LaBa2Cu3-xCoxOy体系中声子振动和自旋关联的研究

我们用X射线衍射,红外光谱以及电子顺磁共振等实验手段,对LaBa2Cu3-xCoxOy (0≤x≤1.0)系列样品进行了研究.研究表明:所有样品皆为单相正交结构.对于不掺杂的样品在535cm-1和585cm-1附近有两个显著的吸收峰,分别相应于Cu(1)-O(1) 和Cu(2)-O(2) 的伸缩振动.在低掺杂区(0≤x≤0.5)535cm-1处的红外峰随x增加向低频方向移动,而585cm-1处的红外峰位置基本不变.当x＞0.5时,这两个峰逐渐宽化,最后变成单个宽峰(x=1.0).掺杂样品在657cm-1处的声子振动模随掺杂量增加向高频方向移动,该峰为Cu(1)-O(4)的伸缩振动模.本文分析了晶体结构和声子振动以及自旋关联变化的相互关系.     

NdBa2Cu3O7-δ/YBa2Cu3O7-δ多层膜体系的外延结构和磁通钉扎的研究

采用脉冲激光沉积技术.在单晶SrTiO3基底上外延生长了一系列名义结构为p×(NdBa2Cu3O7-δ(m)/YBazCu3O7-δ(n))的多层膜和准多层膜(单元层NdBa2Cu3O7-δ较厚而YBa2Cu3O7-δ呈非连贯的岛状分布,m,n为激光脉冲数,p为重复周期).样品的超导转变温度在87-91 K范围,具体大小取决于不同的调制结构,多层膜的重复周期越大,层状界面越多,超导转变温度就越低.磁传输测量表明,准多层的样品不仅具有较高的超导转变温度,而且具有较强的磁通钉扎性能,77 K零场下的临界电流密度高达4×106 A/cm2,显示出良好的应用前景.     

Tc=95K的NdBa2Cu3Ox高温超导外延薄膜的研制

本采用倒筒式直流溅射法原位生长和Ｔｃ值为９５Ｋ的ＮｄＢａ２３Ｃｕ３Ｏｘ外延薄膜，样品的ＸＲＤ分析表明，样品为强烈ｃ轴织构，ｃ轴晶胞参数为１．１７４ｎｍ，样品衍射峰的ＦＷＨＭ＝０．２９°，ＲＢＳ分析表明：薄膜的化学计量为Ｎｄ１．０Ｂａ２．０Ｃｕ３．３Ｏｘ。对影响ＮｄＢａ２Ｃｕ３ＯＸ薄膜Ｔｃ值的因素进行了讨论。     

一维体系的电声子相互作用和声子激发

通过一维金属卤素络合物模型和一维分子晶体模型研究了一维体系的电声子相互作用和声子激发．给出了在绝热近似下重整化的声子色散关系．结果表明：（１）两个模型中电声子相互作用不同，导致前者声频声子重整化可略而后者重整化修正明显；（２）与高分子材料的Ｓｕ-Ｓｃｈｒｉｅｆｅｒ-Ｈｅｅｇｅｒ模型不同，两个模型的声子谱均无能隙 关键词：     

LaBa2Cu3-xZnxOy体系的结构和输运性质研究

我们用固相反应法合成了LaBa2Cu3-xZnxOy（0≤x≤1．0）系列样品．X-光衍射分析显示，在整个掺杂区内皆为正交结构，晶格常数α，b和c随掺杂量的增加略有增大．Zn含量的增加使体系正常态的电阻率上升．红外光谱（限）表明：对于不掺杂的样品，在531cm^-1和583cm^-1附近有两个显著的吸收峰，随掺杂量x的增加前者基本不移动，后者则向高频移动，强度略有减小．电子顺磁共振实验（EPR）揭示了Zn掺杂对Cu^2＋的自旋关联行为的影响．本文讨论了掺杂对结构、输运性质和自旋关联的影响．     

LaBa2Cu3-xZnxOy体系的结构和输运性质研究

我们用固相反应法合成了LaBa2Cu3-xZnxOy(0≤x≤1.0)系列样品.X-光衍射分析显示,在整个掺杂区内皆为正交结构,晶格常数a,b和c随掺杂量的增加略有增大.Zn含量的增加使体系正常态的电阻率上升.红外光谱(IR)表明:对于不掺杂的样品,在531cm-1和583cm-1附近有两个显著的吸收峰,随掺杂量x的增加前者基本不移动,后者则向高频移动,强度略有减小.电子顺磁共振实验(EPR)揭示了Zn掺杂对Cu2 的自旋关联行为的影响.本文讨论了掺杂对结构、输运性质和自旋关联的影响.     

Epitaxial combination of NdBa2Cu3O7−δ /SrTiO3: growth characteristics, structure, and parameters

We have studied the growth characteristics, structure, and parameters of the epitaxial heterostructures (001)NdBa₂Cu₃O_7−δ /(100)SrTiO₃/(001)NdBa₂Cu₃O_7−δ grown by laser ablation on a (100)LaAlO₃ substrate with a thin (∼2 nm) YBa₂Cu₃O_7−δ intermediate layer. The use of an YBa₂Cu₃O_7−δ intermediate layer promotes layered growth of the (200 nm) NdBa₂Cu₃O_7−δ layer, whose free-surface roughness is 4–5 nm. The resistance of the NdBa₂Cu₃O_7−δ layers began to fall off abruptly at T=92 K, and at T≈87 K it vanished completely. The critical current density in the NdBa₂Cu₃O_7−δ layers at T=76 K exceeded 10⁶ cm² A/cm². The dielectric constant of the (400 nm) SrTiO₃ layer sandwiched between the NdBa₂Cu₃O_7−δ epitaxial layers grew by roughly threefold as the temperature was lowered in the interval 300–4.2 K. When a bias voltage of ±2.5V was applied to the NdBa₂Cu₃O_7−δ electrodes, the relative dielectric constant of the (400 nm) SrTiO₃ intermediate layer fell from 1150 to 400 (T=32 K, f=100 kHz). The conductivity of the SrTiO₃ intermediate layer in the direction perpendicular to the substrate plane increased with temperature and the electric field strength. Fiz. Tverd. Tela (St. Petersburg) 41, 395–403 (March 1999)     

结构振动和声辐射的可控性和可观性指标

结构振动和声辐射的可控性和可观性指标对有源控制系统作动器/传感器的布置具有重要意义。对结构振动和声辐射的可控性和可观性指标进行了研究,提出了基于声压输出的振动模态可观性指标,在振动模态可控性和可观性指标的基础上,结合振动模态的声辐射效率,提出了结构声辐射的可控性和可观性指标和基于声压输出的可观性指标。以板结构为例,对结构振动和声辐射的可控性和可观性指标进行了计算分析和讨论,比较了基于声压输出和基于振动响应输出的振动模态可观性,重点研究了基于声压输出的振动模态可观性和结构振动及声辐射的可观性特点,最后对指标值在结构声有源控制中输入(输出)位置选择上的应用进行了讨论和比较,通过数值仿真对指标的有效性进行了验证。     

结构振动和声辐射的可控性和可观性指标

结构振动和声辐射的可控性和可观性指标对有源控制系统作动器/传感器的布置具有重要意义。对结构振动和声辐射的可控性和可观性指标进行了研究,提出了基于声压输出的振动模态可观性指标,在振动模态可控性和可观性指标的基础上,结合振动模态的声辐射效率,提出了结构声辐射的可控性和可观性指标和基于声压输出的可观性指标。以板结构为例,对结构振动和声辐射的可控性和可观性指标进行了计算分析和讨论,比较了基于声压输出和基于振动响应输出的振动模态可观性,重点研究了基于声压输出的振动模态可观性和结构振动及声辐射的可观性特点,最后对指标值在结构声有源控制中输入(输出)位置选择上的应用进行了讨论和比较,通过数值仿真对指标的有效性进行了验证。     

Commensurability oscillations in NdBa2Cu3Oy single crystals

Commensurability between inter-vortex distance and crystal lattice constant is investigated by angular dependent magnetization in very pure twinned and twin-free NdBa₂ Cu₃ O_y single crystals. With increasing temperature the incommensurate states split up and become finally commensurate with half the vortex distance. These new commensurate states are related to a substructure of the intrinsic pinning potential within the unit cell and discussed with respect to temperature, field, anisotropy, and twin structure.     

激子—LO光声子系统

本文采用Huybrechts[1]以及Tokuda[2,3]的拉格朗日乘子法的线性组合算符法,得到了激子的有效哈密顿量和重正化有效质量。用它们计算了激子的结合能,对于电子(空穴)—声子耦合常数大约3的晶体,晶体中激子结合能的计算值与实验值较为接近。     

Partial melting of bulk NdBa2Cu3O7−δ

Il Nuovo Cimento D - Two procedures of partial melting of bulk NdBa2Cu3O7−δ, in air and in reduced oxygen pressure, were developed. When the treatment was carried out in air, poor...     

Pressure-induced superconductivity in tetragonal NdBa2Cu3O6+x

The appearance of superconductivity and relaxation of the transition temperature to its equilibrium value T _c≈30 K over the course of five days have been observed in a tetragonal sample of NdBa₂Cu₃O_6.67 under 1 GPa pressure. The time dependence T _c(t) correlates with a decrease of the room-temperature electrical resistance R(t). The superconducting phase disappears 1.3 h after the pressure is removed. This behavior is explained by a redistribution of charge as a result of pressure-induced oxygen reordering in the CuO_x planes. A large effect of oxygen ordering on the transition temperature under pressure has been observed near the metal-insulator transition (the largest of all those measured in the 1-2-3 system), along with a nonlinear temperature dependence of T _c. Fiz. Tverd. Tela (St. Petersburg) 39, 1328–1334 (August 1997)     

Comparison between the magnetic specific heat of NdBa2Cu3O x and DyBa2Cu3O x

Low temperature heat-capacity measurements have been performed to study the magnetic ordering in NdBa₂Cu₃O _x and DyBa₂Cu₃O _x . In order to investigate the type of ordering, magnetic fields up to 6 T and hydrostatic pressures up to 4.5 kbar were applied. While for NdBa₂Cu₃O _x and DyBa₂Cu₃O _x both the fully oxidized and the fully oxygen reduced samples display long rang antiferromagnetic ordering, only magnetic short range interaction could be found for samples in an intermediate range of oxygen concentration. For NdBa₂Cu₃O _x , where superexchange is believed to be the dominant magnetic interaction,T _N is three times higher in the sample withx=6.26 compared to the one withx=6.98. In contrast,T _N of DyBa₂Cu₃O _x is almost oxygen independent as expected for this mainly dipolar interacting system.