过量La掺杂的Bi—2201单晶的超导电性

在极度Ｌａ掺杂的Ｂｉ２Ｓｒ２－ｘＬａｘＣｕＯ６＋ｙ单晶中发现Ｔｃ高达３６Ｋ的超导相。Ｘ射线衍射（ＸＲＤ图和劳埃斑点实验都显示单晶具有很好的质量。ＥＤＸ分析结果和由ＸＲＤ得到的单晶ｃ轴长度均证实单晶处于极度Ｌａ掺杂的区域。一般来说，处于如此高Ｌａ掺杂区域的Ｂｉ－２２０１体系不表现出超导电性。因为我们的样品曾在Ｏ２中６８０℃退火１０小时，而且极度Ｌａ掺杂会导致长程反铁磁有序背景。所以我们将这种高Ｔｃ的     

La掺杂Bi-2201单晶中宏观相分离迹象的发现及研究

在对系列Ｌａ 掺杂的Ｂｉ２Ｓｒ２ － ｘＬａｘＣｕＯ６ ＋ δ单晶的研究中,我们发现在极度Ｌａ 掺杂（ 空穴极度欠掺杂） 的样品中有高达３６Ｋ 的超导相出现．Ｘ 射线衍射图（ＸＲＤ） 和电镜照片都表明这种极度空穴欠掺的样品有很好的单相性,从而排除了样品化学不纯的可能．另外,对这种样品进行脱氧处理后,此超导电性相应消失,说明了这种高Ｔｃ 的超导电性是由活动性空穴掺杂引起的．虽然对相应样品在正常态的磁测量没有测出反铁磁峰（Ｎｅｅｌ 峰） ,但对系列样品的拉曼散射研究发现样品随着Ｌａ 含量的增多,其反铁磁交换作用明显加强．所以,我们认为这种高Ｔｃ 超导电性的出现是在Ｂｉ２２０１ 体系中存在宏观相分离的明显迹象     

不同气氛退火对PbWO4单晶发光的影响

通过对不同气氛条件下退火的PbWO4(PWO)单晶样品的激发谱与发射谱的对双研究，发现真空退火从整体上抑制PbWO4的发光强度，氧空位（Vo）缺陷是420nm吸收和红光发射的原因，而空气退火可以有效抑制Vo缺陷，全面改善PWO的发光性能。另外，首次报道了310nm附近的激子激发峰发生劈裂的现象，其中波长较长的320nm激发对应于与Vo缺陷相关的激子激发态。     

Pb、La掺杂Bi2201相高质量单晶的生长和表征

自助熔法从富Ｂｉ２Ｏ３ 的Ｂｉ１ ．８ ＋ ｘＰｂ０ ．２Ｓｒ１ ．６５Ｌａ０ ．３５ＣｕＯｙ（ｘ＝ ０ ．１ ,０ ．２,０ ．３ ,０．４ ,０ ．５） 熔体中生长出了高质量的Ｐｂ、Ｌａ 掺杂的Ｂｉ２２０１ 相大单晶,最大尺寸达８ ×４ ×０ ．０５ｍｍ３ ．在生长单晶时不同程度过量的Ｂｉ２Ｏ３ 用作助熔剂,最佳助熔剂含量以及最佳温度控制过程被确定．通过单晶的（００ｌ） ＸＲａｙ 衍射和摇摆曲线以及电子衍射对一块尺寸为４ ×１ ．６ ×０ ．０３ｍｍ３ 的高质量单晶做了结构表征．由试验发现从富Ｂｉ２Ｏ３ 的熔体中生长高质量Ｂｉ２２０１ 相大单晶的关键是合适的助熔剂含量和温度控制过程     

孔洞和空位对单晶铝力学性能影响的分子动力学研究

采用分子动力学方法模拟含孔洞的单晶铝单轴拉伸过程,研究晶向、孔洞体积分数、空位体积分数等对孔洞生长的影响.结果表明：对于不同的晶向,决定孔洞生长变形的微观机制不同.[010]晶向单轴拉伸情况下,形变机制主要是｛111｝面位错引起的堆垛层错;[111]晶向单轴拉伸情况下,形变机制主要是位错的移动、堆积与发射.此外,孔洞及空位的体积分数对[010]、[111]晶向的孔洞生长过程也有着明显的影响.总的来说,随着孔洞或者空位体积分数的增加,材料的杨氏模量变小,屈服强度、屈服应变下降.     

La2-xBaxCuO4单晶反常的正常态输运性质研究

测量了La2-xBaxCuO4系列单晶样品的电阻率和热电势,我们发现,当＝0．125（x＝1／8）时,La2-xBaxCuO4的截流子是所有样品中局域化最强的,但数据分析结果显示,它又是弱域化行为,文中我们讨论了Tc的被压制的原因,得出这可能与低温下LTO到LTT的结构相变,空穴与自旋的静态条纹有序有关,热电势结果观察不到任何声子曳引的痕迹,表明在LBCO体系中电声子的相互作用很弱。     

La2-xSrxCuO4单晶的平面内磁阻研究

测量了三种不同组分La2-xSrxCuO4(x＝0.09,0.18,0.24)单晶的平面内横向(H∥c,J∥ab)和纵向(H∥J∥ab)磁阻,发现平面横向与纵向磁阻都是正的,并且纵向磁阻与横向磁阻相比较很小,表明横向磁阻的主要贡献是电子轨道部分,也反映了ab面内和c方向电子有效质量的各向异性.三种成分单晶样品的平面内横向磁阻在不同温度随Sr含量x的变化显示在最佳掺杂浓度附近平面横向磁阻最大.     

氧空位对钴掺杂氧化锌半导体磁性能的影响

从实验和理论上阐述了氧空位对Co掺杂ZnO半导体磁性能的影响.采用磁控溅射法在不同的氧分压下制备了Zn_095Co_005O薄膜,研究了氧分压对薄膜磁性能的影响.实验结果表明,高真空条件下制备的Zn_095Co_005O薄膜具有室温铁磁性,提高氧分压后制备的薄膜铁磁性逐渐消失.第一性原理计算表明,在Co掺杂ZnO体系中引入氧空位有利于降低铁磁态的能量,铁磁态的稳定性与氧空位和Co之间的距离密切相关. 关键词： Co掺杂ZnO 稀磁半导体 第一性原理计算 氧空位缺陷     

利用扫描隧道谱(STS)对石墨单晶表面局域电子态的研究

利用ＳＴＳ测量并结合扫描隧道显微镜（ＳＴＭ）扫描图象，给出一组沿石墨单晶表面原子分辨的ＳＴＭ图象上某一线段各点处的扫描隧道谱．ｄ（lｎI）／ｄ（lｎＶ）～ｅＶ由测量谱给出的样品表面Ｅ_Ｆ附近局域态密度分布与由体能带结构计算得到的结果在一定程度上相符合，将各条曲线中Ｅ_Ｆ附近的态密度峰能量对相应的空间位置作图，给出石墨表面E_F附近能态密度在测量区域内实空间的变化。通过对表面不等价Ａ，Ｂ类原子处局域电子结构的分析并利用简单模型进行计算，给出了与实验 关键词：     

PbWO4晶体空位型缺陷电子结构的研究

采用基于密度泛函理论的相对论性离散变分和嵌入团簇方法计算了PbWO4晶体中与氧空位和铅空位相关缺陷的态密度分布,并运用过渡态方法计算了其激发能. 结果表明:PbWO4晶体中WO3+VO缺陷的O2p→W5d跃迁可引起350nm和420nm附近的吸收,并且发现VPb的存在可以使WO42-基团的禁带宽度明显变小.     

Water as a source for oxygen incorporation into acceptor doped SrTiO3 single crystals

The possibility of the incorporation of oxygen and deuteron stemming from the dissociation of water into iron doped strontium titanate single crystals with two different iron concentrations (0.13 and 0.013 at.% Fe) has been investigated. Double labeled water (²H₂¹⁸O) was used for Isotope Exchange Depth Profiling. It acts as an incorporation source of ¹⁸O into Fe-doped SrTiO₃(100) single crystals. Total dissociation of the water takes place in the vicinity of the SrTiO₃ surface and both oxygen and deuteron incorporate into the SrTiO₃. The results of the diffusion profile evaluation confirm that oxygen and deuteron migrate independently in the bulk. Oxygen incorporates into the material at high incorporation rates, practically comparable with the ones resulting from an O₂ atmosphere. The interaction of H₂O with SrTiO₃(100) surfaces was further studied with Metastable Induced Electron Spectroscopy and Ultraviolet Photoelectron Spectroscopy. Neither partial dissociation of water molecules nor any significant formation of surface OD groups was observed.     

Interpretation of charge transfer bands in Fe doped SrTiO3 crystals

The electronic structures of SrTiO₃ crystals doped with Fe³⁺, Fe⁴⁺ and Fe⁵⁺ ions have been investigated using the Xα cluster approach. The ground-state eigenvalues show the lower Fe acceptor level, of t_2g↓ symmetry, localized inside the SrTiO₃ band gap, respectively at 2.8 eV $\text{(}\text{Fe}{}^{\mathrm{3+}}\text{, S =}\text{5}\text{2}\text{), 1.6}\text{eV}\text{(}\text{Fe}{}^{\mathrm{4+}}\text{, S = 1)}\text{or}\text{1.1}\text{eV}\text{(}\text{Fe}{}^{\mathrm{4+}}\text{, S = 0)}\text{and}\text{1.1}\text{eV}\text{(}\text{Fe}{}^{\mathrm{5+}}\text{, S =}\text{3}\text{2}\text{)}$ above the valence band edge. Other acceptor levels, with eg↓ and eg↑ symmetries, appear inside the gap when the Fe nominal ionicity increases.The theoretical Xα excitation energies of O 2p-Fe 3d transitions confirms the experimental interpretations of acceptor charge transfer bands for the optical absorption spectra of SrTiO₃:Fe⁴⁺ and SrTiO₃:Fe⁵⁺ crystals.The large optical excitation energies compared with the thermal transitions are partly due to the O 2p band width.     

The influence of interfacial barrier engineering on the resistance switching of In2O3：SnO2/TiO2/In2O3：SnO2 device

The I-V characteristics of In2O3：SnO2/TiO2/In2O3：SnO2 junctions with different interracial barriers are inves- tigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interracial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interracial barrier engineering, could be exploited for novel applications in nonvolatile memory devices.     

Defects in Nd2CuO4 and Nd1.815Ce0.185CuO4 single crystals

We describe here four kinds of defects found in Nd₂CuO₄ and Nd_1.815Ce_0.185CuO₄ single crystals grown by the traveling solvent floating zone method. These defects include: (1) cracks, (2) inclusions, (3) gas bubbles and (4) uneven distribution of Ce⁴⁺. The formation mechanism of these defects and the measures of eliminating these defects are discussed. It is thought that the preparation of raw materials and stringent growth conditions are necessary to obtain high quality of Nd₂CuO₄ and Nd_1.815Ce_0.185CuO₄ single crystals.     

LaAlO_3/SrTiO_3界面增强光伏效应

探索LaAlO_3/SrTiO_3(LAO/STO)界面产生的新奇物理特性对理解关联电子系统中多自由度耦合和设计功能材料器件具有重要的价值.本文通过脉冲激光沉积方法在SrTiO_3基底上制备了LAO/STO薄膜,研究了正面照射LAO/STO膜面和侧面照射LAO/STO界面时的光伏效应,探讨了LAO/STO界面对光伏效应的影响.研究结果表明,在同样光照能量下侧面照射LAO/STO界面产生的光电压远高于正面照射LAO/STO膜面产生的光电压,说明LAO/STO界面对光伏效应有明显的增强作用.通过偏压调控可以进一步增强照射LAO/STO界面产生的光电压,当偏压为60 V时, LAO/STO样品的位置探测灵敏度达到了36.8 mV/mm.这些研究结果为设计场调控位置敏感探测器等新型光电子器件提供了新的思路.     

Surface characterization of In4Se3 single crystals

Surface properties of indium subselenide (In₄Se₃) were studied. It was confirmed, that the superstructure of this crystal is characterized by nanowire-like cylindrical clusters with diameter dimensions of about 20 nm and stairs along the a-axis up to 5 nm, depending on the cleavage conditions.     

掺铑BaTiO3单晶场致应变特性的研究

系统地研究了掺铑的BaTiO₃单晶在老化后的场致应变性能.研究发现，晶体的场 致应变随老化时间的增加而增大，在老化27天后，在300V/mm的电场下，其双向场致应变可达1.11％；在较小的测试频率下（0.01Hz）也可得到0.95％的可逆的巨大的单向场致应变，在低频范围内，晶体的单向场致应变随测试频率增大而减小；研究晶体老化后的电滞回线，发现其 形状类似于蜂腰磁滞回线.实验结果表明，对BaTiO₃单晶掺杂铑元素可以大大改 善其电致伸缩性能，可能产生新的在超大应变及非线性驱动器中的应用. 关键词： 3单晶')" href="#">BaTiO₃单晶 掺铑 场致应变 老化     

Ultraviolet laser-induced photovoltaic effects in miscut ferroelectric LiNbO3 single crystals

This paper investigates the photovoltaic properties of miscut LiNbO 3 single crystal with different thicknesses under irradiation of a 248 nm ultraviolet laser pulse with 20 ns duration without an applied bias.Nanosecond photovoltaic response is observed and faster rise time is obtained in thinner samples.In accord with the 248 nm laser duration,the full width at half maximum of the photovoltaic signals keeps a constant of ～ 20 ns.With decrease of the crystal thickness,the photovoltaic sensitivity was improved rapidly at first and then decreased,and the maximum photovoltage occurred at 0.38 mm-thick single crystal.The present results demonstrate that decreasing the LiNbO3 single crystal thickness can obtain faster response time and improve the photovoltaic sensitivity.     

掺Bi钨酸镉单晶体发光特性的研究

用坩埚下降法(Bridgman)生长出了Bi离子掺杂的CdWO₄单晶.测定了晶体不同部位的吸收光谱、发射光谱和X射线电子能谱(XPS).Bi离子的掺入引起CdWO₄晶体的吸收边从345 nm红移到399 nm.在311 nm, 373 nm,808 nm和980 nm光的激发下,分别观测到中心波长为470 nm,528 nm,1078 nm和较弱的1504 nm四个不同发射带.Bi:CdWO₄单晶的XPS谱分别与Bi₂ 关键词： Bi离子 荧光光谱 X射线电子能谱 4单晶')" href="#">CdWO₄单晶     

Theoretica Study on defects associated with lead vacancies in PbWO4 crystals

The defects associated with lead vacancies(VPd)in lead tungstate crystals(PbWO4) are investigated by the relativistic self-consistent discrete variational embedded cluster method.We focus on the density of states and the effect of Vpb on surroundings,the results show that the existence of Vpb can diminish the bandwidth of WOr^2- group,however,it can neither produce O^- and Pb^3 ions nor result in absorptions at 350 and 420nm,The charge balance of VPb may be evenly compensated by the surrounding oxygen ions.