NH4H2PO4和ND4D2PO4晶体微结构的拉曼光谱研究

本文利用偏振拉曼光谱和第一性原理, 对磷酸二氢铵(NH₄H₂PO₄, ADP)和不同氘含量磷酸二氢铵DADP晶体的晶格振动模式进行了研究. 实验测得了不同几何配置、200–4000 cm^-1范围的偏振拉曼光谱, 分析在不同氘含量条件下921 cm^-1和3000 cm^-1附近拉曼峰的变化. 在ADP晶体中, 基于基本结构单元NH₄⁺ 和H₂PO₄^-基团的振动模, 用第一性原理进行了数值模拟, 进一步明确拉曼峰与晶体中原子振动的对应关系; 通过洛伦兹拟合不同氘含量DADP晶体的拉曼光谱中2000–2600 cm^-1处各峰的变化讨论了DADP 晶体的氘化过程, 结果表明氘化顺序是先NH₄⁺ 基团后H₂PO₄^-基团, 研究结果为今后此类材料的生长和性能优化奠定了基础.     

MgB2超导体的正电子湮没研究

本文利用正电子湮没技术（PAT）对不同密度的MgB2样品分别进行了测定，结果发现正电子在MgB2中自由态的湮没时间（本征寿命τ1）和在捕获态的湮没时间（缺陷寿命τ2）比其他高温超导体都明显要高，这反映了MgB2的体电子浓度相对于其它超导体要低，可能归因于MgB2超导材料本身的晶体结构和化学组成，MgB2超导材料的正电子寿命不仅与晶体的结构缺陷，而且与样品的密度或孔隙度有关．     

MgB2超导体的正电子湮没研究

本文利用正电子湮没技术(PAT)对不同密度的MgB2样品分别进行了测定,结果发现正电子在MgB2中自由态的湮没时间(本征寿命τ1)和在捕获态的湮没时间(缺陷寿命τ2)比其他高温超导体都明显要高,这反映了MgB2的体电子浓度相对于其它超导体要低,可能归因于MgB2超导材料本身的晶体结构和化学组成,MgB2超导材料的正电子寿命不仅与晶体的结构缺陷,而且与样品的密度或孔隙度有关.     

掺镧PbWO4闪烁晶体的缺陷研究

利用正电子湮没寿命谱(PAT)和X射线电子能谱(XPS)研究了掺镧所引起的PbWO₄ 晶体缺陷的变化.结果表明：掺镧后,PbWO₄晶体中的正电子捕获中心铅空位(V< sub>Pb)浓度增加,并进一步诱导低价氧浓度的增加.讨论了掺La的作用机制,认为掺 La将抑制晶体中的氧空位,增加铅空位浓度. 关键词： 掺镧钨酸铅晶体 正电子湮没寿命谱 X射线电子能谱 缺陷     

掺杂Na+的KC1色心激光晶体的正电子湮没研究

本文用正电子湮没方法研究了在掺Na⁺条件下,单纯、附色和γ射线辐照的KC1单晶的湮没寿命以及Doppler展宽S参数与掺Na⁺量的关系.结果表明掺Na⁺量为800ppm的KC1单晶空位浓度最小,为4.24×10¹⁷/cm³,它接近于纯KC1晶体的空位浓度.在附色的KC1晶体中存在明显的F心.S参数主要是受卤族阴离子外层电子的影响.此外还掺Na⁺的KC1单晶正电子湮机制进行了讨论.     

用正电子湮没技术研究a-Si:H/a-SiNx:H多层膜中的界面缺陷

本文报道应用正电子湮没技术(PAT)对a-Si:H/a-SiN_x:H(x≈0.5)多层膜系列样品所进行的研究。发现,由于a-Si:H和a-SiN_x:H在结构方面的失配,导致在a-Si:H/a-SiN_x:H多层膜中的界面区,产生大量缺陷。在a-Si:H子层中,紧靠界面的是应变层,厚度约为8?;在应变层之后是过渡层,厚度约为50?。在过渡层中存在大量缺陷,这就是所谓界面缺陷。 关键词：     

形变充氢多晶纯钴中缺陷的正电子湮没研究

用正电子寿命和多普勒线形参数测量技术,研究了形变和形变充氢多晶钴试样的缺陷性质及其回复行为。观察到形变样品阴极充氢后,氢致缺陷为一定量的位错和空位以及少量的空位团。没有观察到微空洞和微裂纹的产生。单空位的回复温度范围为73—260℃,位错和空位团的退火发生在350—670℃温度范围。测得空位的迁移激活能为E_v^m=1.09±0.07eV。 关键词：     

正电子湮没谱学在金属材料氢/氦行为研究中的应用

用于核反应堆的金属结构材料中氢/氦泡的前躯体——(氢/氦)-空位复合体的形成受到温度、辐照剂量等多方面因素的影响,研究其在材料中的形成和演化行为对气泡形核的理解及先进核反应堆材料的发展起着至关重要的作用.然而,受到分辨率的局限,这种原子尺度的微结构很难用电镜等常规方法进行表征,以致于该问题的研究上可利用的数据相对较少.正电子湮没谱学是一种研究材料中微观缺陷的特色表征方法,近些年来慢正电子束流和新型核探测谱仪技术的不断发展以及基于慢束发展起来的多种实验测试方法的改进,使正电子湮没技术应用已拓展到金属材料中氢/氦行为的研究领域,在金属材料表面氢/氦辐照损伤的研究中发挥了重要作用.本文结合国内外相关进展以及本课题组的一些研究成果评述了正电子湮没谱学在金属材料氢氦行为研究中的应用,着重讨论了正电子湮没寿命谱、多普勒展宽谱、符合多普勒展宽三种测量方法在如下金属材料氢/氦行为研究中的优势:1)氢/氦气泡尺寸和浓度的估算; 2)高能氢/氦离子辐照损伤缺陷及缺陷的退火、时效的演化行为; 3)不同形变程度样品中氢/氦与形变缺陷的相互作用; 4)不同能量或剂量氢/氦离子辐照对材料造成的损伤以及氢氦协同作用...     

NiTi形状记忆合金相变过程的正电子湮没研究

采用正电子湮没技术研究了NiTi合金在降温和升温过程中缺陷和电子密度随温度的变化.在降温过程中,当温度从295K降至225K时,合金的电子密度nb随温度的降低而下降,在225K时降至最小;随后,nb随温度的降低而升高.当温度从295K降至221K时,合金缺陷的开空间随温度的下降而升高,在221K时达到最大值;随后,缺陷的开空间随温度的下降而下降.在升温过程中,当温度从25K升至253K时,合金的电子密度nb随温度的升高而降低,并在253K时达到最小;当温度从253K升至295K时,合金电子密度nb随温度的升高而升高.在相变临界温度点Ms=222K,Mf=197.2K,As=237.5K,Af=255.5K附近,合金的电子密度nb及合金缺陷的开空间均有异常的变化.     

掺钇钨酸铅晶体发光性能和微观缺陷的研究

通过透射谱、X射线激发发射谱（XSL）的测试，研究了Bridgman法生长的掺钇钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和X光电子能谱（XPS）实验手段，对掺钇钨酸晶体的微观缺陷进行研究。实验表明，钇掺杂能够提高钨酸铅晶体的发光快成分比例，并使得晶体中的正电子俘获中心浓度下降，低价氧浓度下降。提出掺钇钨酸铅晶体中钇的掺杂主要以Y^3 占据VPb的形式存在。Y^3 占据VPb可能是钨酸铅晶体吸收边得到改善的原因，而由于晶体内低价氧浓度的减少，作为绿光发光中心的（WO3＋O^-)基团的减少可能会使发光快成分比例有所增加。     

Study of modulation property to incident laser by surface micro-defects on KH2PO4 crystal

KH₂PO₄ crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries (e.g., width, morphology, and depth of defects) are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 μ. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μ for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.     

Study on incident laser modulation using surface micro-defects on KH2PO4 crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.     

Study on incident laser modulation using surface micro-defects on KH₂PO₄ crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion.Modulation of an incident laser by surface micro-defects will induce the growth of surface damage,which largely restricts the enhancement of the laser induced damage threshold.The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method.The results indicate that after the modulation of surface defects,the light intensity distribution inside the crystal is badly distorted,with the light intensity enhanced symmetrically.The relations between modulation properties and defect geometries(e.g.,width,morphology,and depth of defects) are quite different for different defects.The modulation action is most obvious when the width of surface defects reaches 1.064 μm.For defects with smooth morphology,such as spherical pits,the degree of modulation is the smallest and the light intensity distribution seems relatively uniform.The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value.The critical depth is 1.064 μm for cuboid pits and radial cracks,while for ellipsoidal pits the value depends on both the width and the length of the defects.     

Defect characterization of slow-cooled and quenched samples of calcium-copper-titanate through positron annihilation spectroscopy

Abstract

Positron annihilation lifetime and Doppler-broadened gamma-ray spectra have been analyzed for slow-cooled and thermally quenched polycrystalline samples of calcium-copper-titanate. Two positron lifetimes revealing the characteristic defects in the respective samples were carefully analyzed to compare and contrast the significance of their origin and implication. A third component arising from positronium formation at the powdered particle surfaces has been considered in the analysis although its significance is lost in its very small intensity (～ 1.1–1.2%). In the quenched sample, the defect-specific long positron lifetime (τ₂) is found to larger and the mean lifetime smaller while its intensity I₂ is found drastically smaller and the concentration of defects less by an order of magnitude as compared to the slow-cooled sample. The observed changes in electrical parameters of slow-cooled and quenched samples were found to have correlations with the positron annihilation lifetime and Doppler-broadened lineshape parameters.     

Study of the near-field modulation property of microwaviness on a KH2PO4 crystal surface

The KH 2 PO 4 crystal is a key component in optical systems of inertial confinement fusion (ICF).The microwaviness on a KH 2 PO 4 crystal surface is strongly related to its damage threshold which is a key parameter for application.To study the laser induced damage mechanism caused by microwaviness,in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method.Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal;in a common range of microwaviness amplitude,the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm;1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal;the light intensity modulation is just around the microwaviness in the form of an evanescent wave,not inside the crystal when the microwaviness period is below 0.712 μm;light intensity modulation degree has two extreme points in microwaviness periods of 1.064 μm and 1.6 μm,remains unchanged between periods of 3 μm and 150 μm,and descends above the period of 150 μm to 920 μm.     

The Initial Reactions of H3PO4 and NaH2PO4Supported on Silica: A Joint Experimental and Theoretical Study

利用XRD、TG、DRIFTS、31P MAS NMR和密度泛函理论研究了浸渍法制备的硅胶负载型磷酸和磷酸二氢钠催化剂,阐明了催化剂制备过程中生成的初始缩合产物和其反应机理. 光谱试验结果显示,在二氧化硅负载的磷酸上,除了聚磷酸外,还有硅磷酸盐的存在;在二氧化硅负载的磷酸二氢钠上,仅发现聚磷酸钠存在. 密度泛函模拟结果也证明,磷酸与二氧化硅表面硅羟基之间的反应在缩合反应的初始阶段比其自身的二聚反应更为有利. 但是在硅胶负载的磷酸二氢钠上,磷酸二氢钠的二聚和三聚是缩合反应初始阶段的主要反应.     

Anisotropic domain-wall dynamics in proton-irradiated KH2PO4

KH₂PO₄ single crystals have been studied by employing complex impedance measurements in view of the domain freezing effect. As a result, distinct behaviors of the anisotropic domain-wall dynamics in the activation energy of domain freezing and the Vogel–Fulcher temperature before and after proton irradiation have been identified in the anisotropic crystal structure.     

+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

Far infrared reflectivity spectra of a KH2PO4 single crystal

Conclusion The experimental results presented in this paper show that two heavily damped modes, due to proton tunneling, are active in the two phases of KDP: the well-known soft mode which attains a hard-core frequency at the transition temperature and a low frequency mode polarized in a direction perpendicular to the c axis. These modes are responsible for the temperature variation of the low frequency dielectric permittivity in the two crystallographic directions. Due to the size of the samples we do not obtain a single domain crystal, and it was impossible to distinguish the B₁ and B₂ modes. The 200–300 cm^–1 spectral range is very sensitive to the orientation of the incident wave, and certainly corresponds to the hydrogen bonds vibrations.