Phase transitions in CuBiP2Se6 crystals

Investigation results of dielectric (20?Hz–1?MHz) properties of layered CuBiP₂Se₆ crystals are presented. The temperature dependence of the static dielectric permittivity reveals the first-order “displacive” antiferroelectric phase transition at T _c?=?136?K. In the paraelectric phase, at low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 2473?K (0.21?eV). In the antiferroelectric phase the electrical conductivity and its activation energy (531.1?K (0.045?eV)) are considerably smaller. At low temperatures, the temperature behaviour of the distribution of relaxation times reveals complex freezing phenomena. A part of long relaxation time distribution is strongly affected by external direct current (DC) electric field and it is obviously caused by antiferroelectric domain dynamics.     

Effect of TiO2 addition on the crystallization of quenched glasses in the SiO2–Al2O3–ZrO2 system

The glass formation in the SiO₂-rich region of the ternary oxide system Al₂O₃–ZrO₂–SiO₂ with MgO, CaO, and TiO₂ as melting aids was analyzed. The crystallization of glasses with different content of TiO₂ and phase evolution with the temperature was studied by X-ray diffraction, infrared, laser Raman spectroscopy and transmission electron microscopy. The use of TiO₂ favored formation and crystallization of the glasses due to the decrease of the viscosity of melts and acting as a nucleating agent. The crystalline phase of t-ZrO₂ was developed at temperatures as low as 880°C whereas in as prepared specimens without TiO₂ its presence was not detected. For the specimens with TiO₂, t-ZrO₂ and mullite were the principal phases at 1000°C. TiO₂ addition did not change the crystallization sequence but decreased the formation temperature of the crystalline phases. Most of Ti⁴⁺ ions entered into t-ZrO₂ and only a small portion in mullite, but the surplus was detected in ZrTiO₄.     

The studies of high-temperature and short-time annealing,phase transition process,and magnetic property for LaFe11.7Si1.3 compound

The high-temperature phase transition is analyzed according to the DSC of as-cast LaFe_11.7 Si_1.3 compound and the X-ray patterns of LaFe_11.7Si_1.3 compounds prepared by high-temperature and short-time annealing. Large amount of 1:13 phase begins to appear in LaFe_11.7Si_1.3 compound annealed near the melting point of LaFeSi phase (about 1422?K). When the annealing temperature is close to the temperature of peritectic reaction (about 1497?K), the speed of 1:13 phase formation is the fastest. The phase relation and microstructure of the LaFe_11.7Si_1.3 compounds annealed at 1523?K (5?h), 1373?K (2?h)?+?1523?K (5?h), and 1523?K (7?h) +1373?K (2?h) show that longer time annealing near peritectic reaction is helpful to decrease the impurity phases. For studying the influence of different high-temperature and short-time annealing on magnetic property, the Curie temperature, thermal, and magnetic hystereses, and the magnetocaloric effect of LaFe_11.7Si_1.3 compound annealed at three different temperatures are also investigated. Three compounds all keep the first order of magnetic transition behavior. The maximal magnetic entropy change ΔS_M (T, H) of the samples is 12.9, 16.04, and 23.8?J?kg^?1?K^?1 under a magnetic field of 0–2?T, respectively.     

飞秒激光作用下全向高反膜破坏的激发过程

设计和制备了全向高反膜SiO₂/TiO₂，研究了它在不同脉冲宽度、不同脉冲能量的飞秒激光作用下的破坏阈值和烧蚀深度.利用发展的抽运-探针方法，研究了抽运脉冲作用下材料中导带电子的超快激发和能量沉积过程，建立并求解了飞秒激光激发材料和材料的激发对抽运光自身反作用的耦合动力学模型.模型较好地揭示了材料破坏的激发过程. 关键词： 飞秒激光 全向高反膜 激发过程 破坏机制     

Mg掺杂PST薄膜的溶胶-凝胶法制备及晶相形成研究

利用溶胶-凝胶法成功制备了Mg掺杂Pb_0.4Sr_0.6Mg_xTi< sub>1-xO_3-x薄膜，利用x射线衍射仪对薄膜的物相和结构进行了分析， 用扫描电子显微镜对薄膜的形貌和断面等进行了观察.研究结果表明，薄膜以立方钙钛矿为 晶相，薄膜中晶相以团聚状颗粒存在，晶相含量受热处理条件和Mg的掺杂量所控制.Mg掺杂 对Pb_0.4Sr_0.6Mg_xTi_1-xO_3-x 薄膜晶相含量的影响与钙钛矿中的氧空位缺陷相关.在一定的掺杂范围内，由掺杂引起晶相 的晶格畸变较小时，体系掺Mg平衡了晶体内本征氧空位引入的电荷不平衡，使晶相更为稳定 ，析晶能力提高，晶体形成量随掺杂浓度的提高而提高.当掺杂浓度达到一定量时， 随着Mg 掺杂浓度增加，一方面使形成晶体时杂质浓度增加造成参与形成晶相的组成含量下降，另一 方面使进入钙钛矿结构的Mg增加，氧空位大量增加使畸变程度提高，形成的晶相不稳定，析 晶能力下降，晶体含量随掺杂Mg浓度的增加而不增反降.在相同条件下制备的Pb_{0.4Sr0.6MgxTi1-xO3-x薄膜中Mg掺量约为 x=0.01时，得到的钙钛矿相含量最高，本征氧缺陷所带入的正电荷和Mg引入时带入的负电荷 间达到平衡.此外，Mg的掺入还影响到析晶与热处理过程之间的关系.在高Mg掺量范围，Mg含 量越高，形成的晶相越不稳定，热处理时间越长，使热处理过程中分解的晶相量越多，随Mg 掺量越高和热处理时间越长，薄膜中晶相含量越低. 关键词： 溶胶-凝胶法 PST薄膜 Mg掺杂 晶相形成}     

非有机溶剂萃取催化光度法测定锰Mn(Ⅱ)-H2O2-EBT-PEG-2000体系

研究了碱性介质中,利用锰(Ⅱ)催化过氧化氢氧化铬黑T的指示反应。用聚乙二醇-2000非有机溶剂萃取平衡控制反应时间和指示反应进行的程度。通过测量酸性条件下539nm处聚乙二醇-2000相的吸光度,建立了非有机溶剂萃取催化光度法测定痕量锰(Ⅱ)的新方法。方法的线性范围为0.0080~0.55μg.mL-1,检测限为3.0×10-9g.L-1,可用于铝合金、茶叶样品中锰的测定。     

基于均值漂移实现非发射线天体光谱的谱线自动提取

非发射线天体的光谱是天体光谱谱线提取中最难处理的一种。针对非发射线天体,给出了一种基于均值漂移的谱线自动提取方法。首先,利用均值漂移总是指向局部密度最大点也即密度的模式点这一性质,提取出较为满意的伪连续谱;其次,均值漂移滤波同时工作在空间域和幅度域上,是一种非线性的边缘保持滤波方法,在去除噪声的同时,能够较好地保持特征谱线的信息,文章在连续谱归一化后,采用均值漂移去噪得到谱线光谱;最后,对谱线光谱设置局部阈值提取出特征谱线。通过对恒星、正常星系等的实验表明：该方法是有效的, 这将对后续的参数测量和基于谱线的光谱分类非常有利。     

仿视觉过程的相位展开方法

在所有基于条纹分析的光学测量中,相位展开问题是难以避免的问题。所有传统的相位展开方法的共同点都是在相主值图中通过邻域内相主值差和寻找无噪声的相位展开路径来完成的。如果不利用整幅图像像素间的联系,则误差会沿展开路径传播。根据人眼识别栅线图周期的过程提出了一种与以往完全不同的相位展开方法。经过初步提取周期分界线、修补分界线和根据分界线确定周期三个步骤即可完成相位展开过程。该算法的原理简单明了,实现起来相对简单,只需单幅条纹图像即可得到周期,因而可用于动态测量。实验结果验证了该算法的可行性。     

超细激光束准直器设计的新数学模型

为了获取长距离超细激光束，采用几何能量守恒法设计出一种衍射光学元件，推导出高斯光入射时衍射光学元件位相函数。根据建立的数学模型，设计超细激光束准直器，并模拟高斯光入射时出射激光束的光斑形状及光强分布，最后计算了能量利用率。     

3ω法加热/测温膜中温度波解析及其在微/纳米薄膜导热系数测量中的应用

给出了3ω法测试系统中描述薄膜表面加热/测温膜中温度波动的级数形式解，并将复数温度波动的实部和虚部分开表示.利用该解分析了交流加热频率、加热膜宽度和材料热物性的组合参数对加热膜温度波动幅度的影响.并根据此解对测量原理的数学模型进行了修正，建立了相应的3ω测试系统，首先测定了厚度为500 nm SiO₂薄膜的导热系数，验证了实验系统的合理性.加大了测试频率，利用级数模型在高频段直接得到SiO₂薄膜的导热系数，结合低频段的数据同时确定了Si基体的导热系数.利用级数解分析测试了激光晶体Nd:YAG〈111〉面上多层ZrO₂/SiO₂增透膜的导热系数，测试的ZrO₂薄膜的导热系数比体材料小.进行了不确定度分析.结果表明，提出的分析方法可以有效研究微器件表面薄膜结构的导热性能. 关键词： ω法')" href="#">3ω法 微/纳米薄膜 导热系数 微尺度加热膜