外延压应变对BaTiO$lt;sub$gt;3$lt;/sub$gt;铁电体抗辐射性能影响的分子动力学研究

采用基于壳模型的分子动力学模拟方法, 研究了存在外延压应变时BaTiO₃铁电体的辐射位移效应, 以O原子作为初冲原子(primary knock-on atom, PKA), 能量为1 keV, 方向为[001], 分别计算了外延压应变为0, 0.4%, 0.8%, 1.2%, 1.6%, 2.0%时体系的缺陷数量、分布, 以及辐射前后的极化强度, 比较了压应变为2%以及无应变下损伤区域、缺陷离位距离和反向外电场下PKA的迁移距离. 结果表明, 随外延压应变增加体系极化近似线性增加, 辐射后极化降低幅度降低、缺陷产生的数量有所减小, 2% 压应变存在时缺陷原子的离位距离、PKA在反向外电场作用下的迁移距离和损伤区域都小于无应变的情况, 说明外延压应变的存在对辐射造成的晶格损伤具有抑制作用, 对辐射损伤具有改善作用, 可以通过引入外延压应变来调控BaTiO₃的辐射损伤. 关键词： 应变 3')" href="#">BaTiO₃ 辐射损伤 分子动力学模拟     

Ba10(PO4)4(SiO4)2∶Eu2+荧光体的光谱特性

采用高温固相法合成了荧光体Ba₁₀（PO₄）₄（SiO₄）₂：Ce³⁺和Ba₁₀（PO₄）₄（SiO₄）₂：Eu²⁺,研究了两种荧光体的光谱特性。结果表明,两者都呈现较强的宽带激发特征。根据同种基质中Eu²⁺和Ce³⁺两种离子光谱特征的相关性,通过测得的Ba₁₀（PO₄）₂（SiO₄）₂基质中Ce³⁺的光谱数据估算了Ba₁₀（PO₄）₂（SiO₄）₂：Eu²⁺中Eu²⁺的斯托克斯位移（ΔS）和激发能量,估算结果与Ba₁₀（PO₄）₂（SiO₄）₂：Eu²⁺样品的光谱分析结果十分吻合。Ba₁₀（PO₄）₂（SiO₄）₂：Eu²⁺可以同时被紫光和蓝光激发,发出偏白的绿光,可用作白光LED的荧光粉。     

Formation of Ca-doped YBa2Cu4O8 phase in thin films

Ca-doped YBa₂Cu₄O₈ (124) thin films are prepared on (100) SrTiO₃ substrates by annealing the amorphous films deposited using a pulsed laser deposition technique. The X-ray diffraction measurements show that the Ca-doped YBa₂Cu₄O₈ phase is formed by annealing below 800°C at a oxygen pressure of 1 atm. The 124 films have c-axis orientation normal to the substrates. As the Ca content increases, the proportion of the 123 impurity phase in the samples increases. The onset temperature of superconductivity of the Y(Ca)Ba₂Cu₄O₈ films increases from 79 K to 88 K with an increase Ca-substitution for 5 to 10% of Y.     

Ba5(PO4)3Cl：Eu2+荧光粉的制备和发光性能研究

以Eu₂O₃、NH₄H₂PO₄、BaCl₂·2H₂O、BaCO₃为原料,用高温固相法制备出Ba₅（PO₄）₃Cl：Eu²⁺荧光粉。用XRD衍射仪和荧光分光光度计分别测试样品的物相结构和荧光性能。结果表明：制备得到的Ba₅（PO₄）₃Cl：Eu²⁺为单相,在245~425 nm范围均有较大吸收,具有最强峰在435 nm的窄带发射。该荧光粉的发光强度受Eu²⁺浓度的影响较大,其发光随着Eu²⁺浓度的增加先增强后减弱。当Eu²⁺摩尔分数为3%时,发光强度达到最大。     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

强自旋轨道耦合化合物Sr2-xLaxIrO4的掺杂和拉曼谱学

利用固相反应法成功制备了Sr_2-xLa_xIrO₄系列掺杂样品, 并详细研究了样品晶体结构随掺杂的演变. 拉曼散射峰向高频移动和X射线衍射谱的结构精修数据发现随着掺杂量的增加, c轴晶格常数减小, 顶角Ir–O1键键长随之减小, 表明掺杂导致晶格收缩, 而且IrO₆八面体畸变程度减弱. 变温拉曼散射谱显示随着温度降低也出现蓝移现象, 且与顶角氧相关的拉曼振动模式的蓝移在110 K附近出现明显跳变, 表明在该温度附近出现了结构变化和磁性质转变.     

应变对钴铁氧体电子结构和磁性能影响的第一性原理研究

尖晶石型钴铁氧体(CoFe₂O₄)因具有良好的电磁性质, 广泛应用于计算机技术、航空航天及医学生物等领域. 特别是钴铁氧体薄膜在磁电复合材料中具有良好的应用前景. 本文基于密度泛函理论的第一性原理平面波赝势法, 结合广义梯度近似, 通过采用更接近于实验上外延生长的二维应变模型, 研究了钴铁氧体薄膜的结构稳定性、电子结构和磁性能. 结果表明: 在二维应变作用下, 反尖晶石结构的钴铁氧体比正尖晶石结构的稳定, 但是与平衡基态相比, 两者能量差减小, 这表明在应变作用下, 八面体晶格中的Co²⁺离子与四面体晶格中的Fe³⁺离子更容易进行位置交换, 形成混合型结构的钴铁氧体; 同时随着应变的增大, 钴铁氧体的能带带隙减小, 晶格中的原子磁矩发生变化, 但总磁矩变化不明显. 关键词： 尖晶石型钴铁氧体 第一性原理 电子结构 磁性能     

Ba2SiO4:Ce3+,Mn2+荧光粉的制备与光谱性质

用高温固相反应法合成了Ba₂SiO₄:xCe³⁺,yMn²⁺(x=0~0.2, y=0~0.15)荧光粉,研究了荧光粉的晶体结构和发光性质。在紫外光激发下,Ba₂SiO₄:xCe³⁺的发射光谱为位于384 nm附近的宽带。Ba₂SiO₄:Mn²⁺样品的发射光谱位于376 nm的宽带较强,红光发射极弱。在Ce³⁺和Mn²⁺共掺的Ba₂SiO₄:xCe³⁺,yMn²⁺样品中,位于606 nm附近的红光发射较强,来源于Mn²⁺的⁴T₁(⁴G)-⁶A₁(⁶S)跃迁。这说明Ce³⁺离子将部分能量传递给了Mn²⁺离子,有效地敏化了Mn²⁺离子的发光。当Ce³⁺的摩尔分数为0.2、Mn²⁺的摩尔分数为0.075时,Ba₂SiO₄:xCe³⁺,yMn²⁺荧光粉位于606 nm的Mn²⁺的发射峰最强。     

新型Ba3SiO5:Eu荧光粉的合成及光谱性质

以BaCO_3、SiO_2、Eu_2O_3为原料在还原气氛下采用高温固相法制备了Ba_3SiO_5∶Eu荧光粉体。实验结果表明,制备Ba_3SiO_5的最佳工艺条件是Ba/Si比为3,1 200℃保温4 h。光谱分析表明,Ba_3SiO_5∶Eu荧光粉在254,365,410 nm激发下发射主峰为566 nm(Eu~(2+)的4f~n~(-1)5d→4f~n)宽带发射,量子效率分别为70%、50%、10%,荧光寿命为百纳秒级;以566 nm为监视波长测得激发谱为主峰在250～450 nm范围内的宽带发射,主峰为360 nm,且在410 nm出现小峰; Eu离子最佳掺杂浓度为5%,由发光强度随掺杂离子浓度变化曲线,可以得出Ba_3SiO_5中Eu离子能量传递是基于电四级-电四级作用。     

Ba5SiO4Cl6: Yb3+, Er3+, Li+荧光粉的制备及上转换发光性质研究

本文采用高温固相反应法制备了Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺, Li⁺ 荧光粉, 并对其上转换发光性质及其发光机理进行了研究. 在980 nm 激光的激发下, Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺ 荧光粉呈现较强的红色(662 nm) 和较弱的绿色(550 nm) 的上转换发光, 红色和绿色的上转换发光分别对应于Er³⁺ 离子的⁴S_3/2/²H_11/2→⁴I_15/2 和⁴F_9/2→⁴I_15/2 跃迁, 且随着掺杂的Er³⁺ 和Yb³⁺ 离子浓度增加, 样品的上转换发光强度增加, 这是因为Yb³⁺ 离子和Er³⁺ 离子之间的能量传递效率增加引起的. 在0.5—0.8 W 功率激发下,样品属于双光子发射, 而在0.9—1.2 W 功率激发下样品具有新的上转换发光机理——光子雪崩效应. 探讨了Li⁺ 掺杂对Ba₅SiO₄Cl₆: Yb³⁺, Er³⁺ 样品的上转换发光性质的影响, Li⁺ 离子的掺杂引起Ba₅SiO₄Cl₆:Yb³⁺, Er³⁺ 上转换发光强度增加, 这是由于Li⁺ 离子的掺入降低了晶体场的对称性引起的.     

High critical current density YBa2Cu3O7−δ tapes prepared by the surface-oxidation epitaxy method

YBa₂Cu₃O_7−δ (YBCO) films with high critical current density (J_c) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature (T_c) of 87 K and J_c=4–6×10⁴ A/cm² (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO₂, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of T_c=88 K and J_c=3×10⁵ A/cm² (77 K, 0 T) and 1×10⁴ A/cm² (77 K, Hc, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high-J_c values.     

High pyroelectric Ba0.65Sr0.35TiO3 thin films with Ba0.65Sr0.35RuO3 seeding-layer for monolithic ferroelectric bolometer

Ba_0.65Sr_0.35TiO₃ (BST) thin films were deposited by RF sputtering with a very thin Ba_0.65Sr_0.35RuO₃ (BSR) seeding-layer on Pt/Ti/SiO₂/Si substrate. The crystallization of BST thin films and the surface morphology of BSR seeding-layer were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD patterns show that the BSR seeding-layer affected the orientation of BST thin film, which is highly a-axis textured. It was also found that the BSR seeding-layer had a marked influence on the dielectric properties of BST thin films. Comparing with BST thin films directly deposited on Pt electrode, the dielectric relaxation can be suppressed and dielectric constant increased due to a possible reduction of interface oxygen vacancies at BST/BSR interface. Moreover, J–V measurement indicates that the leakage current density of BST thin films on BSR seeding-layer were greatly reduced compared with that of BST thin films directly on Pt electrodes. The pyroelectric coefficient of BST thin films with BSR seeding-layer is 7.57 × 10⁻⁷ C cm⁻² K⁻¹ at 6 V/μm at room temperature (RT). Our results reveal that high pyroelectric property of BST thin film could be achievable using BSR seeding-layer as a special buffer.     

SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

High quality epitaxial YBa₂Cu₃O_7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO₃, LaAlO₃ and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a J_c (at 77 K, H=0) over 10⁶A/cm². It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa₂Cu₃O_7-x films had excellent superconducting properties and quite perfect structure.     

Ho3+掺杂的Ba0.8Sr0.2TiO3厚膜的发光特性

用丝网印刷法在氧化铝衬底上制备了Ho3+掺杂的Ba0.8Sr0.2TiO3(BST)厚膜.XRD谱表明,随着Ho3+掺杂摩尔分数从0.5%增加到2.0%,BST厚膜的晶格尺寸先增大后减小.在514 nm的氩离子激光激发下,样品均出现了中心波长为549,650,753 nm的发光带,分别对应于Ho3+离子的(5F4,5S...     

近紫外光激发黄色荧光粉Ba3Y4O9：Dy3+的制备及发光特性

通过高温固相法合成了一系列Ba₃Y_4-xO₉：xDy³⁺荧光粉材料。利用X射线粉末衍射、荧光光谱和荧光寿命对样品进行了表征。实验表明,样品的激发光谱由一系列线状峰组成,峰值分别位于328,355,368,386,427,456,471 nm。在355 nm激发下,荧光粉在490 nm（⁴F_9/2→⁶H_15/2）和580 nm（⁴F_9/2→⁶H_13/2）处有很强的发射,发射光谱的色坐标位于黄光区域。研究了不同Dy³⁺掺杂浓度对样品发光性质的影响,发现样品的发光随着Dy³⁺浓度的增大而增强,但光谱形状基本保持不变,表明Dy³⁺占据了基质中低对称性的Y³⁺格位。当Dy³⁺摩尔分数x=0.08时出现发光强度猝灭现象,浓度猝灭机理为电偶极-电偶极相互作用。样品的发光寿命随着Dy³⁺浓度的增大逐渐减小,进一步证明了Dy³⁺离子之间存在着能量传递现象。Ba₃Y₄O₉：Dy³⁺荧光粉的发光位于黄光区域,有较好的热稳定性,是潜在的白光LED用荧光粉材料。     

Direct observation of flux-creep in high-Tc superconductors using the high-resolution Faraday effect

Using the capability of the high-resolution Faraday effect (HRF) to allow dynamic observations of the Shubnikov phase, we directly observed effects of flux-creep in high -T_c superconductors. In this paper we show measurements on (RE) Ba₂Cu₃O_7-δ with RE=Y, Dy, Gd and on Bi₂Sr₂CaCu₂O_8−δ single crystals and also on YBaCuO thin films and sintered materials. Furthermore, this technique enables us also to measure the flux creep locally. From the obtained photographs we determine the time dependence of the total flux in the samples. Using these data and the model of Hagen et al. the effective activation energies have been determined for these materials.     

Ferromagnetic resonance study of interface anisotropies in exchange-biased Fe(0 0 1)/KNiF3 bilayers

Magnetic anisotropies at epitaxial Fe/KNiF₃ interfaces were probed by ferromagnetic resonance. Fe(0 0 1) films coupled to single crystal KNiF₃ exhibit four-fold in-plane anisotropy and a unidirectional bias upon field-cooling. In Fe(0 0 1) with polycrystalline KNiF₃, the bias direction deviates from the field-cooling direction. Lattice mismatch strain due to polycrystalline KNiF₃ also induces uniaxial anisotropy in Fe.     

Li+和Er3+掺杂对Ba2SiO4：Eu2+发光性能的影响

采用化学沉淀法一次煅烧工艺制备了Ba_1.99-x/2-2ySiO₄:Eu_0.01²⁺, Li_x+y²⁺, Eu_y³⁺绿色荧光粉, 用X射线衍射仪和荧光分光光度计对样品的晶体结构、发光性能进行表征. 结果表明: 少量Eu²⁺, Li⁺和Er³⁺的共掺杂没有改变晶体结构; 其激发光谱分布在270–440 nm波长范围, 谱峰位于288 nm, 360 nm处, 可以被InGaN 管芯产生的360–410 nm辐射有效激发; 在360 nm近紫外光激发下, 测得其发射光谱峰值在500 nm 处, 是Eu²⁺4f⁶5d¹→4f⁷跃迁的典型发射; 荧光粉发光强度随着Li⁺掺杂量的增大先增强, 后减弱, 当x=0.1时, 发光强度最大; 随着Li⁺, Er³⁺共掺杂量的增加(y=0.012), 出现位于530 nm和488 nm的发射峰, 对应于Er³⁺的²H_11/2→⁴I_15/2和⁴F_7/2→⁴I_15/2特征发射, 同时分析了Eu²⁺→Er³⁺的能量传递过程. 关键词： 化学沉淀法 2SiO₄：Eu²⁺,Li⁺,Er³⁺')" href="#">Ba₂SiO₄：Eu²⁺,Li⁺,Er³⁺ 能量传递 发光性能     

应力作用下EuTiO3铁电薄膜电热效应的唯象理论研究

基于Laudau-Devonshire的热动力学模型, 计算了EuTiO₃铁电薄膜材料的电热效应. 结果显示在外加应力的调控下, 电极化、电热系数以及绝热温差都会随之变化. 外加垂直于表面的张应力加大, 薄膜的相变温度升高, 绝热温差增加, 最大绝热温差所对应的工作温度向高温区移动. 对于二维平面失配应变u_m =-0.005的薄膜, 当外加张应力σ₃ = 5 GPa时, 其最大电热系数为1.75×10^-3 C/m²·K, 电场变化200 MV/m 时室温下绝热温差ΔT 的最大值可达到14 K 以上, 绝热温差ΔT ≥13 K 的工作温区超过120 K, 表明可以通过调控外部应力来获取室温时较大的绝热温差. 此结果预示着铁电EuTiO₃ 薄膜在室温固态制冷方面可能具有较好的应用前景.     

Atomic layer deposition of Cr2O3 thin films: Effect of crystallization on growth and properties

Atomic layer deposition of Cr₂O₃ thin films from CrO₂Cl₂ and CH₃OH on amorphous SiO₂ and crystalline Si(1 0 0) and -Al₂O₃() substrates was investigated, and properties of the films were ascertained. Self-limited growth with a rate of 0.05–0.1 nm/cycle was obtained at substrate temperatures of 330–420 °C. In this temperature range epitaxial eskolaite was formed on the -Al₂O₃() substrates. The predominant crystallographic orientation in the epitaxial films depended, however, on the growth temperature and film thickness. Sufficiently thick films grown on the SiO₂ and Si(1 0 0) substrates contained also the eskolaite phase, but thinner films deposited at 330–375 °C on these substrates were amorphous. The growth rate data of films with different phase composition allowed a conclusion that the crystalline phase grew markedly faster than the amorphous phase did. The amorphous, polycrystalline and epitaxial films had densities of 4.9, 5.1 and 5.1–5.3 g/cm³, respectively.