掺杂Y2O3和BaCeO3提高MOD-YBCO超导性能的研究

本文通过在前驱液中添加过量钇盐和铈的有机盐,采用三氟乙酸盐-金属有机沉积法(TFA-MOD) 在铝酸镧单晶基体上制备了含有纳米氧化钇和纳米铈酸钡的YBCO薄膜. 与纯YBCO薄膜相比,掺杂Y₂O₃/BaCeO₃的YBCO膜的临界转变温度几乎保持不变,为91 K左右. 而掺杂Y₂O₃/BaCeO₃的YBCO膜的临界电流密度达到5.0 MA/cm² (77 K, 0T), 是纯YBCO膜临界电流密度的1.5倍.薄膜中的Y₂O₃和BaCeO₃可能在YBCO内部起到了 有效的钉扎磁通作用. 关键词： 钇钡铜氧薄膜 2O₃和纳米BaCeO₃')" href="#">纳米Y₂O₃和纳米BaCeO₃ 磁通钉扎 三氟乙酸盐-金属有机沉积     

TFA-MOD法YBa2Cu3O（7-δ）超导薄膜的交流磁化率研究

通过三氟乙酸盐-金属有机沉积(TFA-MOD)方法在LaAlO3单晶基片上制备了YBa2Cu3O7-δ(YBCO)高温超导薄膜,并测定在垂直于a-b面的外加交变磁场下薄膜样品的交流磁化率随温度的变化关系,在频率543.2 Hz、振幅1 V条件下,样品的超导转变发生在91 K附近.交流磁化率虚部峰值温度Tp随着磁场振幅的变大而向低温区移动,随着频率的增大而向高温区移动,这些现象与磁通蠕动模型相一致,峰值温度TP与外交变磁场的振幅Hac满足Hcaε(1-Tp/Tct)n的关系,其n～1.55;而与频率之间满足1/Tp与lnf的线性关系,可能是由于TAF-MOD薄膜样品中较多孔洞和非位错缺陷的出现使其偏离一般物理气相沉积薄膜样品具有的SNS型连接(n～2).根据频率f与温度T的Arrhenius公式以及二维简约的Bean模型,得到当前薄膜样品的激活能U与电流密度J、以及J与温度T的标度关系.     

TFA-MOD法制备YBCO薄膜生长速率研究

采用原位电阻法对TFA-MOD法高温热处理阶段YBCO薄膜生长速率进行了研究。实验结果和分析表明原位电阻测量法是一种估算YBCO层生长速率的有效方法,不同条件下的测量结果表明薄膜生长速率随管式炉内的温度、水分压、气体流量的上升而明显增加,但随薄膜面积的增加而减小。实验结果为进一步探索和优化热处理过程提供了重要的基础。     

前驱膜形貌对TFA-MOD技术生长YBCO超导薄膜的影响

本文采用三氟乙酸盐-金属有机沉积(TFA-MOD)技术在LaAlO3(00l)单晶基片上、在不同的低温热处理条件下制备出不同形貌的前驱膜.从金相显微镜(OM)和扫描电镜(SEM)观察可以看出,低温预分解时造成前驱膜的形貌不完整性在高温处理后并没有消除.对高温热处理后的YBCO成相膜用X射线衍射进行了物相定性分析,用Jc-Scan Leipzig系统对超导薄膜进行了超导性能分析.结果表明,前驱膜的形貌不完整性造成高温成相阶段样品杂相出现和超导性能降低.经过对低温热处理条件的优化,得到表面形貌完整的前驱膜,避免了高温成相阶段杂相出现,提高了涂层导体的超导性能,Jc可以超过1.5MA/cm2.     

Influence of oxygen pressure on critical current density and magnetic flux pinning structures in YBa2Cu3O7-x fabricated by chemical solution deposition

This paper studies the effect of oxygen partial pressure on the fabrication of YBa 2 Cu 3 O 7 x films on (00l) LaAlO 3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD).As the oxygen partial pressure increases to 1500 Pa,a great increase in the superconducting properties is observed at high magnetic fields parallel to the YBCO c axis.The cross-sectional transmission electron microscope images show that a high density of stacking faults in the size range of 10-15 nm may act as flux pinning centres to enhance the critical current density of the YBCO films     

Trajectory-property relationships in MOD-derived YBCO films

A study of the physical and chemical changes during processing in MOD-derived YBCO films was performed. Fully processed films were 70–85% of theoretical density. The sintering rate increased substantially in the compositional range F/Ba = 1.8–1.5. The activation energy for sintering decreased above a P(H₂O) dependent threshold temperature. XRD indicated this temperature/composition threshold also corresponded to YBCO nucleation, suggesting ex situ YBCO forms in contact with a melt. The ramp rate and P(H₂O) were used to control F/Ba trajectories, which were correlated to performance. The nucleation of YBCO was strongly dependent on processing conditions. Nucleation temperature was varied by at least 60 °C in the study. The optimal YBCO nucleation temperature in the 300–800 nm films was around 725 °C. a-axis grains dominated the microstructures of films where YBCO nucleated at <700 °C. Large second phases, but no a-axis grains, were found when the nucleation temperature was >750 °C.     

Microstructure of YBCO thin films prepared by TFA-MOD method

The microstructure of the recently developed coated conductors was investigated by using electron back scatter diffraction pattern (EBSP). We prepared TFA (trifluoroacetates)-MOD (metal organic deposition) derived YBa₂Cu₃O_7−x (YBCO) films on CeO₂/LaMnO₃/IBAD-MgO/Gd₂Zr₂O₇/Hastelloy C276 substrates of 1 cm-width. The EBSP observation showed that there was a difference of surface microstructure between the midsection and the end of TFA-MOD YBCO film layer in the direction of width. This is attributed not to the local difference of the biaxial texture of CeO₂ top layer but to the local difference of growth condition during TFA-MOD process.     

Precursor evolution and growth mechanism of BTO/YBCO films by TFA–MOD process

In this study, BaTiO3 （BTO）-doped YBCO films are prepared on LaA103 （100） single-crystal substrates by metal- organic decomposition （MOD） using trifluoroacetate （TFA） precursor solutions. The critical current density （Jc） of BTO/YBCO film is as high as 10 MA/cm2 （77 K, 0 T）. The BTO peak is found in the X-ray diffraction （XRD） pattern of a final YBCO superconductivity film. Moreover, a comprehensive study of the precursor evolution is conducted mainly by X-ray analysis and μ-Raman spectroscopy. It is found that the TFA begins to decompose at the beginning of the thermal process, and then further decomposes as temperature increases, and at 700 ℃ BTO nanoparticles begin to appear. It sug- gests that the YBCO film embedded with BTO nanoparticles, whose critical current density （Jc） is enhanced, is successfully prepared by an easily scalable chemical solution deposition technique.     

TFA-MOD方法制备YBCO超导薄膜研究

采用TFA-MOD方法在LaAlO3(001)单晶基片上制备了性能良好的YBCO超导薄膜:临界电流密度(Jc)可达3MA/cm2(77K,0T),超导转变温度Tc≈90K,转变宽度ΔTc=0.5K,其一次涂层厚度达338nm.通过X射线衍射(XRD)分析表明YBCO具有纯c-轴取向、无a-轴取向的晶粒存在.ω扫描分析表明该YBCO薄膜具有很好的面外外延性,其摇摆曲线的半高宽(FWHM)为0.653°. 用SEM分析也表明膜的表面无裂纹存在,表面平整,没有a轴晶粒生长.     

金属有机溶剂法Y1Ba2Cu3O7-δ超导薄膜的Ce掺杂效应

通过三氟乙酸盐-金属有机物沉积方法（TFA-MOD）研究了Ce掺杂对钇钡铜氧（YBCO）超导薄膜性能的影响.观察到10 mol%Ce掺杂使YBCO超导薄膜的c轴取相降低,出现明显的a轴晶粒,薄膜表面变得粗糙.尽管超导临界温度稍有减小,其超导临界电流密度（Jc）在高磁场下性能获得了有效提高,当外磁场强度达到2T时,超导薄...