钙钛矿型纳米BaFeO3的制备、结构表征及铁磁性研究

采用溶胶-凝胶法制备出钙钛矿型纳米BaFeO3粉末,利用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析研究了其微观结构及形貌,结果表明:胶体试样经800℃退火处理后,形成了20nm左右的钙钛矿型BaFeO3粉末,其(110)面晶面间距为0.280nm左右,(100)面晶面间距为0.401nm左右.利用振动样品磁强计(VSM)研究了纳米BaFeO3粉末的室温铁磁性能,测量结果表明:在室温条件下,纳米BaFeO3粉末具有完整闭合的磁滞回线,具有较小的矫顽力和较低的饱和磁化强度,呈现出明显的弱铁磁性,且铁磁性随退火温度的变化明显.钙钛矿型纳米BaFeO3的铁磁性主要归因于Fe3 _O_Fe4 之间的氧空位.     

BiFeO3纳米粉的制备、结构表征及铁磁特性

采用溶胶-凝胶法成功地制备出BiFeO₃纳米粉,利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）测量分析了其结构与形貌,结果发现：胶体经700℃烧结2—25 h后,形成了30 nm左右的较纯相BiFeO₃粉末,该样品为六角晶系,R3-m［166］空间群,晶胞参数为a=b=05580 nm,c=06939 nm,其（101）面晶面间距为0396 nm左右,（ 关键词： 溶胶-凝胶法 3纳米粉')" href="#">BiFeO₃纳米粉 结构表征 铁磁特性     

单相Bi0.9Ba0.1Fe0.85Mn0.15O3陶瓷中的多铁性

溶胶-凝胶法制备了Bi_0.9Ba_0.1Fe_0.85Mn_0.15O₃陶瓷样品,XRD分析显示其为单相菱方钙钛矿结构,明显的磁滞回线和电滞回线说明其在室温具有弱铁磁性和铁电性,介电常数随外磁场的变化显示双掺样品具有更大的磁容效应. 关键词： 溶胶-凝胶法 多铁材料 磁容效应     

纳米ZnO和ZnO-SiO2复合薄膜的光学性质研究

通过溶胶凝胶(sol-gel)法分别在玻璃衬底上制备了ZnO纳米薄膜和ZnO-SiO₂纳米复合薄膜,并利用紫外-可见光分光光度计对薄膜的光学性能进行了分析.可见光-紫外透射谱显示,随着ZnO溶胶浓度从0.7mol/L降低到0.006mol/L,制备的ZnO薄膜从只出现一个380nm(对应的光学禁带宽度为3.27eV)左右的吸收边到在380和320nm(对应的光学禁带宽度为3.76eV)左右各出现一个吸收边,并且随着ZnO溶胶浓度的降低,在380—320nm波段内的透过率明显提高.而Z 关键词： 纳米ZnO 2复合薄膜')" href="#">ZnO-SiO₂复合薄膜 溶胶凝胶法 透射率     

CoxTi1－xO2－δ体材中氢退火引起的铁磁性及结构相变

利用固相反应法在700℃—1000℃不同的温度下、空气中烧结Co₃O₄ 和TiO₂混合物，制备了(Co₃O₄)_x/3(TiO2)_1-x(03，说明Co₃O₄与TiO₂反应形成了CoT iO₃；同时，在700 ℃低温和900 ℃以上的高温烧结样品中分别观察到了单相的 锐钛矿和金红石相结构.经高低温烧结的样品在500 ℃氢退火后，CoTiO₃相消失 ，锐钛矿相的Co_xTi_1-xO_2-δ形成.X射线光电子能谱(X PS)分析显示，氢退火样品中的Co以+2氧化价态存在，同时没有观察到金属态的Co，这说明 氢退火样品中的室温铁磁性不是源于金属Co颗粒的形成，而是与钙钛矿结构的CoTiO_{3< /sub>相的消失和锐钛矿型的CoxTi1-xO2-δ相的形成 有关.(Co3O4)x/3(TiO2)1-x( 0x}Ti_1-xO_2-δ相的本征铁磁性，伴随着结构相变而产生的Co离子之间的铁磁交换相互作用或 许是样品室温铁磁性产生的根本原因. 关键词： 室温铁磁性 结构相变 锐钛矿 氢退火     

(Fe1-xCox)3BO5纳米棒磁性的研究

本文采用高温有机溶剂法制备了(Fe_1-xCo_x)₃BO₅纳米棒, 通过控制反应物中乙酰丙酮钴的含量合成了不同Co含量的(Fe_1-xCo_x)₃BO₅. 利用高分辨透射电子显微镜(HRTEM)、超导量子干涉磁强计(SQUID)对其形貌和磁性能进行了表征. 高分辨透射电子显微镜结果表明制备出的纳米(Fe_1-xCo_x)₃BO₅为多晶棒状, 且具有多折孪晶结构; 磁性测量的结果表明,(Fe_1-xCo_x)₃BO₅纳米棒在室温下表现出铁磁性, 随着Co含量的增加, 纳米棒的铁磁性逐渐增加, 该纳米棒有望用来研究生物大分子的机械性能.     

掺纳米锗氧化硅的发光性能研究

由溶胶/凝胶法制备得到的GeO₂/SiO₂玻璃在700 ℃的条件下经H₂还原,得到具有奇特光致发光性质的Ge/SiO₂玻璃,该玻璃在室温条件下用246 nm（5.01 eV）的光激发时,能发射出很强的 392 nm（3.12 eV）、较强的 600 nm（2.05 eV）和次强的770 nm（1.60 eV） 的荧光.利用X射线衍射（XRD）、X射线光电子能谱（XPS）及透射电镜（TEM）实验证明,该玻璃能够发射3种不 关键词： 2')" href="#">Ge/SiO₂ Ge纳米晶粒 溶胶/凝胶法 光致发光     

纳米TiO2多孔膜的微结构对染料敏化纳米薄膜太阳电池性能的影响

采用溶胶-凝胶方法，在不同的实验条件下获得平均粒径从15到25nm左右的纳米TiO２2颗粒.利用这些颗粒制备出的纳米多孔薄膜，应用于染料敏化纳米薄膜太阳电池. 通过x射线 衍射仪分析，得到TiO２₂颗粒的晶相以及晶粒度大小，用透射电子显微镜观察 了纳米TiO２₂颗粒的形貌和尺寸.应用于太阳电池的纳米TiO２₂多 孔膜，经基于布朗诺尔-埃米特-泰 勒（BET）的多层吸附理论的比表面积测试和孔径分布测试，获得了多孔膜的微 关键词： 溶胶-凝胶法 2')" href="#">纳米TiO２₂ 染料敏化 太阳电池     

溶胶-凝胶法制备的Ba0.8Sr0.2TiO3薄膜的结构及铁电性质研究

采用0.05mol/L的前驱体溶液,利用溶胶-凝胶法成功制备了室温下具有优良铁电性质的Ba_0.8Sr_0.2TiO₃ (BST)薄膜.X射线衍射分析表明,制得的BST薄膜室温下呈四方相,场发射扫描电子显微观测显示BST薄膜表面平整、致密、无裂纹出现,薄膜晶粒呈柱状结构、尺寸在150nm左右.电学测量表明制备的BST薄膜室温下具有优良的铁电性能.薄膜的剩余极化P_r约为35μC/cm²,矫顽电场E关键词：     

前驱溶液的pH值对制备Ca2Zn4Ti16O38 ∶ Pr3+,Na+ 发光粉物相、形貌和发光性质的影响

以钛酸丁酯、醋酸钙、醋酸锌、柠檬酸和乙二醇为原料,采用溶胶-凝胶法制备Ca₂Zn₄Ti₁₆O₃₈ ∶ Pr³⁺, Na⁺ 发光粉。研究了前驱溶液的pH值对溶胶-凝胶转变过程、发光粉物相组成、样品形貌和发光性质的影响。通过热重-差热分析(TG/DTA)、X射线衍射(XRD)分析、扫描电子显微镜(SEM)对前驱物分解、发光粉物相和颗粒大小进行了研究。采用荧光光谱对材料的光谱性质进行了表征。研究发现前驱溶液pH ≤ 3时,所得发光粉样品为蓬松的、颗粒均匀的单相Ca₂Zn₄Ti₁₆O₃₈粉末,红色余辉时间较长;随着pH值增大,逐渐有杂质相TiO₂、CaTiO₃和Zn₂TiO₄生成,并且样品颗粒逐渐变大,颗粒团聚呈现不规则形状,余辉时间变短。结果表明,只有在pH ≤ 3条件下以溶胶-凝胶法制备Ca₂Zn₄Ti₁₆O₃₈ ∶ Pr³⁺, Na⁺ 发光粉下才能获得被日光有效激发,并呈现余辉衰减慢的红色长余辉(644 nm)发光。     

Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method

Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.     

Synthesis and structural determination of the new oxide fluoride BaFeO2F

Low temperature fluorination of BaFeO_3−x using poly(vinylidene fluoride) leads to the formation of the oxide fluoride BaFeO₂F. Mössbauer spectroscopy shows that this phase exhibits magnetic ordering at room temperature due to interactions between the Fe³⁺ ions, with an ordering temperature of 645 (±5) K. Neutron diffraction studies show that the phase has cubic symmetry and confirm the presence of magnetic ordering (G-type antiferromagnetic) at room temperature.     

Synthesis and optimum luminescence of monodispersed spheres for BaWO4-based green phosphors with doping of Tb

Monodispersed spheres for Tb³⁺-doped BaWO₄ (BWO:Tb) phosphors were prepared by a hydrothermal method. X-ray diffraction (XRD) and field-emission scanning electron microscopy were used to characterize the resulting samples. Emission and excitation spectra were studied using xenon excited spectroscopic experiments at room temperature. Because 12 at% BWO:Tb phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), it is considered to be a new promising green phosphor for fluorescent lamps application.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

Synthesis and luminescent properties of nanoparticles GdCaAl3O7:RE (RE=Eu, Tb) via the sol-gel method

By using metal nitrates as starting materials and citric acid as complexing agent, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ powder phosphors were prepared by a citrate-gel method. Thermal analysis (TG-DTG), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results of the XRD indicated the precursor samples began to crystallize at 800 °C and the crystallinity increased with elevation the annealing temperature. TEM images showed that the phosphor particles were basically of spherical shape, with good dispersion about a particle size of around 40-70 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺, and at around 543 nm corresponding to the ⁵D₄-⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺ (or Tb³⁺) concentration and annealing temperature were also studied in detail.     

电子束辐照诱导Bi:α-BaB2O4 单晶近红外宽带发光的研究

用提拉法技术生长出了Bi:α-BaB₂O₄单晶,并进行电子束辐照.测定了电子束辐照前后的吸收谱和荧光发射谱.在808 nm波长激光二极管的激发下,电子束辐照后的Bi:α-BaB₂O₄单晶中观测到了中心波长在1135 nm附近、半高宽为52 nm左右的近红外宽带发光现象.近红外宽带发光的发光中心是Bi⁺离子.电子束射线起到了将Bi³⁺和Bi²⁺还原至一价态 关键词： 近红外宽带发光 2O₄单晶')" href="#">α-BaB₂O₄单晶 电子束辐照     

Preparation, structure and ferromagnetic properties of the nanocrystalline Ti1-xMnxO2 thin films grown by radio frequency magnetron co-sputtering

This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.     

Sol-gel growth of Gd2MoO6:Eu nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6:Eu) and their luminescent properties

SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO₂@Gd₂MoO₆:Eu³⁺ core-shell phosphors. The XRD results demonstrate that the Gd₂MoO₆:Eu³⁺ layers on the SiO₂ spheres begin to crystallize after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd₂MoO₆:Eu³⁺ shells on the SiO₂ cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu³⁺ shows a strong PL luminescence (dominated by ⁵D₀-⁷F₂ red emission at 613 nm) under the excitation of 307 nm UV light. The PL intensity of Eu³⁺ increases with increasing the annealing temperature and the number of coating cycles.     

Mössbauer spectroscopic studies of the disintegration of hexavalent iron compounds (BaFeO4 and K2FeO4)

Mössbauer spectroscopic studies of BaFeO₄ and K₂FeO₄ as prepared, then either sealed, or exposed to air, or exposed to moist air for a period up to more than one year, were performed at room temperature as a function of time. Some of the samples were studied as a function of temperature down to 4.2 K. K₂FeO₄ and BaFeO₄ after preparation, exhibit a pure Fe⁶⁺ spectrum. K₂FeO₄ shows low stability. After a period of 14 months in a sealed sample holder, the spectrum exhibits 83% noncrystalline Fe³⁺, as Fe₂O₃ nanoparticles, and only 17% of the original Fe⁶⁺. BaFeO₄ sealed, or exposed to dry air disintegrates slowly, exhibiting a spectrum composed of three subspectra. In addition to the original Fe⁶⁺ and final Fe³⁺ subspectra, a subspectrum, of an intermediate stage of a crystalline Fe⁴⁺ system, is present. In the first month the increase of the Fe³⁺ subspectrum is 15%, and that of the Fe⁴⁺ is 8%. BaFeO₄ exposed to moist air, disintegrates at a very fast rate. The Fe³⁺ subspectrum, due to Fe₂O₃ nanoparticles, increases in the first days at the rapid rate of ∼13%/day, and there is no evidence for Fe⁴⁺ in the spectrum. The Fe⁶⁺ in BaFeO₄, Fe³⁺ and Fe⁴⁺ in the disintegrated systems are all magnetically ordered at 4.2 K. Above 90 K the Fe³⁺ subspectra exhibit a superposition of a paramagnetic doublet and a diffuse magnetic sextet, with relative intensities changing with temperature, and changing from sample to sample according to their blocking temperatures, which are determined by the distribution in size of the nanoparticles.