溶胶-凝胶法Er_2O_3薄膜的结构和光学特性

针对稀土Er掺杂Si光源中Er离子掺杂浓度低的问题,采用溶胶-凝胶(Sol-gel)法在Si(100)和SiO2/Si(100)基片上旋涂法制备Er2O3光学薄膜,Er离子浓度与以前掺杂方法相比提高了2个数量级.900℃热处理获得单一立方结构的Er2O3薄膜材料.光致发光(PL)特性研究表明在654nm波长的激光泵浦下,Er2O3薄膜材料获得了1.535μm的发光峰,并具有较小的温度猝灭1/5.在SiO2/Si(100)基体上制备的Er2O3薄膜材料的光致发光强度比Si(100)基体上制备的薄膜提高2-3倍.研究结果表明具有强光致发光特性的Er2O3薄膜是一种有前景的硅基光源和放大器材料.     

铁掺杂多孔氧化铟的NO2传感特性

研究NO2传感器材料特性和工作机理,对监测大气污染及人体健康保护有重要意义.本文采用水热法合成了铁掺杂的多孔In2O3纳米颗粒,并基于上述纳米颗粒制备了NO2传感器.运用X射线衍射仪、扫描电子显微镜、透射电子显微镜和比表面积测试对所制备的纳米颗粒进行微观形貌表征,同时对传感器性能包括温度特性、响应-恢复特性、选择性和稳定性等进行研究.研究发现,当In和Fe摩尔比为9∶1时,由铁掺杂多孔In2O3纳米颗粒制作的传感器对NO2气体具有优秀的选择性和较短的响应-恢复时间.在260℃的工作温度下,传感器对浓度为50 ppm (1 ppm=1 mg/L)的NO2气体的灵敏度值为960.5,响应时间和恢复时间分别为5和6 s.形貌测试结果表明,采用Span-40做活性剂制备的铁掺杂In2O3纳米颗粒为边长50—200 nm的方形结构,其中分布大量细小孔洞,这是导致大的比表面积和高灵敏度的主要原因之一.同时,从空间电荷、内建势垒和掺杂前后能带变化等理论出发,对所制备传感器的传感机理进行了分析.     

纳米晶La2O3的制备及其红外吸收特性的研究

采用硬脂酸凝胶法制备了La2O3纳米晶,用X射线粉末衍射仪(XRD),透射电子显微镜(TEM)对La2O3纳米晶的粒径和形貌进行了表征.研究了不同热处理温度下纳米La2O3的红外吸收特性,结果表明,La2O3纳米晶的吸收峰的宽化、吸收峰发生蓝移和红移现象,同时La2O3纳米晶在1 000～1700 nm之间吸收较好,有可能用作激光隐身涂料的吸收剂.     

高取向度的毫米波锶钙六角多晶铁氧体

采用普通陶瓷工艺,进行湿压磁场成型和氧气氛烧结,同时加入微量杂质(Bi2O3和MnCO3),制备了各向异性多晶六角铁氧体材料Sr095Ca005Fe12O19.结果表明:该六角铁氧体的取向度达100%,介电损耗为23×10-3,具有非常良好的磁特性.对其比饱和磁化强度(σs)、磁晶各向异性场(Ha)与温度(T)的变化关系进行了研究,并与SrFe12O19六角铁氧体的磁特性进行了比较 关键词： 取向度 介电损耗 比饱和磁化强度 磁晶各向异性     

添加Ag_2O对YBa_2Cu_3O_(7-δ)体材料显微结构与超导电性的影响 (Ⅰ)制备工艺与超导电性

本文比较系统地研究了添加 Ag_2O 对 YBa_2Cu_3O_(7-δ)体材料超导电性的影响.结果表明:在制备过程中添加适量 Ag_2O 可以显著增强 YBa_2Cu_3O_(7-δ)晶粒间的耦合,并改善 YBa_2Cu_3·O_(7-δ)体材料的超导性能.对于在930—1000℃范围内烧成,名义组成为(YBa_2Cu_3O_(7-δ))_(1-x)Ag_x(x=0.2～0.55)的复合超导试样来说,烧成温度对试样的超导性能起关键的作用,而 Ag_2O的添加量(x)和预烧温度的作用相对要小得多,当烧成温度高于970℃时 Ag_2O 的添加效果极为明显.例如1000℃烧成的 x=0.3的试样在77K 下的磁化临界电流密度 J_c 比相同工艺条件制备的未加 Ag_2O 试样提高五倍多.     

高温高压方法合成碳包覆γ-Fe_2O_3纳米棒及其磁学性能

采用高温高压(HPHT)方法,以水热法制备的聚乙烯醇包覆FeOOH纳米棒为前驱体,合成了碳包覆γ-Fe2O3纳米棒.通过使用多种表征方法,研究了HPHT过程中合成温度对样品结构和形貌的影响,并对样品的生长机理进行了探讨.利用振动样品磁强计测量了样品的室温磁学性质.实验结果表明,反应温度为400?C,压强为1 GPa条件下制备的碳包覆γ-Fe2O3纳米棒具有较高的长径比(直径约为20 nm,长度约为150 nm),矫顽力可达到330 Oe(1 Oe=79.5775 A/m).该方法为制备具有核壳结构的一维纳米材料提供了新思路.     

MBiO2Cl(M=Ca,Sr,Ba)材料的合成、能带计算及发光性能研究

采用固相合成方法制备出CaBiO2Cl,SrBiO2Cl和BaBiO2Cl粉体,研究了该Sillen系列铋基氧卤化合物的光学带隙、电子结构及发光性能.基于密度泛函理论计算表明,SrBiO2Cl和BaBiO2Cl均为直接带隙半导体材料,与吸收光谱实验结果相符合.在X射线和紫外光激发下三者均具有宽的可见光发射带(400-550 nm),尤其是BaBiO2Cl粉体的光输出强度约为Bi4Ge3O12(BGO)粉体光输出强度的1.4倍,并且具有更短的衰减时间,发光衰减时间的主要部分为100 ns(22%)和300 ns(41%),而BGO粉体的主要衰减时间为300 ns(75%).实验分析表明,该化合物发光性能与晶体结构中Bi-O(Cl)键长及碱土金属离子的半径相关.同时BaBiO2Cl具有较大的密度(6.98 g/cm3,因此它是一种具有潜在应用价值的闪烁材料.     

直流反应溅射法制备Y_2O_3隔离层的研究

采用直流反应溅射的方法在具有立方织构的Ni基底上制备出了Y2O3隔离层,并研究了基带温度与H2O分压两个因素对Y2O3薄膜的织构取向以及表面形貌的影响。X射线衍射(XRD)结果和扫描电子显微镜(SEM)的分析表明,在温度为760℃,H2O分压为1.68×10-2Pa的条件下制备出的Y2O3薄膜具有强立方织构,平面内Φ扫描半高宽为7.07°,其表面均匀、致密、无裂纹。     

退火温度对YBa2Fe3O8的结构与磁性质影响分析

YBa2Fe3O8(YBFO)是具有三方钙钛矿结构的反铁磁(AFM)体,研究它的结构和磁性质对于我们认识三方钙钛矿结构具有重要作用.目前,关于固相法制备YBFO中退火温度方面的研究并不多,而控制退火温度是这种工艺中的重要环节.为制备高含量的YBa2Fe3O8,本文分别在760℃、950℃和1100℃退火温度下,采用固相...     

原子层沉积制备Al_2O_3薄膜的光学性能研究

研究了原子层沉积制备氧化铝薄膜的光学性能。以三甲基铝(TMA)和水为前聚体,分别在基板温度为250℃和300℃的K9和石英玻璃衬底上沉积了Al2O3光学薄膜。采用分光光度计,X射线光电子能谱(XPS),X射线衍射(XRD),原子力显微镜(AFM),扫描电子显微镜(SEM)等分析手段对薄膜的微结构、表面形貌和光学特性进行了研究。结果表明,原子层沉积法制备的Al2O3薄膜在退火前后均呈现无定形结构,元素成分接近化学计量比,其表面粗糙度小于1.2nm,聚集密度高于0.97,光学非均匀性优于1%。同时在中紫外到近红外均有很好的光学性能,适合作为中间折射率和低折射率材料在光学薄膜中得到应用。     

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH₃)₄ groups.     

Study of superstructure II in multiferroic BiMnO3

The crystal structure of the minor phase, named superstructure II, existing in multiferroic compound BiMnO3 has been studied by electron diffraction and high-resolution transmission electron microscopy. Domains of major and minor phases coexisting in BiMnO3 were observed in high-resolution electron microscope images. The unit cell of minor phase was determined to be triclinic with the size 4×4×4 times as large as the distorted perovskite subcell. The [111] and [101] projected structure maps of the minor phase have been derived from the corresponding images by means of the image processing. A possible rough three-dimensional （3D） structure model was proposed based on the 3D structural information extracted from the two projected structure maps. Since there is no inversion centre in the proposed model, the minor phase may contribute to the ferroelectric property of BiMnO3.     

The first-principle studies of the crystal phase transitions: Fd3m-MgAl2O4→F4-3m-MgAl2O4

Magnesium aluminum spinel (MgAl₂O₄) is a major constituent of the shallow upper mantle. It is of great geophysical importance to explore its physical properties under high pressure and temperature. The first-principle density functional theory (DFT) with the plane wave along with pseudopotential was employed to obtain the total energy for both Fd3m-MgAl₂O₄ and F4-3m-MgAl₂O₄, which was used to generate the Gibbs free energy as a function of temperature and pressure with the quasi-harmonic Debye model. It is found that the phase transition temperature from Fd3m-MgAl₂O₄ to F4-3m-MgAl₂O₄ is beyond 452.6 K in the pressure regime studied, which is consistent with the experiment. The phase transition temperature is related to pressure by a linear function, i.e. T=8.05P+452.6, which is the first equation of this kind to describe the phase transition Fd3m→F4-3m. The elastic constants, equation of states and thermodynamic properties of Fd3m-MgAl₂O₄ are also reported in this paper to make a complete study.     

First principles studies of elastic and thermodynamic properties of fcc-VH2 with pressure and temperature

In this work, we study elastic and thermodynamic properties of VH₂ at different pressures and temperatures. Elastic constants and bulk modulus of VH₂ decrease with increase in temperature, and hence increase with pressure. Thermal expansion of the crystal lattice will be suppressed by high pressure. When the temperature is 1500 K, 15.99 GPa of pressure can completely restrain the volume expansion caused by temperature. At a given pressure, the lower the temperature, the easier the cell compression. At low temperatures, C_v is proportional to T³, and C_v tends to the Dulong-Petit limit at higher temperatures. The Debye temperature increases with pressure, but decreases with temperature. At low temperature and low pressure, thermal expansion coefficient increases sharply with temperature. At high temperature and high pressure, the increasing trend slows down.     

Magnetic ground state and multiferroicity in BiMnO<Subscript>3</Subscript>

We argue that the centrosymmetric C2/c symmetry in BiMnO₃ is spontaneously broken by antiferromagnetic (AFM) interactions existing in the system. The true symmetry is expected to be Cc, which is compatible with the noncollinear magnetic ground state, where the ferromagnetic order along one crystallographic axis coexists with the hidden AFM order and related to it ferroelectric polarization along two other axes. The C2/c symmetry can be restored by the magnetic field B ∼ 35 T, which switches off the ferroelectric polarization. Our analysis is based on the solution of the low-energy model constructed for the 3d-bands of BiMnO₃, where all the parameters have been derived from the first-principles calculations. Test calculations for isostructural BiCrO₃ reveal an excellent agreement with experimental data. The article is published in the original.     

Elastic and thermodynamic properties of CaB6 under pressure from first principles

The elastic and thermodynamic properties of CsCl-type structure CaB₆ under high pressure are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaB₆ under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. The pressure dependences of the elastic constants, bulk modulus B (GPa), and its pressure derivative B′, shear modulus G, Young's modulus E, elastic Debye temperature Θ_B, Zener's anisotropy parameter A, Poisson ratios σ, and Kleinmann parameter ζ are also presented. An analysis for the calculated elastic constants has been made to reveal the mechanical stability of CaB₆ up to 100 GPa. The thermodynamic properties of the CsCl-type structure CaB₆ are predicted using the quasi-harmonic Debye model. The pressure-volume-temperature (P-V-T) relationship, the variations of the heat capacity C_V, Debye temperature Θ_D, and the thermal expansion α with pressure P and temperature T, as well as the Grüneisen parameters γ are obtained systematically in the ranges of 0-100 GPa and 0-2000 K.     

钙钛矿型氧离子导体KNb1-xMgxO3-δ的制备和表征

在高温高压（4.0GPa，870℃）下合成了具有正交钙钛矿结构的KNb_1-xMg_x O_3-δ（x=0.0—0.3）系列固体电解质，并系统地研究了Mg掺杂对其结构相变和导电性的影响.变温拉曼谱和DTA测量结果表明，随着温度的升高，KNb_{1-xMgxO3-δ发生了结构相变，由铁电正交、四方相转变为顺 电立方相.由于Mg掺杂削弱了B位离子对自发极化的贡献以及A位离子与BO关键词： 钙钛矿 离子电导 1-xMgxO3-δ')" href="#">KNb1-xMgxO3-δ 高温高压 铁电相变}     

Coupling between Ge-nanocrystals and defects in SiO2

Room temperature photoluminescence (PL) at around 600 nm from magnetron-sputtered SiO₂ films co-doped with Ge is reported. The PL signal is observed in pure SiO₂, however, its intensity increases significantly in the presence of Ge-nanocrystals (Ge-nc). The PL intensity has been optimized by varying the temperature of heat treatment, type of gas during heat treatment, concentration of Ge in the SiO₂ films, and gas pressure during deposition. Maximum intensity occurs when Ge-nc of around 3.5 nm are present in large concentration in SiO₂ layers deposited at fairly high gas pressure. Based on time resolved PL, and PL measurements after α-particle irradiation or H passivation, we attribute the origin of the PL to a defect in SiO₂ (probably an O deficiency) that is excited through an energy transfer from Ge-nc. There is no direct PL from the Ge-nc; however, there is a strong coupling between excitons created in the Ge-nc and the SiO₂ defect.     

Experimental and kinetic modeling study of C2H4 oxidation at high pressure

A detailed chemical kinetic model for oxidation of C₂H₄ in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C₂H₃ + O₂ reaction was used to obtain rate coefficients over a wide range of conditions (0.003-100 bar, 200-3000 K). The results indicate that at 60 bar and medium temperatures vinyl peroxide, rather than CH₂O and HCO, is the dominant product. The experiments, involving C₂H₄/O₂ mixtures diluted in N₂, were carried out in a high pressure flow reactor at 600-900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C₂H₄ are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH₂CH₂OH) and 2-hydroperoxyethyl (CH₂CH₂OOH) radicals, formed from addition of OH and HO₂ to C₂H₄, and vinyl peroxide, formed from C₂H₃ + O₂. Hydroxyethyl is oxidized through the peroxide HOCH₂CH₂OO (lean conditions) or through ethenol (low O₂ concentration), while 2-hydroperoxyethyl is converted through oxirane.