钙钛矿型复合氧化物LaM_yM_（1－y）~’O_3的结构与红外光谱研究

本文对Ｂ位二元复合钙钛矿型复合氧化物ＬａＭｙＭ１－ｙ’Ｏ３（Ｍ、Ｍ’＝Ｍｎ、Ｆｅ、Ｃｏ；ｙ＝０．０～１．０）的结构和红外光谱进行了研究．Ｂ位元素复合对Ｂ－Ｏ键强度有较大影响，Ｂ位离子之间的相互作用及ＢＯ６八面体畸变所导致的晶体结构的改变在红外光谱上有明显的反映，晶体结构的改变和红外光谱的变化有一定的对应关系．在Ｆｅ－Ｍｎ和Ｆｅ－Ｃｏ体系中，几何因素对Ｂ－Ｏ键伸缩振动频率的变化起主导作用，在Ｍｎ－ＣＯ体系中电子因素起主导作用．     

钙钛矿结构SOFC阴极材料的研究进展

电化学反应能直接将固体氧化物燃料电池(SOFC)中的化学能转换成电能,具有能量转化效率高、环境友好等优点,被认为是极具发展前途的新型高效能源发电技术.早期SOFC工作温度一般在800℃以上,这导致电池寿命缩短、材料成本增加.因此,低温化研发的推进有利于加快SOFC商品化的步伐,而其关键在于开发高性能的阴极材料.然而,工作温度的降低使得电池各组件的欧姆阻抗和极化阻抗急剧增大,尤其是阴极材料.因此,制备氧裂解催化性能高、极化阻抗低和化学稳定性好的阴极材料是提高SOFC电化学性能和长期稳定性的有效途径.大量研究从阴极材料的组成和微观结构入手,以改善传统阴极材料的电化学性能并开发出新型高性能阴极材料,取得了丰硕的成果.而高性能阴极材料之所以还未能实现实际应用,主要受制于其会与电解质反应、CO2污染、相变引起的结构不稳定、与电解质膨胀系数相差大引起的不匹配等问题.进一步研究发现,通过引入相容性好的材料作为阻挡层能够阻碍其与电解质发生反应;优化阴极粉体制备工艺、降低焙烧温度可缓解CO2污染问题;过渡金属元素掺杂可以有效控制阴极材料的相变;在阴极材料中引入膨胀系数较小的电解质材料可以改善其与电解质的匹配性.本文从组成和微观结构的角度,综述了近年来钙钛矿结构SOFC阴极材料的研究进展,并简要分析了阴极材料的组成、微观结构与性能的关系,对今后阴极材料的性能优化和新型阴极材料的开发进行了展望.     

钙钛矿结构固体电解质材料的研究进展

钙钛矿结构固体电解质材料由于其优越的导电性能而被人们发现并广泛研究.综述了SOFC中钙钛矿结构固体电解质材料的研究进展,概述了氧离子导体、质子导体、锂离子导体为代表的钙钛矿结构固体电解质的研究情况以及湿化学法制备中低温下工作的SOFC电解质材料的主要途径.     

具有钙钛矿结构的SOFC用电解质材料的最新研究进展

固体氧化物燃料电池(SOFC)是20世纪80年代迅速发展起来的新型发电技术,能量转换效率可高达70%～80%,被称为21世纪最有前途的绿色能源.主要介绍了固体氧化物燃料电池所用钙钛矿结构电解质材料的研究进展,集中讨论了LaGaO3系、(Ba,Sr)CeO3系和PrGaO3系的结构特性、制备方法、电学性能和应用前景.固体氧化物燃料电池钙钛矿结构电解质材料的发展趋势是:对基质材料进行二元或多元掺杂以形成综合性能更优的复合氧化物;研究和开发与之相适宜的电极材料;进一步提高固体燃料电池的稳定性和能量转换效率.     

正交FeH5结构、力学和电子性质的第一性原理研究

基于密度泛函理论(DFT)对在300 GPa下正交Cmca-FeH5晶体的结构、力学及结构电子特性进行理论研究.获得了Cmca-FeH5的晶格常数和键长,计算结果与之前的理论数据相符合;计算分析了其能带结构和电子态密度,表明压强为300 GPa时Cmca-FeH5呈弱金属性;采用能量-应变(E-S)和应力-应变(S-S...     

双钙钛矿型氧化物基双掺杂碱土金属结构和电阻率性质研究

以A2B'B"O6型氧化物为研究对象,利用溶胶-凝胶法制备出双掺杂La、Ca的(Sr2-3xLa2xCax)Fe-MoO6(0≤x≤0.30)多晶样品,研究了其结构和电阻率性质.通过XRD测试了其结构,结果显示样品质量优良,并分析了其共性与异性.利用SEM观察了其形貌特征,结果显示样品致密性和连通性较好,部分区域有孔洞.利用EDS探测器对样品成分进行了分析,其电阻率呈先减小后增大的趋势,并分析了其变化机理.     

钙钛矿结构氧化物电脉冲诱发可逆变阻机理的研究进展

系统论述了钙钛矿结构氧化物电脉冲诱发可逆变阻效应的非挥发存储机理,对三种物理模型：体效应模型、界面效应模型和导电畴隧穿模型进行了详细讨论,并提出了可逆变阻效应的实用化所面临的关键问题及其发展方向。     

退火对立方相 MgxZn1-xO薄膜的结构和光学性质影响

在蓝宝石（0001）衬底上低温生长立方相MgxZn1-xO（x〉0．5）晶体薄膜，用X射线衍射（XRD）和透射光谱分析高温退火对薄膜的结构和光学性质的影响．结果表明;对Mg0．53Zn0．47O薄膜，在900℃的退火温度下，（0002）衍射峰以及透射光谱上双吸收边的出现均表明有六方结构从其立方结构中分离出来；但对于Mg含量高于55％的样品，即使经历了1000℃的高温退火，也不会有任何相分裂现象出现．而电学测试结果表明，高温下热稳定性良好的立方相Mg0．55Zn0．45O晶体薄膜还能用于金属-绝缘体-半导体的绝缘层，并且漏电流小．由此可以判断，x≥0．55的超饱和MgZn1-xO薄膜具有稳定的立方相晶体结构和优良的光学、电学性质，因而是制作高质量的光电子器件和量子阱激光器的理想材料．     

新型复合钙钛矿Ba(SbⅢ,SbⅤ)O3的水热合成和表征

采用水热晶化法制备了Ｂａ（Ｓｂ^Ⅲ,Ｓｂ^Ⅴ）Ｏ_３新型钙钛矿型氧化物,并通过ＸＲＤ、 ＩＲ、ＳＥＭ和ＩＣＰ等方法对产物物相、形貌和组成等进行了表征．结果表明,产物为立方钙钛矿结构,晶胞参数为α＝０．４１５ｎｍ,粒度为１～２μｍ具有一定团聚的多晶粉末．产物中锑为三价和五价两种价态．水热条件对合成影响的研究结果表明, Ｂａ（Ｓｂ^Ⅲ,ｓｂ^Ⅴ）Ｏ_３合成的适宜碱度和ｎ_{Ｓｂ（Ⅴ)}／ｎ_{Ｓｂ（Ⅲ）}分别为 ８～１０Ｍｏｌ／Ｌ ＫＯＨ和 ０～１     

Analytical Treatment of the Isotropic and Tetragonal Lattice Green Functions for the Face-centered Cubic,Body-centered Cubic and Simple Cubic Lattices

In this paper, we propose an efficient method to calculate the isotropic and tetragonal lattice Green functions for the face-centered cubic (FCC), bodycentered cubic (BCC) and simple cubic (SC) lattices. The method is based on binomial expansion theorems, which provide us with analytical formulae through basic integrals. The resulting series present better convergence rates. Several acceleration techniques are combined to further improve the efficiency of the established formulas. The obtained results for the lattice Green functions are in good agreement with the known numerical calculation results.     

两种重要形貌的碳酸钙的可控合成及生长机理探讨

本文采用碳化法,在改进了气体分布器的自制鼓泡搅拌釜中,以MgCl2和ZnSO4为晶型控制剂制备了不同形貌的碳酸钙。主要讨论了晶型控制剂、碳化温度、CO2流速等因素对碳酸钙形貌的影响,并在此基础上提出了各自的生长机理。产品用SEM、XRD进行形貌观察和晶型分析,结果显示当以MgCl2作为晶型控制剂时,需在高温、低CO2流速的条件下才能制备出结晶度好、文石相含量高的针状碳酸钙;而当采用ZnSO4作为晶型控制剂时,需在低温、高CO2流速条件下才能制备出单一方解石相的立方状纳米级碳酸钙。在最佳条件下制备的针状碳酸钙的粒径为0.5~2μm,长径比为10~20;制备的立方状碳酸钙的粒径为30~80nm。     

Troublesome Crystal Structures: Prevention,Detection, and Resolution

A large number of incorrect crystal structures is being published today. These structures are proving to be a particular problem to those of us who are interested in comparing structural moieties found in the databases in order to develop structure-property relationships. Problems can reside in the input data, e.g., wrong unit cell or low quality intensity data, or in the structural model, e.g., wrong space group or atom types. Many of the common mistakes are, however, relatively easy to detect and thus should be preventable; at the very least, suspicious structures can be flagged, if not by the authors then by the referees and, ultimately, the crystallographic databases. This article describes some of the more common mistakes and their effects on the resulting structures, lists a series of tests that can be used to detect incorrect structures, and makes a strong plea for the publication of higher quality structures.     

Robust Synthesis of Gold Cubic Nanoframes through a Combination of Galvanic Replacement,Gold Deposition,and Silver Dealloying

A facile, robust approach to the synthesis of Au cubic nanoframes is described. The synthesis involves three major steps: 1) preparation of Au–Ag alloyed nanocages using a galvanic replacement reaction between Ag nanocubes and HAuCl₄; 2) deposition of thin layers of pure Au onto the surfaces of the nanocages by reducing HAuCl₄ with ascorbic acid, and; 3) formation of Au cubic nanoframes through a dealloying process with HAuCl₄. The key to the formation of Au cubic nanoframes is to coat the surfaces of the Au–Ag nanocages with sufficiently thick layers of Au before they are dealloyed. The Au layer could prevent the skeleton of a nanocage from being fragmented during the dealloying step. The as‐prepared Au cubic nanoframes exhibit tunable localized surface plasmon resonance peaks in the near‐infrared region, but with much lower Ag content as compared with the initial Au–Ag nanocages.     

Symmetrization of the Crystal Lattice of MAPbI3 Boosts the Performance and Stability of Metal–Perovskite Photodiodes

Semiconducting lead triiodide perovskites (A PbI₃) have shown remarkable performance in applications including photovoltaics and electroluminescence. Despite many theoretical possibilities for A ⁺ in A PbI₃, the current experimental knowledge is largely limited to two of these materials: methylammonium (MA⁺) and formamidinium (FA⁺) lead triiodides, neither of which adopts the ideal, cubic perovskite structure at room temperature. Here, a volume‐based criterion is proposed for cubic A PbI₃ to be stable, and two perovskite materials MA_1?x EA_x PbI₃ (MEPI, EA⁺ = ethylammonium) and MA_1?y DMA_y PbI₃ (MDPI, DMA⁺ = dimethylammonium) are introduced. Powder and single‐crystal X‐ray diffraction (XRD) results reveal that MEPI and MDPI are solid solutions possessing the cubic perovskite structure, and the EA⁺ and DMA⁺ cations play similar roles in the symmetrization of the crystal lattice of MAPbI₃. Single crystals of MEPI and MDPI are grown and made into plates of a range of thicknesses, and then into metal–perovskite photodiodes. These devices exhibit tripled diffusion lengths and about tenfold enhancement in stability against moisture, both relative to the current benchmark MAPbI₃. In this study, the systematic approach to materials design and device fabrication greatly expands the candidate pool of perovskite semiconductors, and paves the way for high‐performance, single‐crystal perovskite devices including solar cells and light emitters.     

Relationship between Primary Crystal Temperature and Carbon Equivalent in Cast Iron

CE （=%C＋（1/3）x（%Si）） does not suit experiment results in many cases. In this work, the effect of alloy elements on primary crystal temperature was measured and the relationship between primary crystal temperature （Tc） and carbon equivalent （CEL） was investigated. The results show that Tc （Celsius degree） = 1650-110 × （%C） -25 × （%Si）＋3 × （%Mn） -35 × （%P） -71 × （%5）-2 × （%Ni） -7 × （%Cr）; CEL=%C ＋ 0.23×（%Si）-0.03× （%Mn）＋0.32×（%P）＋0.64×（%S） ＋0.02×（%Ni）＋0.06×（%Cr）. That is, in hypo eutectic composition, carbon equivalent should be calculated with CEL=%C＋ 0.23×（%Si）, not with CE=%C＋（1/3） x（%Si）.     

LiNbO_3晶体的力学参数与晶面取向间的关系

本实验采用 LiNbO_3 单晶,取四种不同晶面指向的样品进行了力学参数,如断裂强度σ_f、断裂功γ_f、断裂韧性 K_(Ic)和弹性模量 E 的测量。在三点弯曲试验条件下,对 LiNbO_3 单晶不同取向时的声发射特征也作了研究。实验发现,σ_f、γ_f 和 E 与晶面间距、晶面上的离子排列关系较为明显,声发射信号随单晶的取向不同而变化,这是其各向异性结构所致。