prepared nanoparticles indicate the presence of Co²⁺, Al³⁺, Sn⁴⁺ and O²⁺ and also confirm stoichiometric proportions of raw material in the formation of SnO₂. Transmission electron microscope (TEM) reveals that the surface morphology of pure and co-doped samples are spherical, and average size of particles is ~20 nm. Magnetization measurements from M-H curves of VSM show that the ferromagnetism at low concentration of Co and at higher concentration of Co shows weak ferromagnetism due to super exchange coupling among neighboring ions. The bound magnetic polarons model supports the observed ferromagnetic behavior.     

Preparation and doping modification of cerium oxide photosensitizers applied to photosensitive glass ceramics

CeO₂ nanoparticles doped with different types of Pr, Y, W and CaF₂ are prepared via a facile one-pot combustion method. Their crystallinity, particle size and absorption spectrum are investigated by X-ray diffraction (XRD), grading analysis and ultraviolet–visible spectroscopy (UV–Vis) absorption spectrum. Among the doped samples, W-doped CeO₂ (Ce_0.9W_0.1O₂) is selected out, which exhibits obvious red-shift of the absorption band as compared with the undoped CeO₂, achieving good match between the ceria absorption peak and the industrial 365 nm light source. Consequently, under the 365 nm exposure, the W-doped CeO₂ show more efficient reduction ability for Ag⁺ to Ag. The results indicate that W-doped CeO₂ is a very promising photosensitizer for photosensitive glass ceramics under industrial 365 nm light exposure, which can better absorb photons under UV light and then reduce Ag⁺ to elemental Ag.

     

Current-voltage characteristics and grain growth of Li2CO3-doped tungsten trioxide ceramics

Ceramics samples of tungsten trioxide doped with lithium carbonate from 0.5 to 5 mol% were prepared by conventional electroceramic technique. The current-voltage characteristics of these ceramics were measured under various ambient temperatures. All of the I-V curves showed non-ohmic electrical properties with obvious negative-resistance characteristic at room temperature. It is found that there exists a direct correlation between the negative-resistance phenomenon in the I-V curves and the electrical history of these samples. The suitability of some models regarding the negative-resistance characteristics is discussed. X-ray diffraction (XRD) revealed coexistence of two phases of tungsten trioxide, which depends on the amount of lithium. Scanning electron microscope (SEM) showed great differences for both grain shape and size between the Li-doped and undoped WO₃ ceramics, and this indicates that Li₂CO₃ doped into WO₃ influences strongly the growing of WO₃ during sintering process.