首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 101 毫秒
1.
利用同步辐射X射线衍射技术 ,对La0 .3Bi0 .2 Ca0 .5MnO3 中存在的Jahn Teller畸变进行了原位的高压研究。实验表明 ,外加压力能有效地影响到晶格中Mn—O键长和Mn—O—Mn键角的变化。当压力为 1.8GPa时 ,在晶格中存在的两种不同畸变模式之间的相互作用下 ,导致了位于a b基面上的Q2 畸变模式的消失  相似文献   

2.
采用沉淀法制备了α-Fe2O3超微粒,将超微粒粉末在不同温度下进行了高压处理,利用X射线衍射,TEM和穆斯堡尔谱学对高压处理前后的样品进行了研究。结果表明,室温下压力对微晶的晶粒尺寸没有产生明显的影响,热压使晶粒尺寸有较大增长。压力主要对微晶的晶格畸变程度及取向产生了影响  相似文献   

3.
钛酸盐钙钛矿氧化物体系的研究对理解具有铁电极化的功能材料具有非常重要的科学意义.本文对ATiO3(A=Ca,Sr,Ba,Pb,Cd)体系的低温相、结构相变、及其对应的位移模式进行综述.我们着重比较了该体系存在的两类不稳定声子模式,即铁电极化模式(Ferroelectric,FE)和反铁畸变模式(Antiferrodistortive,AFD),在不同体系中所起到的作用.我们举例阐述了晶格失配应变、人工构造超晶格和化学掺杂等方法对这两种模式的调控思路.最后我们给出本文的总结讨论及研究展望.  相似文献   

4.
钛酸盐钙钛矿氧化物体系的研究对理解具有铁电极化的功能材料具有非常重要的科学意义.本文对ATiO3(A= Ca,Sr,Ba,Pb,Cd)体系的低温相、结构相变、及其对应的位移模式进行综述.我们着重比较了该体系存在的两类不稳定声子模式,即铁电极化模式(Ferroelectric,FE)和反铁畸变模式(Antiferrodistortive,AFD),在不同体系中所起到的作用.我们举例阐述了晶格失配应变、人工构造超晶格和化学掺杂等方法对这两种模式的调控思路.最后我们给出本文的总结讨论及研究展望.  相似文献   

5.
王永亮  张超  唐鑫  张庆瑜 《物理学报》2006,55(8):4214-4220
采用嵌入原子方法的原子间相互作用势,利用准静态分子动力学模拟研究了Cu原子在Cu(001)表面吸附所导致的基体晶格畸变以及对其附近的另一个吸附原子自扩散行为的影响.研究结果表明,吸附原子的存在可以导致多达10层的Cu基体晶格产生畸变.两个吸附原子所产生的晶格畸变应力场之间的相互作用,可以导致吸附原子运动活性的增加.通过比较同一路径上往返跳跃扩散势垒的差异发现,在原子间相互作用势的有效距离之外,两个吸附原子的扩散行为可以认为是存在晶格畸变应力场相互作用的两个独立吸附原子的扩散;在原子间相互作用势的有效距离之 关键词: 表面吸附原子 晶格畸变 表面二聚体 扩散  相似文献   

6.
李鹏飞  曹海静  郑莉  蒋秀丽 《物理学报》2013,62(15):157501-157501
利用严格对角化方法研究了Thue-Morse准周期调制下 自旋1/2反铁磁XY模型中的晶格畸变行为. 结果显示: 系统中每个格点的晶格畸变幅度介于均匀分布和无序分布之间. 对于较弱的准周期调制, 调制强度的增加有利于晶格畸变的形成. 但是, 对于较强的准周期调制, 调制强度的增加则阻碍晶格畸变的形成. 此外, 系统低能谱的能隙也明显受到准周期调制的影响. 关键词: 晶格畸变 Thue-Morse序列 准周期调制  相似文献   

7.
本文采用对角化三角晶场中d5组态离子的完全能量矩阵的方法,研究了YGaG:Fe3 体系的EPR谱与局域晶格畸变的关系,利用EPR谱的低对称参量D和(a-F)的实验值确定出Fe3 离子在YGaG:Fe3 体系中的键长R=0.2005 nm,键角θ=51.498°,以及晶格畸变角Δθ=0.954°。  相似文献   

8.
利用X射线双晶衍射方法,对从同一Si(111)基片上切割的两块样品,在不同电解电流密度下,腐蚀形成的多孔硅层相对于基体硅的晶格畸变进行了分析。这两块样品晶格的畸变明显不同。其中电流密度较小的样品畸变较大,其多孔硅层对于基体硅在垂直和平行于晶体表面的方向上,晶格有不同程度的膨胀,搁置一段时间后,两者晶格渐渐匹配,但存在着弯曲。两者的(111)晶面取向亦有偏差。电流密度较大时多孔硅层较厚,其双晶反射强度很低,且弥散地迭加在基体硅反射峰上。  相似文献   

9.
蒋德琼  李敏惠  余万伦 《物理学报》1997,46(8):1625-1630
对氟钙钛矿晶体AMF3:Fe3+(A=K,Rb,Cs;M=Zn,Cd)四角对称占位的零场分裂(ZFS)进行分析,证实了晶格缺陷及畸变的存在.对ZFS参量随晶格畸变参量的变化关系进行了详细研究,考虑了缺陷及缺陷引起的晶格畸变两者的贡献,得出几种氟钙钛矿晶体的晶格畸变参量 关键词:  相似文献   

10.
王光军  王芳  沈保根 《物理学报》2005,54(3):1410-1414
通过磁场下热磁曲线的测量,在LaFe114Al16化合物中发现了一个在一定温区内随温度稳定的铁磁相和反铁磁相的共存亚稳态.确定了这个亚稳态能够存在的磁场和温度范围,从而使LaFe114Al16化合物的磁相图更加完善.这个亚稳态的温度稳定性能够很好地解释磁性转变的临界场随温度的变化行为.这个双相共存亚稳态的存在,与LaFe114Al16中的磁性交换作用及晶格畸变所产生的边界相的稳定性有关. 关键词: 共存相 亚稳态 晶格畸变  相似文献   

11.
高温高压条件下,低掺杂的La1-xSrxMnO3化合物发生从菱方相(R3c)到立方相的转变,该相变使其从低温时的绝缘态(极化子有序)转变为金属态.同时,随温度的降低,局域锰离子的自旋也从铁磁长程有序变成了只有短程序结构的自旋玻璃态.这种转变是由于相变引起的Mn—O—Mn键角及Mn—O键长的改变所引起. 关键词:  相似文献   

12.

EPR spectra for ions Ni 2+ (3d 5 ) and Mn 2+ (3d 5 ) substituting Zn 2+ in crystals Zn(BF 4 ) 2 ·6H 2 O are studied within a wide range under hydrostatic pressure in X and Q bands. It is shown that the pressure changes to a considerable extent the spectrum parameters of ion Mn 2+ , reducing axial parameter b_{2}^{0} and increasing cubic one b_{4}^{0} at 9 kbar pressure, there is no temperature dependency of parameter b_{2}^{0} . Hydrostatic pressure changes linearly the initial splitting of ion Ni 2+ and results to a change in D(b_{2}^{0}) sign, which means the spin levels inversion at 3.5 kbar.  相似文献   

13.
Scanned-energy mode photoelectron diffraction (PhD), using the O 1s and V 2p photoemission signals, together with multiple-scattering simulations, have been used to investigate the structure of the V2O3(0 0 0 1) surface. The results support a strongly-relaxed half-metal termination of the bulk, similar to that found in earlier studies of Al2O3(0 0 0 1) and Cr2O3(0 0 0 1) surfaces based on low energy electron and surface X-ray diffraction methods. However, the PhD investigation fails to provide definitive evidence for the presence or absence of surface vanadyl (VO) species associated with atop O atoms on the surface layer of V atoms. Specifically, the best-fit structure does not include these vanadyl species, although an alternative model with similar relaxations but including vanadyl O atoms yields a reliability-factor within the variance of that of the best-fit structure.  相似文献   

14.
Density functional theory has been used to study two of the main topics of oxygen evolution in photosystem II. The first concerns the reduction of the tyrosyl radical that occurs in every S-state transition. The two leading models, hydrogen atom transfer and electron transfer, have been investigated. In the present study, hydrogen atom transfer has the lower barrier. The second topic addressed is O—O bond formation in the S3 to S0 transition, where a Mn3 complex including calcium and chloride cofactors was used as a model. The reaction is suggested to proceed from a bridging oxyl group to a radical hydroxyl, which combines to form the O—O bond with a hydroxide ligand of the Mn complex.  相似文献   

15.
The chemisorption of CH3 on Rh(1 1 1) is studied to understand the origin of the weakened symmetric stretch mode. A few different explanations for this weakened mode have been suggested in previous studies. These include C-H bond depletion and donation into C-H anti-bond orbitals either in an upright or tilted geometry. We investigate these possibilities by performing first-principles density functional calculations. Our results show strong adsorption at all high-symmetry sites with methyl in two possible orientations. A thorough analysis of the adsorption geometry shows that C3v symmetry is preferred over a tilted species, ruling out tilting as a mechanism for C-H mode softening. Evidence of a multi-center bond between methyl and the surface rhodium atoms (similar to the kind shown recently by Michaelides and Hu for methyl on Ni(1 1 1)) is presented, showing that C-H bond depletion is the cause of mode-softening for methyl on Rh(1 1 1). Experimental results have shown that mode-softening diminishes when an electronegative species is coadsorbed, suggesting that donation into C-H anti-bonding orbitals is the mechanism for mode-softening. We therefore examine the coadsorption of oxygen and methyl on Rh(1 1 1). Our results suggest a new model for the effect of O on CH3. Analysis of charge density differences shows that the dominant initial effects of O coadsorption are the removal of charge from the C-surface bond and the transfer of charge to the C-H bond. Subsequent increase of the H-Rh distance further reduces mode softening.  相似文献   

16.
Ferroelectricity driven by Y d0-ness with rehybridization in YMnO3   总被引:1,自引:0,他引:1  
We investigated electronic structure of hexagonal multiferroic YMnO3 using the polarization dependent x-ray absorption spectroscopy (XAS) at O K and Mn L(2,3) edges. The spectra exhibit strong polarization dependence at both edges, reflecting anisotropic Mn 3d orbital occupation. Moreover, the O K edge spectra show that Y 4d states are strongly hybridized with O 2p ones, resulting in large anomalies in Born effective charges on off-centering Y and O ions. These results manifest that the Y d(0)-ness with rehybridization is the driving force for the ferroelectricity, and suggest a new approach to understand the multiferroicity in the hexagonal manganites.  相似文献   

17.
In the present paper, the catalytic role of Ag in the oxygen adsorption of LaMnO3(0 0 1) surface has been theoretically investigated using first-principles calculations based on the density functional theory (DFT) and pseudopotential method. The O2 adsorption energy is larger for the vertical adsorption and the covalent bond was formed between O2 molecule and surface Mn. The calculation of electronic properties of interaction between Ag atom and LaMnO3(0 0 1) surface demonstrates that the most stable position for Ag adsorption is hollow site. The O2 adsorption energy dramatically increased from 0.298 eV to 1.108 eV due to Ag pre-adsorbed. It is Ag pre-adsorbed that facilitates O2 adsorption on surface. The bond length and bond population of O2 molecule indicate that Ag atom facilitates O2 molecule dissociative adsorption. The Ag atom strengthens LaMnO3(0 0 1) substrate activity and activity center was formed on surface, which enhances the electrocatalytic activity of LaMnO3 as solid oxide fuel cells cathode material at low temperature.  相似文献   

18.
谈国太  陈正豪 《物理学报》2007,56(3):1702-1706
通过X射线粉末衍射数据,用Rietveld精修方法分析了Te部分替换LaMnO3中La后,其晶格参数及其结构对称性所发生的变化.结果表明:Te掺杂LaMnO3系列样品具有R3C的晶格结构对称性,其MnO6八面体晶格还产生了伸张畸变,畸变程度随Te掺杂量的增加而增大.此外根据Mn—O—Mn键角、eg电子能带的带宽、A位离子平均半径及A位离子尺寸失配度等的变化特点,推测Te掺杂LaMnO3样品除居里温度等相变物理量将随x增加而非线性变化外,还可能产生自旋玻璃态、相分离等宏观现象. 关键词: 庞磁电阻效应 La-Te-Mn-O X射线衍射 Rietveld精修  相似文献   

19.
采用金刚石压砧高压装置(DAC),对层状钙钛矿结构锰氧化物Ca3Mn2O7的粉末样品进行了高压能散X射线衍射实验。实验结果表明,在0-35GPa压力范围内,Ca3Mn2O7晶体结构发生了两次相变。在1.3GPa左右,由原来的四方相转变为正交相,在9.5GPa左右,又由正交相向新的四方相转变。  相似文献   

20.
The local geometry of OH fragments adsorbed on the Ge(0 0 1)(2 × 1) surface has been examined using O 1s scanned energy mode photoelectron diffraction. These fragments were obtained by the dissociative reaction of the clean surface with H2O. The Ge–O bond length is found to be 1.76 ± 0.02 Å and the Ge–O bond angle to be 15° ± 2° relative to the surface normal. Some information about the positions of the Ge dimer atoms has also been obtained.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号