Photo-induced effect in the layered perovskite manganite La_(1.2)Sr_(1.8)Mn_(1.8)Co_(0.2)O_7

1IntroductionWiththediscoveryofcolossalmagnetoresistance(CMR)effectinmanganites,hole-dopingperovskitemanganiteswithunusualelectronictransportandmagneticpropertieshaveattractedconsiderableattention.Thesepropertiesresultfromanintrinsicinteractionbetweencharge,spin,orbitalandlatticedegreesoffreedomthatarestronglycoupledtoeachother[1—6].DoubleexchangemodelcombinedwithJohn-Tellereffectwasusedtoexplainthesepropertiespartly[7—9].InordertogetbetterunderstandingofthemechanismofCMReffect,externals…     

Anisotropic phonon thermal transport in two-dimensional layered materials

Two-dimensional layered materials (2DLMs) have attracted growing attention in optoelectronic devices due to their intriguing anisotropic physical properties. Different members of 2DLMs exhibit unique anisotropic electrical, optical, and thermal properties, fundamentally related to their crystal structure. Among them, directional heat transfer plays a vital role in the thermal management of electronic devices. Here, we use density functional theory calculations to investigate the thermal transport properties of representative layered materials: β-InSe, γ-InSe, MoS₂, and h-BN. We found that the lattice thermal conductivities of β-InSe, γ-InSe, MoS₂, and h-BN display diverse anisotropic behaviors with anisotropy ratios of 10.4, 9.4, 64.9, and 107.7, respectively. The analysis of the phonon modes further indicates that the phonon group velocity is responsible for the anisotropy of thermal transport. Furthermore, the low lattice thermal conductivity of the layered InSe mainly comes from low phonon group velocity and atomic masses. Our findings provide a fundamental physical understanding of the anisotropic thermal transport in layered materials. We hope this study could inspire the advancement of 2DLMs thermal management applications in next-generation integrated electronic and optoelectronic devices.     

Mechanism of formation of nanosized copper particles in a nanoreactor based on the [LiAl<Subscript>2</Subscript>(OH)<Subscript>6</Subscript>]<Subscript>2</Subscript>[Cuedta]·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O supramolecular system

The formation of nanosized copper particles in a nanoreactor based on the [LiAl₂(OH)₆]₂[Cuedta]·nH₂O supramolecular system [Li-Al-Cu(edta)] was studied by the DTA, XRPA, FMR, IR, and mass spectrometry methods. Thermal decomposition of Li-Al-Cu(edta) below 200°C occurs as two-stage removal of the interlayer water molecules. Above 200°C dehydration of [LiAl₂(OH)₆]⁺ metal hydroxide layers occurs simultaneously with destruction of [Cuedta]^2? complexonate ions. The first stage of destruction (below 250–260°C) is a redox process that forms metallic copper and liberates gaseous carbon oxide and dioxide. At higher thermolysis temperatures, other gaseous products evolve (ammonia, hydrogen). The copper phase appeared during thermal decomposition as 20–50 nm isometric particles on the surface, while lenslike copper nanoparticles formed in the bulk substance.     

MAX 相陶瓷的结构、制备及物理性能研究

MAX 相陶瓷因具有独特的 MX 片层与A 片层交替堆叠的晶体结构,使其兼具金属和陶 瓷的优良特性,如良好的导热导电性、可加工性,同时具有良好的抗氧化性、耐腐蚀性以及耐 摩擦磨损等性能,具有非常广泛的应用前景。本文首先介绍了 MAX 相陶瓷材料的种类与晶体 结构,并简述了近几年新发现的 MAX 相陶瓷材料以及制备手段的发展动态。之后从 MAX 相 物理性能的角度出发,重点综述了几种典型 MAX 相陶瓷材料的弹性性能、电学性能、热学性 能、磁性能以及抗辐照性能的研究进展。此外,进一步介绍了MAX 相的二维衍生物 MXene 的 衍生过程、超导性以及其在电化学储能、催化领域的研究进展。最后,本文从探索 MAX 相材 料新结构的多样性、MAX 相物理性能及相关理论计算、MXene 二维材料以及相应的制备、表 征和应用等方面,展望了 MAX 相陶瓷材料的潜在研究方向及应用前景,为 MAX 相和 MXene 材料的深入研究提供了新的思路。     

分层介质中Love波的扩展W-W算法

应用精细积分法(PIM)和扩展Wittrick-Williams(W-W)算法求解横观各向同性分层半空间中的Love波问题.Love波对应于波数-频率域线性常微分方程的本征值问题.精细积分法是求解线性常微分方程两端边值问题和初值问题的高精度算法.利用本征值计数技术,扩展W-W算法可以不遗漏地找到所有本征值.因此,文中使用的方法可以得到计算机精度意义下的精确解.     

EXACT THERMO-ELECTRO-ELASTIC SOLUTION OF FUNCTIONALLY GRADED MULTILAYERED ONE-DIMENSIONAL QUASICRYSTAL CYLINDRICAL SHELLS 1)

两种或多种不同性质材料组成的层状结构可以满足工业发展的需求. 然而, 材料属性在接触面的突变问题, 容易导致层间界面处产生应力集中、裂纹以及分层等问题. 功能梯度材料利用连续变化的组分梯度来代替突变界面, 可以消除界面处的物理性能突变, 提高结构的粘结强度. 本文以一维准晶功能梯度层合圆柱壳为研究对象, 利用类Stroh公式和传递矩阵方法, 建立了材料参数沿径向呈现幂函数变化的层合圆柱壳模型, 获得了简支边界条件对应的一维准晶功能梯度层合圆柱壳的热电弹性精确解. 数值算例中讨论了层合圆柱壳内外表面承受温度载荷时, 功能梯度指数因子对温度场、电场、声子场和相位子场的影响, 尤其是对层合圆柱壳内外表面的影响. 结果表明, 指数因子改变了材料参数的空间分布情况, 进而对温度场、电场、声子场和相位子场都有影响; 增加功能梯度指数因子, 可减小温度载荷引起的内表面变形, 进而提升结构强度. 本文得到的结果可以为功能梯度准晶层合圆柱壳的设计和制造提供可靠的理论依据.     

分层总和法在群桩非线性分析中的应用——变形总和法

本文提出了分层土中承台－桩－土共同作用非线方法，分析了群桩的工作状态和破坏特性，讨论了荷载水平对桩土结点屈服顺序的影响，以及荷载由角桩向内桩的传递规律，桩土载体 分担等问题。并经实例验证，本文提出的群桩分析具有较好的可行性。     

Ce-TZP和Ce-TZP/Al_2O_3层状复合材料受载裂尖的相变特性

用云纹干涉法研究了带直通切口的Ｃｅ ＴＺＰ（Ｔｅｔｒａｇｏｎａｌ ＺｉｒｃｏｎｉａＰｏｌｙｃｒｙｓｔａｌ）和Ｃｅ ＴＺＰ／Ａｌ２Ｏ３层状复合材料三点弯曲梁的相变过程．实验发现１６００°Ｃ／３ｈ烧结１２％ｍｏｌＣｅＯ２稳定的Ｃｅ ＴＺＰ在室温下就具有强烈的自催化效应，直通切口前缘的相变区呈树枝状，Ｃｅ ＴＺＰ／Ａｌ２Ｏ３层状复合材料的自催化相变被Ａｌ２Ｏ３层抑制，切口前缘的相变区变短，且相变区的覆盖面积减小．文中最后对Ａｌ２Ｏ３层改变Ｃｅ ＴＺＰ相变区及力学性能的原因进行了讨论．     

用边界元方法分析复合材料中的裂纹问题

利用层状材料的广义Klevin基本解，建立了计算三维层状材料中的裂纹边界元方法。采用边界元方法中的多区域方法和能反映均匀介质中裂纹尖端应力场和位移场特征的面力奇异单元。裂纹的应力强度因子由裂纹面上的位移经插值计算得到。算例分析表明，本文建议的方法可以获得较高的计算精度。     

Design of a transversely layered cantilever of minimum mass under specified maximum-deflection constraint

The problem of optimal design of a transversely layered cantilever beam of minimum mass composed of a finite set of elastic homogeneous isotropic materials is considered for the case where a constraint is imposed on the maximum deflection of the beam and information on the loads applied to the beam is incomplete. It is shown that, among these loads, there exists the “worst” point load whose magnitude is equal to the resultant of the forces applied to the beam, for which the deflection is maximal for any material distribution along the beam. The necessary optimality conditions are obtained for the mass-minimization problem of the beam under the “worst” loading, a numerical algorithm is developed for the synthesis of the optimal cantilever, and a numerical example is given. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 104–110, July–August, 2007.