共查询到19条相似文献,搜索用时 78 毫秒
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研究了(Ba1-xSrx)(Zn1/3Nb2/3)O3(BSZN)微波介质陶瓷介电常数的非线性变化以及异常的原因。随着系统中Sr(1/3Nb2/3)O3的增多,介电常数的异常是由于氧八面体的畸变导致的相转变(对称性降低)及第二相的生成造成的。未发生相转变前,介电常数的增大可用电介质理论加以解释;发生相转变后,介电常数呈线性下降趋势,符合对数混合定律。 相似文献
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研究了(Ba1-xSrx)(Zn1/3Nb2/3)O3(BSZN)固溶体系统在烧结中生成的第二相,分析了第二相的分布、形貌、形成规律、机理以及对介电性能的影响。研究表明,系统的主晶相为BSZN,同时生成了大量的第二相——Ba5Nb4O15(、Ba5-xSrx)Nb4O15(x=0~5)、Ba2Nb2O7、BaNb2O6等。第二相的生成是由于ZnO的挥发造成的;烧结温度越高、烧结时间越长,ZnO的挥发越多,第二相的含量也越多。第二相的形貌大部分为长方形的板状,样品的表面部分或完全被第二相所覆盖,且有少量呈粒状散布于晶粒之间。第二相的生成会对系统介质损耗产生不利的影响。 相似文献
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利用电子衍射几何构图法确定固体磷酸催化剂中活性相正磷酸硅(Si_3(PO_4)_4)属于三角晶系。其晶格参数a_r=b_r=c_r=9.26(?),α=50°。确定焦磷酸硅(SiP_2O_7)为单斜晶系。其晶格参数a=4.7,b=12.0,c=7.6(?),β=91°。两种活性相的结晶形态明显不同。正磷酸硅呈规则六边形片晶。片晶面的法线为C_h轴方向。焦磷酸硅具有棱柱状外形。棱平行于a方向。而b与c在棱柱的横截面内。 相似文献
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Al3Ni2的一个超结构相郝朝斌王蓉(北京科技大学材料物理系,100083)Al3Ni2(τ3)相是一种空位有序相,实验上已观察到由十次准晶向Al3Ni2的五重畴结构的转变[1],然而,Al3Ni2结构并不满足准晶近似相的大单胞特征[2]。已有工作[... 相似文献
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传统块体Al-Cu合金过饱和固溶体在进行适当工艺条件下的时效处理时,将会出现过饱和固溶体→G.P.(Ⅰ)区→G.P.(Ⅱ)区(或θ")→θ'→稳定的θ相的沉淀序列。但最近的文献报道,纳米Al-Cu合金在退火过程中将不会析出中间亚稳相,稳定的θ(Al2Cu)相将直接从母相晶粒中析出,且主要分布在晶界或三叉晶界处。α(Al)为面向立方晶体(a=0.404nm),θ(Al2Cu)为复杂四方结构(a=0.607nm,c=0.487nm)。对于纳米Al-Cu晶体材料在固溶温度以下等温时效过程中析出的沉淀相微结构的研究尚未见文献报道。本文用透射电子显微镜(TEM)研究不同Cu含量的纳米Al-Cu合金薄膜材料经过时效处理后的沉淀相微结构。 相似文献
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研究了Pb(Mg1/3Nb2/3)O3-PbTiO3晶体的介电、热电和压电性质,温度测量范围为70K~600K。发现它不仅在474K附近有一铁电-顺电相变,而且在180K附近还存在一个铁电-铁电相变。在相变温度区域里,介电、热电和压电都有明显的热滞效应,具有一级相变特性。 相似文献
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棒状液晶分子相变问题的机械旋转模型研究 总被引:2,自引:1,他引:1
综述一种关于棒状液晶材料的分子结构与液晶相的相关关系的研究成果。介绍了有关液晶分子的机械旋转模型。该模型将液晶分子视作一种高速旋转的转子,通过分子参数计算,对液晶材料的相变温度和分子结构之间的关系给出了一种全新的解释。最新研究表明,含氟三苯液晶材料的分子结构中存在slim和fat现象,能够对液晶材料的相变进行合理解释。该模型能够通过简单的模型方法对新型液晶材料的分子设计与合成提供有用的信息。 相似文献
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Heng Wang Aaron D. LaLonde Yanzhong Pei G. Jeffery Snyder 《Advanced functional materials》2013,23(12):1586-1596
Forming solid solutions has long been considered an effective approach for good thermoelectrics because the lattice thermal conductivities are lower than those of the constituent compounds due to phonon scattering from disordered atoms. However, this effect could also be compensated by a reduction in carrier mobility due to electron scattering from the same disorder. Using a detailed study of n‐type (PbTe)1–x (PbSe)x solid solution (0 ≤ x ≤ 1) as a function of composition, temperature, and doping level, quantitative modeling of transport properties reveals the important parameters characterizing these effects. Based on this analysis, a general criterion for the improvement of zT due to atomic disorder in solid solutions is derived and can be applied to several thermoelectric solid solutions, allowing a convenient prediction of whether better thermoelectric performance could be achieved in a given solid solution. Alloying is shown to be most effective at low temperatures and in materials that are unfavorable for thermoelectrics in their unalloyed forms: high lattice thermal conductivity (stiff materials with low Grüneisen parameters) and high deformation potential. 相似文献
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研究了在 Co/Ti/Si结构中加入非晶 Ge Si层对 Co Si2 /Si异质固相外延的影响 ,用离子束溅射方法在Si衬底上制备 Co/Ge Si/Ti/Si结构多层薄膜 ,通过快速热退火使多层薄膜发生固相反应。采用四探针电阻仪、AES、XRD、RBS等方法进行测试。实验表明 ,利用 Co/Ge Si/Ti/Si固相反应形成的 Co Si2 薄膜具有良好的外延特性和电学特性 ,Ti中间层和非晶 Ge Si中间层具有促进和改善 Co Si2 外延质量 ,减少衬底耗硅量的作用。Ge原子的存在能够改善外延 Co Si2 薄膜的晶格失配率 相似文献
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Qian Wang Youdi Gu Wenxuan Zhu Lei Han Feng Pan Cheng Song 《Advanced functional materials》2021,31(50):2106765
Transition-metal perovskite oxides constitute a series of functional material systems for electronics, catalysis, and energy-conversion processes, in which oxygen migration and evolution play a key role. However, the stable metal–oxygen (M O) bond forms a large energy barrier inhibiting ion diffusion. Therefore, seeking efficient and facile approaches to accelerate oxygen kinetics has become a significant issue. Here, the interaction (interfacial charge transfer and cooperative bonding) between noble metal (Pt, Ag) and perovskites oxide (SrCoO3−δ) is employed to weaken the (M O) bond and decrease the energy barrier of oxygen migration. Noble metal layers serving as oxygen pumps can continuously extract oxygen from oxide films to the atmosphere. The temperature of the topotactic phase transition from perovskite (SrCoO3) to brownmillerite (SrCoO2.5) is remarkably lowered from ≈200 °C to room temperature. Furthermore, this approach can also be applied to SrFeO3 for similar topotactic phase reduction by moderate thermal activation. The finding of this study paves a promising and general pathway to achieve fast oxygen migration in perovskite oxides, with important application prospects in low-temperature electrodes and high-activity catalysis interface. 相似文献