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用全电势线性缀加平面波法(FLAPW)计算了KTa0.5Nb0.5O3四方相和立方相 的光学特性,即介电函数虚部ε2(ω)、光学吸收系数I(ω)和反射率R(ω). 在四方相,介电虚部沿a,b轴,在3,7和23eV附近,分别有三个介电峰.沿c轴的三个介电峰分别位于4,8和23eV.其中4eV附近的介电峰非常尖锐而且高.从8至18eV,沿a,b ,c轴三个方向都有许多低的介电峰.通过对两相光学特性的对比分析发现铁电相KTa0.5Nb0.5O3具有更强的各向异性.
关键词:
平面波法计算
光学常量和参数
铁电体 相似文献
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通过对(1-x)(K0.5Na0.5)NbO3-xSrTiO3(0≤x≤0.15)陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小(x<0.1)时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO3掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相
关键词:
弛豫铁电体
0.5Na0.5)NbO3铁电陶瓷')" href="#">(K0.5Na0.5)NbO3铁电陶瓷
3掺杂')" href="#">SrTiO3掺杂
相变温度 相似文献
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采用基于密度泛函理论的广义梯度近似方法和赝势平面波法,对多铁材料BiFeO3的铁电反铁磁相和可能的高温顺电相的电子结构进行了第一性原理研究.计算验证了BiFeO3基态为G型反铁磁有序,Fe离子的理论磁矩与实验值相符.铁电相变发生后,Bi-6s态和6p态发生了电荷转移,Bi-6s电子的作用更加明显.Born有效电荷的研究表明铁电畸变主要表现为Bi原子的位移,并且电极化强度计算值很好地符合薄膜实验结果.部分态密度的计算表明Bi-6p态的成键轨道与反键轨道间的能量劈裂
关键词:
第一性原理
铁电性
铁电畸变
反铁磁性 相似文献
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采用基于第一性原理密度泛函理论的平面波赝势方法,对0.5NdAlO3-0.5CaTiO3晶体进行结构优化,并对其能带结构,态密度和光学性质进行了理论计算.结构优化后晶格参数与实验数据相符合,误差小于1%;能带计算结果表明0.5NdAlO3-0.5CaTiO3为间接带隙,带隙值为0.52eV;费米面附近的能带由Nd-4f,O-2p,Nd-4p,Al-3p,Ti-4d层的电子态密度确定.同时也计算了该结构的介电函数,反射率和复折射率等光学性质. 相似文献
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溶胶凝胶法制备了Na0.5Bi0.5Ti1-xMnxO3(x=0,0.02,0.04)陶瓷样品,X射线衍射(XRD)分析表明陶瓷样品均形成了单一的钙钛矿(ABO3)型结构且没有杂质相的形成.随着Mn含量的增加,XRD峰向高角度方向移动,表明Mn离子进入Na0.5Bi0.5TiO3晶格.掺杂样品均表现出室温铁磁性和铁电性.磁测量表明样品中存在复杂的磁相互作用,包括铁磁,反铁磁和顺磁相互作用.以上结果表明,通过Mn的掺杂可以使铁电材料Na0.5Bi0.5TiO3转变为多铁材料. 相似文献
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利用能量最小原理, 确定了Ca0.5Sr0.5TiO3晶体中4c位置的Ca/Sr原子对称分布, 建立了Ca0.5Sr0.5TiO3稳定的晶体结构, 在此基础上利用基于密度泛函理论第一性原理的平面波超软赝势方法, 采用局域密度近似和广义梯度近似函数, 计算了Ca0.5Sr0.5TiO3的晶格参数、弹性常数、体弹模量、剪切模量、杨氏模量、泊松比, 并基于Christoffel方程的本征值研究了平面声波的特征, 基于Cahill和Cahill-Pohl模型研究了最小热导率的特征. 计算结果表明: Ca0.5Sr0.5TiO3晶格参数和实验值很接近, 体弹模量大于剪切模量, [100], [010], [001]晶向的杨氏模量、泊松比、普适弹性常数(AU)以及杨氏模量三维图均显示了弹性各向异性; 平面声波在(010), (001)平面呈现各向异性, 在(100)平面呈现各向同性, 平面声波大小与平均横波和平均纵波的数值很接近. Cahill模型最小热导率在各平面呈现各向同性, Cahill-Pohl模型最小热导率在高温时趋于恒定. 准谐德拜模型下Ca0.5Sr0.5TiO3 晶体的摩尔热容和热膨胀系数与CaTiO3晶体的接近, 并且高温下具有稳定的热膨胀性能. 计算所得禁带宽度为2.19 eV, 导带底主要是Ti-3d与O-2p态电子贡献; 由电荷布居和电荷密度图理论证实Ca0.5Sr0.5TiO3具有稳定的Ti-O八面体结构. 相似文献
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《Physics letters. A》2001,288(1):45-48
The full potential linearized augmented plane wave method within the generalized gradient approximation was used to determine the tetragonal fine structure for PbFe0.5Nb0.5O3, i.e., the equilibrium configuration of B-site compound cations (Fe and Nb). It was found that the displacement of atom Fe along [001] direction is 0.022 nm and that of Nb is 0.0020 nm. The ferroelectric instability of complex compound PbFe0.5Nb0.5O3 is mainly coming from the displacement of atom Fe along [001] direction. 相似文献
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The coexistence of cluster glass with long-range antiferromagnetic order in the relaxor ferroelectric PbFe 0.5 Nb 0.5 O3 is elucidated. While the transition at T(N) = 153 K on the infinite antiferromagnetic cluster induces 3m symmetry with large EH2 magnetoelectric response, the disconnected subspace of isolated Fe3+ ions and finite clusters accommodates the cluster glass below T(g) = 10.6 K with field-induced m' symmetry and EH-type magnetoelectric response. Critical slowing-down, memory and rejuvenation after aging, occurrence of a de Almeida-Thouless phase line, and stretched exponential relaxation of remanence corroborate the glass nature. 相似文献
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〗采用磁控溅射技术在Si衬底上沉积Si/\[Fe(10 nm)/Nb(4 nm)/Fe(4 nm)/Nb(4 nm)\]2/ \[Fe(4 nm)/Nb(4 nm)\]4多层膜。 用2 MeV的 Xe离子在室温下辐照多层膜。采用俄歇深度剖析、X射线衍射和振动样品磁强计分析辐照引起的多层膜元素分布、 结构及磁性变化。AES深度剖析谱显示当辐照注量达到1.0×1014 ions/cm2时, 多层膜界面两侧元素开始混合; 当辐照注量达到2.0×1016ions/cm2时, 多层膜层状结构消失, Fe层与Nb层几乎完全混合。XRD谱显示, 当辐照注量达到1.0×1014ions/cm2时, Nb的衍射峰和Fe的各衍射峰的峰位相对于标准卡片向小角方向偏移, 这说明辐照引起Nb基和Fe基FeNb固溶体相的形成;当辐照注量大于1.0×1015 ions/cm2时, 辐照引起非晶相的出现。 VSM测试显示,多层膜的磁性随着结构的变化而变化。 在此实验基础上, 对离子辐照引起界面混合现象的机理进行了探讨。The behavior of the metallic multilayers of Si/\[Fe(10 nm)/Nb(4 nm)/Fe(4 nm)/ Nb(4 nm)\]2/\[Fe(4 nm)/Nb(4 nm)\]4 under 2 MeV Xe ion irradiation has been investigated by depth profile analysis of Auger electron spectroscopy,X ray diffraction and vibrating sample magnetometer. The obtained experimental results show that the inter mixing between Fe and Nb layers occurs in the 1.0×1014 ions/cm2 irradiated multilayer sample which results in the formation of Nb based and Fe based FeNb solid solution. For the samples irradiated to fluence larger than 1.0×1014 ions/cm2, amorphisation is observed, and moreover, the layered structure of the multilayer samples is broken up completely for the samples under 1.0×1016 or 2.0×1016 ions/cm2 irradiation. Vibrating sample magnetometer measurement also reveals that the magnetization of the samples changes with the evolution of the structure of multilayers. Possible mechanism of the modification in Fe/Nb multilayers induced by Xe ion irradiation is briefly discussed. 相似文献
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采用固相反应法制备了SrMn0.5Fe0.5O3陶瓷样品,并对样品的晶体结构,磁性和离子价态进行了系统的表征与分析. X射线衍射谱的Rietveld拟合表明样品属于理想的立方钙钛矿型结构,Mn离子和Fe离子随机占据B位的O八面体中心. X射线光电子能谱表明Mn离子为+3和+4的混合原子价态,Fe离子为+3价. 样品在大于230K的高温区域呈现Curie顺磁特性,在小于230 K的低温区域样品表现出自旋玻璃态行为,这种特性源于Mn离子和Fe离子之间的交换作用及自身价态和分布的不均匀性. 由于Fe3+离子占据O八面体的中心,对顺磁区的Mssbauer谱测量表现为四级分裂.
关键词:
晶体结构
价态
顺磁
自旋玻璃态 相似文献
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Physics of the Solid State - The structure, dielectric characteristics, and magnetoelectric effect of a 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic ceramics are studied. We found that the... 相似文献
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X. Q. Cheng J. Miao S. Z. Wu F. Shao L. Q. Guo X. G. Xu Y. Jiang 《Applied Physics A: Materials Science & Processing》2014,114(2):367-372
Artificial multiferroic superlattices (SL), consisting of BiFeO3 (16 nm)/Bi0.5Na0.5TiO3 (5 nm) (BFO/BNT SL), were grown on (001) SrTiO3 single crystal by pulsed laser deposition method. The cross-sectional, surface morphology, and crystallographic structure of BFO/BNT SL and BFO single layer were investigated. It was found that the electrical, ferroelectric, and magnetic properties of BFO/BNT SL exhibit a remarkably enhancement compared with BFO single layer. The influence of BNT buffering layer, lattice strain, and interfaces interplay of the SL structure are supposed to benefit their ferroelectric and ferromagnetic properties. Our works suggested the BFO/BNT SL with an improved multiferroic characteristics have a promising application for the future informational storage devices. 相似文献
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采用水热方法合成Ce1-x(Fe0.5 La0.5)xO2-δ固溶体.利用X射线衍射技术(X-ray diffraction technique,XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合,通过紫外可见漫反射光谱(UV-Vis diffraction spectrum)及拉曼光谱(Raman spectru... 相似文献
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First-principles study on the structure instability and electronic structure of cubic Ba0.5Sr0.5TiO3
Yuan Xu Wang 《Solid State Communications》2005,135(5):290-293
We present first-principles calculations on the structure instability and the electronic structure properties of cubic Ba0.5Sr0.5TiO3 (BST). The calculated total energy result shows that the Sr ions have a more important effect on the structure instability of BST system than the Ba ions. The off-center displacement of the Sr ions will lower the system energy and makes it instable. In order to understand the interaction between ions, the density of states and the charge density distribution were calculated. From the analysis of the density of states, we conclude that the hybridization between Ba p and O p is stronger than that between Sr p and O p. This is consistent with the analysis of the charge density distribution. 相似文献