EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba2Cu3O7-x THIN FILM

We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa₂Cu₃O_7-x(YBCO) thin films 30mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate.     

SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

High quality epitaxial YBa₂Cu₃O_7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO₃, LaAlO₃ and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a J_c (at 77 K, H=0) over 10⁶A/cm². It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa₂Cu₃O_7-x films had excellent superconducting properties and quite perfect structure.     

Study of the optical features of YBa2Cu3O7-x films by SEW spectroscopy

The results of YBa₂Cu₃O_7-x films on SrTiO₃ investigation by far infrared surface electromagnetic waves (SEW) amplitude and phase spectroscopy at temperatures 80–350 K are presented. Strong SEW absorption at frequency 142 cm^–1 has been observed. The origin of the observed absorbtion is proposed to be concerned with slab- phonons in YBa₂Cu₃O_7-x. The optical constants of the films have been obtained. Also has been determined, that only the imaginary part of the SEW refraction index changes when the film transits into superconducting state, while the real part remains unchanged.     

PREPARATION OF a-AXIS ORIENTED YBa2Cu3Ox THIN FILMS

The a-axis oriented YBa₂Cu₃O_x(YBCO) thin films could be grown on (100) SrTiO₃(STO) substrates with STO buffer layers by dc and rf magnetron sputtering either by low-ering the deposition temperature, or by using a self-template technique. For the latter, the resistivity of the thin film at 290K along the substrate [001] direction is about four times larger than that in the [010] direction. The zero resistance temperatures T_c0 are 89 K in both directions. So high quality a-axis oriented YBCO thin films can be prepared by the self-template technique. Also the T_c0 increase monotonously with the reduction of the thickness of the YBCO seed layer.     

Superconducting Transition Temperature and Metal--Semiconductor Transition Temperature in YBa2Cu4O8/La0.67Ca0.33MnO3/YBa2Cu4O8 Trilayer Films

YBa₂Cu₄O₈/La_0.67Ca_0.33MnO₃/YBa₂Cu₄O₈(YBCO/LCMO/YBCO) trilayer films were prepared by magnetron facing-target sputtering. For the first time, the oscillatory behaviour of superconducting transition temperature T_c,ON with the thickness of LCMO (d_L) has been observed. The strongest nonmonotonic information in the T_c,ON--d_L curves appears clearly when d_L is larger than the critical thickness d_L^CR. The metal--semiconductor transition temperature can only be detected at d_L>d_L^CR. The dependence on the ferromagnetic spacer layer in YBCO/LCMO/YBCO systems suggests strongly the interplay of ferromagnetic and superconducting couplings.     

GROWTH MODE OF Cu-RICH PARTICLES ON LASER-ABLATED YBa2Cu3O7 THIN FILMS

The microstructure of the laser-ablated YBa₂Cu₃O₇ (YBCO) thin film deposited on heated (100) SrTiO₃ substrate was examined by transmission electron microscope. The par-ticles on the film mainly consist of CuO and few CuYO₂. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height, A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure.     

LPE growth of PZNT film using superheating YBCO thin film as seed layer

A superheating YBa₂Cu₃O_7-δ (YBCO or Y123) thin film was applied as a seed layer to grow Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT) films by a liquid phase epitaxy (LPE) process. In the present work, the YBCO thin film underwent a growth temperature of 1050 °C, which was about 40 °C higher than its peritectic temperature. It is very interesting that the superheated YBCO seed film could be used to grow not only Nd_1+xBa_2-xCu₃O_7-δ (NBCO) films with similar compositions but also PZNT films with completely different compositions. The XRD analysis confirmed that the PZNT film grown on the YBCO seeded MgO substrate had a good epitaxial relationship of [100](001)_PZNT//[100](001)_YBCO//[100] (001)_MgO. Compared with the PZNT films directly grown on MgO substrates, the LPE PZNT film on YBCO/MgO presented a better surface morphology. It was found that the superheating YBCO seed film plays a crucial role for the LPE growth of PZNT in the process. Furthermore, the superheating mechanism was discussed in terms of thermodynamic theories as well. PACS 77.84.-s; 61.10.Nz; 68.37.Hk; 81.15.Lm; 82.45.Mp     

氧缺位对单相YBa2Cu3O7-x热电势率的影响

研究了氧缺位对单相YBa₂Cu₃O_7-x体系超导电性及热电势率的影响。结果表明,超导转变温度随氧缺位的增加而下降,热电势率随氧缺位的增加而增大。由实验结果推断,单相YBa₂Cu₃O_7-x的多数载流子为空穴。存在较大的声子曳引热电势表明。在YBa₂Cu₃O_7-x超导体中存在较强的电-声子相互作用。 关键词：     

La0.67Ca0.33MnO3薄膜皮秒光电效应

在1064 nm波长脉冲激光（脉宽25 ps）的照射下，钙钛矿氧化物薄膜La0.67Ca0.33MnO3/SrTiO3具有超快光电效应，对激光脉冲显示ps量级的响应时间，上升沿响应时间300 ps，半高宽700 ps，同时，对激光能量的响应灵敏度为500 mV/mJ。     

Effects of tin-compounds addition on Jc and microstructure for YBCO films

Tin-compounds were doped into YBa₂Cu₃O_7−δ (YBCO) films as pinning centers to enhance J_c in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. J_c of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30 nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers.     

Andreev states and the Josephson effect in superconducting heterojunctions on thin YBa2Cu3Ox films

Conductance anomalies at low bias voltages and superconducting currents in Au/YBa₂Cu₃O_x and Nb/Au/YBa₂Cu₃O_x heterojunctions in which the c axis of the YBa₂Cu₃O_x (YBCO) epitaxial film is rotated in the (110) YBCO plane through 11° with respect to the normal to the substrate plane were studied experimentally. The films were prepared by laser deposition onto (7 2 10)-oriented NdGaO₃ substrates. The current-voltage characteristics of the heterojunctions exhibit conductance anomalies at low voltages. The behavior of these anomalies is studied at various temperatures and in various magnetic fields. The critical current and Shapiro steps observed in the current-voltage characteristics of Nb/Au/YBa₂Cu₃O_x were evidence of the Josephson effect in these heterojunctions. The experimental results are analyzed in terms of the model of the arising of bound states caused by Andreev reflection in superconductors with d-type symmetry of the superconducting order parameter.     

YBa2Cu3O6+δ/BaTiO3系复合功能陶瓷特性研究

报道了超导陶瓷ＹＢａ₂Ｃｕ₃Ｏ_6+δ与铁电陶瓷ＢａＴｉＯ₃进行复合的结果。研究了该复合功能陶瓷的物相、（超）导电性和低温电阻温度特性。结果表明，采用合理的合成工艺，可得到呈现混和分布的两相复合功能陶瓷材料；该复合材料的电导特征符合三维渗流导电行为，发现在较高ＹＢａ₂Ｃｕ₃Ｏ_6+δ含量时，样品呈超导电性，并对此作了初步讨论。 关键词：     

A new method to preserve the c-axis growth of thick YBa2Cu3O7–δ films grown by pulsed laser deposition

YBa₂Cu₃O_7–δ (YBCO) films were prepared on (1 0 0) MgO substrates by pulsed laser deposition (PLD) method. In order to eliminate the a-axis growth, which is commonly observed in the YBCO film thicker than a critical value, we developed a new PLD target that was sintered at a temperature far below YBCO 123 phase formation. The surface analysis made by AFM technique confirmed that very fine particles of around 20 nm size could be ejected from the new target to the substrate. The fine oxide clusters could be easily moved and incorporated into the YBCO phase thus benefited the c-axis growth even in the thick films. For instance, only the c-axis growth in the new film with a thickness of about 650 nm was larger than a critical thickness of the a-axis growth. However, in the standard film of the same thickness, there is 24.5% of the a-axis growth accompanying the main c-axis growth. Therefore, the c-axis growth could be preserved in the very thick YBCO film by a non-superconducting target.     

Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：     

DETERMINATION OF THE OXYGEN CONTENT IN YBa2Cu3O7-y FILMS

A method for determination of the oxygen content (y) in YBa₂Cu₃O_7-y films has been established, in which the lattice conetant difference (b-a) of the films was measured and used to fit the function of (b-a) vs y for the experimental data of bulk YBaaCuaO?-y given in the literature. It is suggested that the function of (b-a) vs y can indeed be used in the case of film. In this process the twin structure of the YBa₂Cu₃O_7-y films was used.     

四方和正交YBa2Cu3O7-x体系的输运性质

测量了一系列在不同淬火温度下制得的单相YBa₂Cu₃O_7-x样品的电阻和热电势率。热电势率与温度的关系表明,在正交结构的超导体中,存在声子曳引峰,而在四方结构的样品中,声子曳引峰消失,说明电-声子相互作用对超导电性有影响。根据热电势率数据,估算了样品的费密能和载流子浓度。 关键词：     

Optical study of RE 1 + x Ba 2 - x Cu 3 O 6 (RE = Nd, Sm) aaand YBa 2 Cu 3 O 6 in the mid infrared range

Infrared reflectance, and transmission measurements as well as Raman scattering have been used to study the RE_1+xBa_2-xCu₃O₆ (RE = Nd, Sm) and YBa₂Cu₃O₆ absorption bands in the 1100-1500 cm^-1 infrared range as a function of temperature and beam polarization. In addition to two-phonon absorption between 1100 and 1170 cm^-1, we observe excitations around 1400 cm^-1, occurring in oxygen rich enclosures within the samples, and assign them to an excitation involving two-phonons plus the 270 cm^-1 local mode related to Cu-O broken chains. Thus, the previously reported possible magnetic origin of the 1436 cm^-1 sharp absorption band in YBa₂Cu₃O₆ is contested. Received 14 February 2001 and Received in final form 12 April 2001     

Photoelectron spectroscopic investigation of transformation of trifluoroacetate precursors into superconducting YBa2Cu3O7−δ films

X-ray photoelectron spectroscopy (XPS) has been used to investigate the evolution of surface chemistry of YBa₂Cu₃O_7−δ (Y123) films prepared by the metalorganic deposition (MOD) process using trifluoroacetate (TFA) precursors. Detailed XPS core-level spectra obtained from the samples quenched from various points during the calcining and firing stages have been reported for the first time and are used to identify surface species. The XPS data show evidence of formation of intermediate phases such as Y-O-F, BaF₂, and CuO during the calcining process, which are the decomposition products of yttrium, barium, and copper trifluoroacetates, respectively. The TFA precursors are completely decomposed at the end of calcination. The change of binding energies for Y 3d_5/2, Ba 3d_5/2, and O 1s during the firing process indicates that Y123 starts to form at 800 °C after 0.5 h firing. Based on the experimental results, an alternative mechanism of the chemical evolution from precursor to final film in the TFA-MOD process is proposed.     

YBa2Cu3O7-x涂层导体的外延生长和性能对CeO2缓冲层的依赖性

利用倾斜衬底沉积法在无织构的金属衬底上生长了MgO双轴织构的模板层,在这一模板层上实现了YBa₂Cu₃O_7-x薄膜的外延生长.在外延YBa₂Cu₃O_7-x薄膜前,依次沉积了钇稳定的立方氧化锆和CeO₂作为缓冲层.利用X射线衍射2θ扫描、扫描、Ω扫描和极图分析测定了这些膜的结构和双轴织 关键词： 2Cu₃O_7-x镀膜导体')" href="#">YBa₂Cu₃O_7-x镀膜导体 2缓冲层')" href="#">CeO₂缓冲层 厚度依赖性 外延生长     

Y1-xPrxBa2Cu3O7+δ的红外反射谱

测量了温度范围为4.2—300K的Y_1-xPr_xBa₂Cu₃O_7+δ(x=0,0.1,0.2,0.4,0.5,0.61.0)的红外反射谱,发现在低温下Ba模有双模行为,随着x值增大双模强度反转,在YBa₂Cu₃O_7+δ中已被判定为Y模的位于194cm^-1的反射峰的位置与Pr的含量无关,即用Pr部份或全部替代Y时此峰不发生频移。建议Pr在Y_1-xPr_xBa₂Cu₃O_7+δ,中是正4价,Pr的替代使原来可移动的空穴被定域在Pr的周围,使超导电性受到压制。 关键词：