高压结晶PET/PC共混体系中大尺寸聚合物伸直链晶体的形态观察

 大尺寸聚合物伸直链晶体在低维体系物理学的研究中具有不可替代的重要作用。但以往高压合成的聚合物伸直链晶体,尺寸较小且合成时间过长,使其作用至今未能显现。加入10%（质量分数）聚碳酸酯（PC）于聚对苯二甲酸乙二醇酯（PET）中,在研究PET/PC共混体系高压结晶行为的过程中快速合成了大量生长厚度超过100 μm 的聚合物伸直链晶体,并采用扫描电子显微镜对其进行了深入研究。研究表明,高压结晶PET/PC共混体系中存在不同类型的大尺寸伸直链晶体：完善的伸直链晶体、沿平行或垂直于C轴方向发生断裂的伸直链晶体、内聚能密度较大而发生内聚破裂的伸直链晶体、不同断裂方式下呈不同形态的楔形状伸直链晶体以及弯曲的伸直链晶体。同时对不同形态伸直链晶体的形成机理作了阐述。     

多原子极性晶体中表面激子的性质

本文研究多原子极性晶体中表面激子的性质.采用微扰法导出表面激子的有效哈密顿量.多支LO声子对表面激子的自陷能和有效势的影响是相互独立的.对于Wannier激子,电子、空穴间的相互作用的有效势仍是库仑型的,只是介电常数约化为 .多支LO声子的作用使激子的自陷能更低.并得到激子的自陷条件.     

Ferromagnetic films with magnon bandgap periodic structures: Magnon crystals

A new type of photonic crystals is proposed. The new crystals have a forbidden gap in the microwave spectrum of magnetostatic spin waves, and, by analogy with photonic crystals, they are called magnon crystals. Specimens of such crystals were fabricated on the basis of yttrium iron garnet films. The surfaces of ferromagnetic films containing two-dimensional etched hole structures were studied by atomic force and magnetic force mag-netometry. The propagation of spin waves through the magnon crystals was investigated.     

平面波展开法计算二维磁振子晶体带结构

磁振子晶体是光子晶体或声子晶体在磁性材料领域内的替代品,是近来的一个研究热点. 本文提出了磁振子晶体领域内的一种平面波展开法,其较传统的平面波展开法能节约一半以上的计算时间. 采用此方法,数值计算了由Fe/EuO二种铁磁材料构成的二维磁振子晶体带结构. 数值计算结果表明,在一定的体积填充率下,有自旋波带隙的出现;影响磁振子晶体带隙结构形成的主要因素是有效场中的交换作用场,其他作用场的影响相对很小. 关键词： 磁振子晶体 带隙 平面波展开法     

Investigation on emitting centers in naphthalene-benzophenone mixed crystals

In this paper we investigate the nature of naphthalene phosphorescence in naphthalene-benzophenone mixed crystals. A first study of this emission with temperature change leads us to assume the presence of isolated naphthalene molecules in naphthalene crystals doped with benzophenone molecules. Then we investigate the benzophenone-naphthalene coupling in these crystals. After a short recall of theoretical results, we show that benzophenone-naphthalene coupling is the same with naphthalene doped crystals as with benzophenone doped crystals. These conclusions confirm the previous statement that there exist isolated naphthalene molecules in naphthalene crystals doped with benzophenone molecules.     

Multi-step damage accumulation in irradiated crystals

This article presents a model of damage accumulation in irradiated crystals. This model is based on the assumption that the damage accumulation occurs through a series of structural transformations triggered by the destabilization of the current structure of crystals. Formal equations describing the damage accumulation build-up and experimental assessment of the model are presented and discussed in the framework of the actual knowledge of radiation effects in oxide crystals (yttria-stabilized zirconia (YSZ) and magnesium-aluminate spinel (MAS)), silicon carbide crystals and zirconia implanted nickel crystals.     

Electric field in two-dimensional complex plasma crystal:Simulated lattices

We focus on molecular dynamics simulated two-dimensional complex plasma crystals. We use rigid walls as a confinement force and produce square and rectangular crystals. We report various types of two-row crystals. The narrow and long crystals are likely to be used as wigglers; therefore, we simulate such crystals. Also, we analyze the electric fields of simulated crystals. A bit change in lattice parameters can change the internal structures of crystals and their electric fields notably. These parameters are the number of grains, grains charge, length, and width of the crystal. With the help of electric fields, we show the details of crystal structures.     

Compressive energy of ions in ionic crystals

The possibility of writing the repulsive energy in the Born model of binary ionic crystals as a sum of two separate contributions from the two ions has been investigated. Such an approach leads to two identities, one connecting the lattice spacings of a family of ionic crystals and the other connecting their compressibilities. These identities have been tested on the alkali halide crystals over a range of pressures. The agreement is found to be quite satisfactory. Some further predictions with respect to crystals which exist as two polymorphs have also been tested. In all cases, the deviations of the experimental values from the exact identities can be traced to the fact that second neighbour repulsions in the crystals have been neglected. It is hence concluded that individual compressive energies for ions in ionic crystals is a very attractive possibility.     

极化子在正弦色散声子场中的性质

本文计及纵光学声子的色散,在正弦近似下,用微扰法了多原子晶体中极化子的基态能量,有效质量和自能。     

Yb:Y3Al5O12/Y3Al5O12复合晶体的制作和光谱性能

采用热键合技术,制作中运用不同的工艺参量制作出12片Yb:Y3Al5O12/Y3Al5O12(Yb:YAG/YAG)复合.晶体.利用偏光显微镜对其键合界面进行了观察,研究了样品的透射光谱,从而确定出复合晶体合适的制作工艺.通过透射光谱的形状和透射率来表征复合晶体键合界面的质量.研究表明Yb:YAG/YAG复合晶体键合质量较好,可实现一体化.     

Crystallization in two-component Coulomb systems

The analysis of Coulomb crystallization is extended from one-component to two-component plasmas. Critical parameters for the existence of Coulomb crystals are derived for both classical and quantum crystals. In the latter case, a critical mass ratio of the two charged components is found, which is of the order of 80. Thus, holes in semiconductors with sufficiently flat valence bands are predicted to spontaneously order into a regular lattice. Such hole crystals are intimately related to ion Coulomb crystals in white dwarf and neutron stars as well as to ion crystals produced in the laboratory. A unified phase diagram of two-component Coulomb crystals is presented and is verified by first-principles computer simulations.     

Electronic structure calculations of lead tungstate PbWO 4 crystals with defects of molybdenum impurity

Lead tungstate PbWO 4 crystals are one of the most effective scintillation materials for calorimetric devices designed to detect elementary particles with extremely high energies [1]. The interest to PbWO 4 scintillation and luminescence properties increased noticeably in the recent years [1, v 2]. However, experimental results obtained for PbWO 4 optical properties, substantially differ for crystals, produced under different growing conditions. Such a variety led to the situation, that up to now there are no generally accepted explanations for the origin of luminescence centres in PbWO 4 . The electronic structure of possible luminescent centres in perfect lead tungstate crystals PbWO 4 and in the crystals with molybdenum impurity PbWO 4 :Mo is ab-initio calculated in order to elucidate the origin of luminescence in lead tungstate crystals. Conclusions concerning excitation of self luminescence in perfect crystals and defect luminescence in Mo-doped crystals are made on the basis of results of calculations and experimental data on luminescence and photo excitation of PbWO 4 and PbWO 4 :Mo crystals.     

Investigation of the phase transitions of ferroelectric KIO3 and KNbO3 crystals by optical diffraction

Optical diffraction is reviewed as a technique for investigation of the phase transitions in crystals with a multidomain structure. It has been used to study the phase transitions in KIO₃ and KNbO₃ single crystals. Strong optical diffraction bands resulted from electric domains in KNbO₃ crystals and their change with temperature were observed when a laser beam passed through the crystals. The diffraction patterns observed changed abruptly at 427°C, 223°C, and -50°C respectively, at which KNbO₃ crystals undergo structural phase transitions. It is considered that the change of the diffraction patterns with temperature is due to change of the electric domains in the crystals.     

Elastic waves in cubic crystals with positive or negative anisotropy of second-order elastic moduli

Elastic waves in cubic crystals are considered. A new classification of cubic crystals is proposed based on their elastic properties. All cubic crystals are shown to be divided into crystals with a positive or negative anisotropy of their second-order elastic moduli. The vibrational-branch spectra of crystals of these two types differ qualitatively in shape. The angular dependences of the polarization vectors are analyzed. The transverse component in quasi-longitudinal vibrations in cubic crystals is shown to be small and can be neglected. The longitudinal component in quasi-transverse modes is not small: its maximum value is 16.5% for Ge and reaches 27% for KCl.     

Isolation of extended-chain crystals from high-pressure crystallized polyethylene by selective dissolution

In recent years the formation of extended-chain crystals has received increasing attention, and a number of mechanisms for it have been proposed [1–5]. These mechanisms are classified into two groups, one being the thickening of folded-chain crystals [1, 2] and the other being the direct formation of extended-chain crystals from the melt [3–5]. In order to clarify the mechanism, it is necessary to study the microstructure of the isolated extended-chain crystals in detail. In this paper the isolation of the extended-chain crystals from high-pressure crystallized polyethylene by selective dissolution of folded-chain crystals is described.     

Electrical properties of LiNbO3 crystals reduced in a hydrogen atmosphere

The temperature dependence of the electrical conductivity and pyroelectric coefficient of lithium niobate crystals reduced in a hydrogen atmosphere has been studied. It has been established that the activation energy of dark electrical conduction in these crystals in the temperature range 288?C350 K differs from the corresponding values for crystals reduced in vacuum and is equal to 0.68 ± 0.02 eV. It has been shown that the annealing of LiNbO₃ crystals in a hydrogen atmosphere hardly affects their pyroelectric properties. The mechanism of electrical conduction of LiNbO₃ crystals reduced in a hydrogen-containing atmosphere has been discussed.     

A method of designing photonic crystal grating slow-wave circuit for Ribbon--Beam microwave travelling wave amplifiers

A method of designing a photonic crystal grating slow-wave circuit in which the cylinders of the 2D photonic crystals dot on a cross-sectional plane is established by calculating the band structures of the 2D photonic crystals, and the eigenfrequency of the equivalent waveguide grating. For calculating the band structures, the eigenvalue equations of the photonic crystals in the system of photonic crystal grating slow-wave circuit are derived in a special polarization mode. Two examples are taken to show the method. The design result is validated by the scattering parameters of the same circuit. The result indicates that there exists no photonic band gap if the metal gratings do not extend into the photonic crystals; the design of the circuit without the metal gratings extending into the photonic crystals is less flexible than that with the metal gratings extending into the photonic crystals.     

Beyond butterflies—the diversity of biological photonic crystals

When biological photonic crystals are discussed, butterfly photonic crystals are often cited as representative; in fact, numerous diverse biological photonic crystals exist and butterfly photonic crystals have several quirks when compared with others, with the consequence that considering them typical is in many ways unhelpful. In this paper, we give an overview of biological photonic crystals and discuss their typical features, specifically with regard to their periodicities, geometries, chemical compositions, the wavelengths they reflect and their band gaps. The low refractive index contrast and low mean refractive index: a universal feature of biological photonic crystals compared with artificial ones is highlighted and attention is drawn to their comparatively complex band diagrams.     

Improvement of the scintillation properties of Gd3Ga3Al2O12:Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd₃Ga₃Al₂O₁₂ single crystals to improve the scintillation properties. The crystals of Gd₃Ga₃Al₂O₁₂ codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a ¹³⁷Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photonic flame effect

We observed a new effect which we called the photonic flame effect (PFE). Several three-dimensional photonic crystals (synthetic opals) were posed on a Cu plate at the temperature of liquid nitrogen (77 K). The typical distance between the crystals was 1–5 cm. A long-continued optical luminescence was excited in one of the crystals by the ruby laser pulse. A visible luminescence appeared in the other crystals (not illuminated by the laser pulse), with a time delay with respect to the luminescence in the first crystal (illuminated by the laser pulse) being observed. We examined synthetic opal crystals and those filled with nonlinear liquids.