Melt Processing of YBCO Thick Films Fabricated by Sol Gel Route Powder on YSZ

It is evident that the microstructure and superconducting properties of YBa₂Cu₃O_7−σ (YBCO) thick films are highly dependent upon the route of the precursor. The precursor which was used in the preparation of YBCO thick films was produced using sol gel route technique. The screen printing technique was used in the fabrication of YBCO superconducting thick films on yttria stabilized zirconia (YSZ) substrates. The effect of slow cooling rate and slow cooling window on texturing, microstructure and superconducting properties of the melt processed films was carried out. Optimizing the melt processing program was effective in increasing the molten viscosity, keeping the liquid and hence relatively large grain size that has been obtained. Moreover, grain morphologies like which was found in YBCO bulk materials was observed.     

Preparation and properties of melt-processed thick films of YBCO

A detailed study has been carried out of the successful fabrication of high current capacity, thick films of YBCO on yttria-stabilized zirconia substrates. This has involved the optimization of a number of processing parameters including material composition, processing temperatures and times, ink additives and so on. As a result of this work, thick films have been obtained with thicknesses of as little as 7μ, which are superconducting withT _c=91·5 K and have critical current densities at 77 K of almost 3×10³ Acm⁻². This current decreases rapidly with increasing magnetic field strength, reaching an almost constant value of 100–200 Acm⁻² at 0·4 T.     

Zn^2＋掺杂的YBCO薄膜的超导性能研究

采用溶胶-凝胶法在LaAlO3（LAO）单晶衬底上制备了Zn^2＋掺杂的YBCO薄膜,用X射线衍射（XRD）、高分辨透射电子显微镜（HRTEM）以及标准四引线法分别研究了Zn^2＋掺杂的YBCO薄膜的微观结构、生长取向以及超导性能。结果表明,随Zn2＋掺杂浓度的增大薄膜的临界电流密度提高,而临界转变温度下降、临界转变温区变宽;但当掺杂量〉0.5%（摩尔分数）时,会影响YBCO的c轴取向生长,导致超导性能变差。通过优化掺杂比例后得到Zn2＋掺杂0.5%（摩尔分数）的YBCO薄膜具有最好的综合超导性能,其TC为91.3K,ΔT为1.1K,Jc约为1.54MA/cm^2（77K,0T）。     

大面积YBCO高温超导双面薄膜的生长研究

采用倒筒式直流溅射(ICS)方法,辐射方式加热基片,通过电机带动基片旋转,在两面同时溅射沉积YBCO高温超导双面薄膜。在加热温度为850℃,总压强为35Pa,氧氩比为1∶2,靶基距50mm,基片转速5～40r／min条件下,在20mm×20mm的LaAlO     

Growth and Characterization of YBCO Thin Films by Sequential Deposition and Annealing

A novel thin film growth procedure, sequential deposition and annealing (SDA), which contains the advantages of both in situ and ex situ procedures, was proposed. Y₁Ba₂Cu₃O_{7 – x} (YBCO) high temperature superconducting thin films were grown and characterized by the SDA procedure. Purely c-axis-oriented YBCO thin films with no foreign phases and other oriented grains were successfully prepared. The superconducting transition properties of SDA-grown YBCO thin films were measured by measurement of inductance and resistance. The inductance measurements gave a T _c ^onset of 85 K and a T _c of 5 K. The resistance measurements gave a T _c ^onset of 90 K and a T _c of 5 K. Atomic force microscopy studies showed that SDA-grown YBCO thin films had micrometer-size grains surrounded by many nanometer-size grains. The nanometer-size grains in SDA-grown YBCO thin films are responsible for degradation of superconducting transition properties.     

脉冲激光沉积技术制备超导铌薄膜及其特性研究

采用脉冲激光沉积技术(PLD)在硅衬底上制备超导Nb薄膜,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨X射线光电子能谱(XPS)、综合物性测量系统(PPMS)等测试分析手段,分别考察了不同激光能量、靶基间距、衬底温度对Nb薄膜晶体结构、表面形貌和电学性能的影响。结果表明,Nb薄膜在(110)晶向择优生长,并且随着激光能量的增加,薄膜的结晶质量逐渐提高;合适的衬底温度和靶基间距有利于提高Nb薄膜的结晶性能;在激光能量280 mJ、靶基间距5cm、加热盘温度650℃时制备所得Nb薄膜在(110)晶面半峰宽(FWHM)为0.39°,超导转变温度(Tc)为8.6K,且Nb薄膜具有良好的结晶性能和超导特性。     

Ba源配比对MOCVD法制备YBCO薄膜性能的影响研究

采用单一液相混合源进液及闪蒸的MOCVD系统在LaAlO₃(001)单晶基片上制备YBa₂Cu₃O_7-x(YBCO)薄膜, 研究混合源中Ba含量对YBCO超导薄膜成分、结构及电流承载能力的影响。结果表明, 当Ba含量较小时, YBCO薄膜中易于形成尺寸较小的CuO颗粒; 随着Ba含量的增加, 薄膜中形成Ba₂CuO₃晶粒, 并且Ba₂CuO₃晶粒尺寸随Ba含量的增加而逐渐增大。杂质相的含量、尺寸以及与YBCO的晶格匹配程度对YBCO薄膜的双轴取向生长和电流承载能力具有重要影响。当原料摩尔配比Ba/Y=3.9时, 成功制备出了具有优异面内面外取向、结构致密的YBCO超导薄膜, 77 K下的300 nm厚度薄膜的临界电流密度达到4.0 MA/cm², 该研究结果对于第二代涂层导体的发展具有重要意义。     

定向凝固法制备YBCO超导棒材研究

为了使高温超导体YBa2Cu3O7-d(简称YBCO)的晶粒取向排列,提高其临界电流密度,利用定向凝固方法生长YBCO棒材.采用光学显微镜、扫描电子显微镜研究了定向凝固工艺(抽拉速率和添加211粒子)对YBCO显微组织及片层生长的影响.结果表明,改变抽拉速率可以改善片层质量,211粒子是显微组织及片层厚度的重要影响因素;较低的抽拉速率有利于高质量定向结构的生长;均匀分布的细小Y211粒子会使片层厚度变薄,晶界连通性改善,有利于YBCO的生长.     

衬底温度对掺锆酸钡高温超导YBCO薄膜结构和超导电性能的影响

高温超导氧化物YBCO外延薄膜在掺入少量锆酸钡(BaZrO3,BZO)后,其超导性能会得到较大幅度的提高.研究了不同衬底温度对掺BZO的YBCO薄膜的外延特性及超导性能的影响.以固相反应法制备了YBCO及BZO原材料,利用固相烧结工艺制备了BZO含量为2%(质量分数)的YBCO-BZO复合靶材,采用脉冲激光沉积技术(PLD)在LaAlO3(100)基片上外延生长YBCO薄膜.以不同的衬底温度制备了YBCO薄膜,用X射线衍射和高分辨透射电子显微技术对所制备的YBCO薄膜的外延特性进行了分析.最后比较了在不同衬底温度下制备的YBCO薄膜的超导性能,得到了最佳衬底温度.     

YBCO Superconducting Film Coated on LaAlO3 Substrate by TFA-MOD Process

Epitaxial YBCO film was coated on (001) LaAlO₃ single-crystal substrate by metalorganic deposition of metal trifluoroacetate precursors. From XRD and EDS analysis, it was observed that the film contains CuO or Cu₂BaO₂ segregation, but transport measurement found the segregation structure does not severely prevent the percolation of supercurrent-carrying material. The YBCO films performance is up to 2.4 MA/cm² with I_c of 137 A/cm-width at 77 K and 0 T, and superconducting transition temperature T_c reaches around 91.3 K with sharp transition temperature T_c of 0.36 K.     

TFA-MOD方法制备YBCO超导薄膜生长研究

TFA-MOD方法是制备YBCO涂层导体的最有应用前景的方法之一.本文采用TFA-MOD方法在LaAlO3单晶基片上生长YBCO薄膜并系统地研究了高温退火不同的停留时间对其影响.XRD分析表明退火时间较短时仍有明显的YBCO(00l)取向,但也有其它杂相峰存在,而延长退火时间可以使杂相峰消失而得到纯的且强度更高的YBCO(00l)取向.SEM分析表明未完全结晶的YBCO薄膜表面晶粒大小不一致,而且气孔较多.而结晶良好的YBCO薄膜表面平整致密,空洞较少.随着退火时间的增加YBCO颗粒尺寸在增大.但是,退火时间太长,会有大的空洞,甚至出现裂纹.超导电性能测试表明,随着退火时间的增加超导临界电流(Ic)在增加,但是退火时间达到60min后,Ic即达到最大值,表明60min就能使前驱膜在该实验条件下完全的结晶形成取向良好的YBCO薄膜,YBCO薄膜的生长速度达到0.16nm/s.     

电泳沉积法制备PNN-PZT厚膜的研究

利用电泳沉积法在φ50 μm的铂金丝上制备了厚度约50 μm的0.2Pb(Ni_1/3Nb_2/3)O₃-(0.8-x)PbTiO₃-xPbZrO₃ (PNN-PZT)致密压电陶瓷厚膜. 研究了不同聚合度的分散剂聚乙二醇(PEG)对悬浮液的Zeta电势和厚膜表面形貌的影响.结果显示, 加入高聚合度的分散剂PEG10000所制得的悬浮液比加入低聚合度的分散剂PEG6000制得的悬浮液更稳定, 并且电泳沉积得到的厚膜也更加致密. 本研究解释了不同聚合度的PEG对悬浮液稳定的可能原因, 并比较了连续电泳沉积法与分步电泳沉积法对厚膜表面形貌的影响, 结果表明采用分步电泳沉积法制备的厚膜更加致密. 研究了不同的烧结温度对PNN-PZT厚膜形貌和介电性能的影响, 结果显示烧结温度为1180℃时, 厚膜的介电性能最好, 介电常数达988, 介电损耗为3.7%. 测试了1180℃烧结的PNN-PZT厚膜的电压位移曲线和电滞回线, 结果表明厚膜的有效压电常数为90 pm/V,剩余极化为6.00 kV/cm.     

窄流道式MOCVD制备YGBCO超导层研究

金属有机化学气相沉积能连续、快速的沉积高温超导带材YBa₂Cu₃O_7-x (YBCO) 超导层。但金属有机源的利用率与薄膜沉积速率以及沉积一致性难以兼顾, 制备YBCO高温超导带材的成本居高不下。本文提出了一种新的窄流道式反应室以改进薄膜沉积的一致性。在200 mm长度腔体中沉积的280 nm厚的Y_0.5Gd_0.5Ba₂Cu₃O_7-x薄膜J_c分布在3.2~3.5 MA/cm² (77 K, 0 T), 面外、面内半高宽值分别在1.39°~1.49°和1.88°~2.13°, 表面平整致密。YBCO薄膜良好的一致性表明该窄流道反应室对制备YBa₂Cu₃O_7-x超导带材有好的实用性。     

Preparation and Characterization of Epitaxial-Grown Ba0.65Sr0.35TiO3 Thin Films by the Sol-Gel Process on Pt/MgO Substrates

Epitaxial-grown barium-strontium-titanate (BST, Ba_0.65Sr_0.35TiO₃) thin films have been successfully deposited on Pt/MgO (100) substrates using sol-gel techniques. Crack-free 350-nm-thick films were fabricated using a multilayer spinning technique and calcination at 650°C in oxygen for 1 hr. The X-ray diffraction pattern showed that (001) planes of BST films were mainly laid parallel to Pt (100) and MgO (100). The dielectric constant and dissipation factor for BST thin films at a frequency of 10 kHz were 480 and 0.02, respectively. The results of the temperature-dependence of the dielectric constant and dissipation factor showed that sol-gel–derived BST films had Curie temperatures of about 35°C and diffused ferroelectric phase transition characteristics. The leakage current density through the BST films was about 2.75 × 10^–7 A/cm² at an applied voltage of 3 V. The BST films exhibited a well-saturated ferroelectric hysteresis loop with remnant polarization P _r = 2.8 C/cm² and coercive field E _c = 52 kV/cm.     

低温热处理条件对TFA-MOD方法制备的YBCO薄膜的影响研究

目前，三氟乙酸．金属有机沉积（简称TFA-MOD）方法是制备YBaECU307-6（简称YBCO）涂层导体最有应用前景的方法之一。系统地研究了TFA-MOD过程中低温热处理条件（升温速率和气氛）对在LaAlO3单晶基片上生长的YBCO薄膜的影响。研究结果表明，低温热处理的气氛为纯02时，200～250℃区间的分解速度不能太快，否则YBCO薄膜就不均匀和致密，薄膜中会出现较多的孔洞，薄膜的面外取向性也较差，从而影响薄膜的超导性能，然而过慢的分解速度也会使薄膜表面有较大的CuO析出物。分解速度为0．08℃／min时才可以得到结构和超导性能良好的YBCO薄膜。同时研究也发现在低温热处理过程中如果采用Ar和2．5％O2混合气氛则可以减弱三氟乙酸盐分解的剧烈程度，从而使低温热处理的分解速度提高到0．8℃／min，得到的YBCO薄膜同样具有较好的面外取向性和超导性能。     

Study of the Usual and the Unusual Effect of a DC Magnetic Field on the Microwave Properties of Different Superconducting YBCO Thin Films

An experimental observation of the improvement of the microwave properties of high temperature superconductor thin film subjected to a weak DC magnetic field is reported. This characterization was done with two YBCO films deposited onto LaAlO₃ substrates and the coplanar resonator technique was used to extract their microwave properties. The results are presented as a comparison between the behaviors of a sample that exhibits an unusual effect with another sample that has a usual behavior. To understand the origins of such a difference, the crystallographic properties and the microstructure were investigated respectively by mean of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). A major difference in terms of growth axis orientation and of granularity has been observed between the two samples. Based on the correlated variation of the surface resistance and the surface reactance of the considered sample, the presence of anomalous weak links and also of a-axis grains in one of the films could explain its unusual behavior.     

Effect of Substrates on Superconducting Properties of MgB2 Thick Films Fabricated by Spraying Method

MgB₂ thick films have been prepared on Al₂O₃, MgO and SrTiO₃ ceramic substrates using the spray method with two different heat-treatment cycles, 925???C with 10?min (Group?A) and 610???C with 24?h (Group?B). The structural/microstructural (XRD, SEM) and transport (R?CT, MR?CT) properties of the films prepared were investigated. XRD analysis showed that the films in Groups?A and?B consisted mainly of MgB₂, but the peaks originating from the substrates were also observed in films fabricated on the Al₂O₃ substrate. From scanning electron microscopy, it was seen that the surface of MgB₂ thick films prepared is not sufficiently homogeneous. Some cracks and heaps with different sizes were observed. The best electrical results were obtained for films in Group?A on Al₂O₃ substrate. The T _c value for films in Group?A was found to be 36.1?K, 36?K and 35?K, for Al₂O₃, MgO and SrTiO₃ substrates, respectively. No superconducting state was reached for films in Group?B on the SrTiO₃ substrate. In all the films which showed a superconducting state, the magnetic field strongly affected T _c . A?tail in the resistance curves was observed with increasing magnetic field for films in Group?A on the MgO and SrTiO₃ substrates. At magnetic fields above 1?T for films in Group?A on the SrTiO₃ substrate and above 2?T for films in Group?A on the MgO substrate, the zero-resistance temperature, T ₀, was not obtained.     

氩离子刻蚀对TFA-MOD法YBa2Cu3O7-x薄膜性能的影响研究

TFA-MOD工艺制备的YBa₂Cu₃O_7-x(YBCO)薄膜有独特的生长机制, 高温晶化后的YBCO薄膜表面存在一层由Ba-Cu-O异质相及a轴生长的YBCO晶粒组成的杂质层。为了满足零电阻超导焊接和超导带材钎焊搭接的研究需要, 在不破坏超导特性和晶体结构的前提下, 采用Ar离子对TFA-MOD工艺制备的YBCO薄膜进行刻蚀, 对薄膜进行纳米级的减薄, 实现对薄膜表面杂质的去除。利用拉曼光谱、扫描电子显微镜和X射线衍射等方法对不同刻蚀时间下的薄膜状态进行表征。结果表明, 1.3 μm厚的YBCO薄膜表面杂质层厚度约为220 nm, 并且在过度刻蚀的情况下, YBCO薄膜仍然是c轴取向, 晶体结构没有被破坏。刻蚀后,薄膜内部氧空位缺陷的产生会造成超导转变及载流性能的降低, 但通过吸氧处理后薄膜性能可恢复。     

Fabrication of Superconducting MgB2 Thin Films by Magnetron co-Sputtering on (001) MgO Substrates

We fabricated superconducting MgB₂ thin films on (001) MgO substrates by magnetron rf and dc co-sputtering on heated substrates. We annealed the samples ex-situ and in-situ at temperatures between 450 ^°C and 750 ^°C. The substrate temperature during the sputtering process and the post annealing temperatures play a crucial role in forming MgB₂ superconducting thin films. We achieved a critical onset temperature of up to 27.1 K for the ex-situ and 25.6 K for the in-situ annealed samples at a film thickness of 30 nm. The samples shows an out of plane (0002)-Peak which was determined by x-ray diffraction.