Analysis of thermally activated formation and breakdown of Kear-Wilsdorf barriers in Ni<Subscript>3</Subscript>Ge single crystals of various orientations

The orientation dependence of the yield stress in Ni₃Ge single crystals has been examined both theoretically and experimentally. The positive temperature dependence of the yield stress in the low temperature region is attributed to formation of Kear-Wilsdorf barriers. The forces driving the formation and breakdown of barriers are calculated within the framework of the Hirsch scheme. A distinctive feature of the model proposed is that the barrier is considered on the screw component of the a/2[ 01](111) superdislocation in the primary octahedral plane. The major role in barrier formation belongs to anisotropy of elastic moduli, energy of antiphase boundaries in the octahedral plane, shear stresses in the cubic and octahedral planes, and friction-induced stress in the cubic plane. A comparison of predicted values of the driving force of barrier formation and breakdown with experimental values reveals their good agreement. An analysis of the orientation dependence of the driving force of barrier formation in the temperature range T = 77–293 K shows that the dependence (T) has an extremum for crystals deformed along the [ 39] crystallographic direction, which is confirmed experimentally.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 116–125, January–February, 2005.     

High Temperature Phase Transitions in Na_xCoO_2 Materials

1 INTRODUCTION In recent years, much attention has been focused on the NaxCoO2 system due to its notable properties and potential technologic applications as a cathode material in high-energy density, reversible solid state battery systems[1, 2]. Recently, large thermoelectric power[3～6] in NaxCoO2 and superconductivity (～4 K) in hydrated NaxCoO2yH2O (x = 0.35, y = 1.33) ma- terial have been observed[7]. This hydrated layered phase is the first 3d-transition metal oxide with superco…     

金属-有机框架衍生中空超级结构的研究进展:合成与应用（英文）

金属-有机框架(MOF)衍生功能材料的合理设计对于其应用具有重要意义.以简单MOF衍生物为基本单元组装成中空超级结构(HSSs)是提升材料性能的有效策略.目前关于MOF衍生物的综合评述已有诸多报道,然而鲜少针对HSSs的构筑和应用.本文系统总结了MOF衍生HSSs相关研究的最新进展.首先,根据结构差异将MOF衍生HSSs分为5种类型;其次,总结了由MOF衍生物构建HSSs的策略,着重阐述如何设计MOF前驱体和选择转化条件;随后,展示了MOF衍生HSSs在能源和催化相关领域的一些应用;最后,提出了MOF衍生HSSs研究领域所面临的挑战和机遇,旨在为MOF衍生材料的结构设计和性能强化提供一些思路.     

Crystal structure of La0.4Sr0.6CoO2.71 investigated by TEM and XRD

The structure of the oxygen-deficient perovskite La_0.4Sr_0.6CoO_3−δ (δ=0.29) was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Domains between 50 and 250 nm in size were observed in the electron microscope. Weak superstructure reflections were found with both X-ray and electron diffraction. Investigations of these superstructure reflections by selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED) showed that the domains in a crystal are orientated in a 90° relationship. High-resolution transmission electron microscopy (HRTEM) images from the domain boundary also revealed a 90° orientation dependency. Using the symmetry of CBED patterns, the point group 4/mmm was determined. By comparing reflections from the SAED pattern with possible reflections, the space group I4/mmm (No. 139) could be isolated and finally the crystal structure was refined by Rietveld refinement.     

音乐文化发展受经济基础制约的阶段性分析——从唯物辩证法角度看20世纪以来中西音乐关系的变迁

经济基础决定上层建筑,作为上层建筑的音乐文化也必然受到经济基础的制约。自20世纪以来,从百年音乐历史进程中的中西音乐关系来看,不论是强调＂国乐＂、崇尚＂西乐＂抑或提倡＂中西合璧＂,都是经济、政治发展到一定阶段的大势所趋。作为上层建筑,音乐文化具有一定的独立性,它会或早或迟地反映其经济基础,而非亦步亦趋,同时它也会不同程度上影响其经济基础的发展。     

Elementary submodels of parametrizable models

We introduce the notion of F-parametrizable model and prove some general results on elementary submodels of F-parametrizable models. Using this notion, we can uniformly characterize all elementary submodels for the field of real numbers and for the group of all permutations on natural numbers in the first order language as well as in the language of hereditarily finite superstructures. Assuming the constructibility axiom, we obtain a simpler characterization of elementary submodels of F-parametrizable models and prove some additional properties of the structure of their elementary submodels.     

Nonstoichiometric compounds: A critique of current structural views

The current status of experimental knowledge and theoretical views about nonstoichiometric compounds and heteroionic solid solutions is briefly surveyed, particularly in relation to structural aspects. It is emphasised that there is a little understood transition from the state adequately described by point defect theory, valid for very small deviations from ideal stoichiometry, to the highly organised local structure of crystals with a high formal concentration of defects. The role of short range ordering effects, of microdomains of modified, ordered structure and of defect clusters in different systems is considered. Orderdisorder transformations undergone by nonstoichiometric phases at high temperatures present a special problem. The high temperature phases have very high formal defect concentrations, and the site correlation coefficients found experimentally differ but little from those predicted for completely random structures, although the high defect concentrations imply that all the factors promoting short range ordering must be strong. Theoretical developments are considered. Treatments of pair interaction effects, and calculations of the energetics of defect interaction and the reconstructive formation of defect clusters hold some promise for theoretical development.     

Organogels Derived from Potassium 8-Nitroquinolinecarboxylate

A new class of organogels derived from potassium 8-nitroquinolinecarboxylate was selectively formed in THF/MeOH （V：V=1： 1）, and their superstructures were characterized by atomic force microscopy, scanning electron microscopy and transmission electron microscopy.     

X-Ray Diffraction Study of Aluminum Monoxycarbide

The structural characteristics of aluminum monoxycarbide Al₂OC are refined and systematized. Based on our X-ray diffraction data, three modifications of Al₂OC: -Al₂OC, '-Al₂OC, and '-Al₂OC have been revealed. Structural models are suggested for them.     

Small angle scattering of partially oriented polymers: model calculations with monoclinic macrolattice

A three-dimensional monoclinic paracrystalline macrolattice is used to calculate the small angle X-ray scattering pattern of partially oriented polymers with rotational symmetry about the fiber axis. The influence of the crystallite size, the lattice parameters, the lattice distortions and the orientation relative to the fiber axis on the diffraction patterns is studied.Dedicated to Prof. R. Bonart on the occasion of his 60th birthday.