【作者】 高锋；

【导师】 樊占国；

【作者基本信息】 东北大学 ， 冶金资源与生态环境， 2009， 博士

【摘要】 目前大多数YBCO涂层导体的缓冲层都为绝缘材料,而本实验制备的BaPb03和LaxSr1-xTiO3膜不但具备作为缓冲层的基本条件,并且由于它们具有良好的导电性,也具备了作为涂层导体导电缓冲层的潜力。它们一旦成功地应用于涂层导体当中,将在超导层与金属基底之间架起电流流通的桥梁,在YBCO超导层瞬时电流过载时,起到分流、散热作用,避免YBCO层受到破坏,维护整个带材的稳定性,这样不仅可以显著地增加涂层导体的稳定性,同时也会提高整个涂层导体总的电流密度JE。金属基底不再仅扮演载体的角色,同时也扮演稳定和载流的多重角色,届时,稳定层的厚度将明显减小或完全被去除,涂层导体结构将发生重大改进。本实验选用铅酸钡(BaPbO3)和钛酸锶镧(La1-xSrxTiO3)作为YBCO的导电缓冲层是因为其与YBCO之间具有相似结构、一定的晶格匹配性和良好的化学兼容性。实验采用新型的化学溶液沉积法在单晶LaAl03基底上生长BaPb03和La1-xSrxTiO3薄膜。在制备BaPbO3薄膜的实验中,通过配制不同的前驱液,改变热处理过程中的热处理步骤、烧结温度、升温速率、热处理气氛等因素,最终获得了生成纯净的BaPb03薄膜的最佳参数。结果表明采用“两步法”进行热处理,在氧气或氩气的环境下以10℃/min的升温速率于700℃烧结30 min可以生成连续、致密的有少许(l00)取向的BaPb03薄膜,其室温电阻率为1.0×10-5O.m。在制备Lal_xSrxTi03的实验中,采用了一种新型的前驱液,在氩气气氛下于890℃至990℃之间,均能制备出纯净的La1-xSrxTiO3 (l00)取向的薄膜。为了能够采用全化学溶液沉积法制备YBCO涂层导体,实验以Y、Ba、Cu的乙酸盐为前驱物,以丙酸为溶剂,以吡啶为螯合剂配制了一种新型的YBCO前驱液,以单晶LaAl03为基底,在氩气环境中于830℃至870℃的烧结温度下进行热处理,均能够生成纯c轴取向的YBCO薄膜,薄膜非常纯净,没有其它化学法制备YBCO中常见的BaC03等杂相存在,同时具有连续致密的结构。通过标准四引线法测量830℃烧结的薄膜极限电流密度Jc值为2.4×104A/cm2(77 K,0 T),超导临界转变温度为89 K。在制备YBCO膜热处理过程中,升温速率和氧分压都会对制备的YBCO薄膜结构产生影响,较快的升温速率(72℃/min)可以提高薄膜的晶化程度,但不利于YBCO(001)择优取向的形成。热处理气氛中氧的存在不利于形成纯净的YBCO相,即使采用较小的氧分压(Ar-(0.02%)O2),也会降低YBCO薄膜的纯度。实验中配制了另一种YBCO前驱液,这种前驱液虽然采用的前驱体与第一种前驱液相同,但是前驱液中溶剂性质存在较大差异,有利于在性质不同的隔离层上沉积YBCO层。采用这种前驱液分别在830℃和850℃的热处理条件下制备了纯净的YBCO(00l)取向薄膜,薄膜表面平整光滑。通过对830℃制备的样品超导性能测试,其极限电流密度Jc值为2×104A/cm2。采用这两种YBCO的前驱液在BaPbO3/LaAlO3和La1-xSrxTiO3/LaAl3两种结构上均能生成具有c轴取向的YBCO薄膜,但是由于薄膜中有非(00l)取向的YBCO相以及少量杂相存在,影响了YBCO的超导性能,在液氮温度和零磁场下,极限电流密度Jc值分别为6000为A/cm2和3200 A/cm2。更多还原

【Abstract】 At the present day, most buffer layers in YBCO coated conductors are made from insulated materials, while in this experiment, BaPbO3 and LaxSr1-xTiO3 films not only possess the essential abilities of buffer but also have the potential to be used as conductive buffer layer. And once these conductive buffer layers were used successfully in the structure of coated conductors, they could electrically couple the HTS layer and the underlying metal substrates, especially in the event of a local failure, the superconductor-conductive buffer-metal substrate approach would be to shunt the current through the metallic substrate and maintain electric stabilization by improving the outflow of heat to the surrounding refrigerant bath. The total engineering current density JE would be improved for the whole structure of coated conductors. The metallic substrate no more played the role as body carrier only, but also played the versatile roles as stabilizing and current carrier. At that time, the thickness of stable layer would decrease obviously or be wiped off entirely, and the configuration of coated conductors would experience some important revolution.Because BaPbO3 and La1-xSrxTiO3 having similar configurations with YBCO, can match well in crystal lattice parameters and have good chemical compatibility, they were chosen as conductive buffer layers for YBCO superconductive structure in this experiment. A new chemical solution method was adopted in the experiment to prepare thin films of BaPbO3 and La1-xSrxTiO3 on single crystal LaAlO3 substrates. During the synthesis process, such factors as varied precursors, heat-treated steps, sintered temperature, heating-up rate and the atmosphere were altered constantly to look for the optimal synthesis parameters. Continuous and dense BaPbO3 thin films with some (100) orientation were prepared at sintering temperature of 700℃under Ar or O2 atmosphere using two-step heat treatment process, and the heating-up rate was 10℃/min. The resistivity of these BaPbO3thin films was 1.O×10-5 O·m. Single-phase La1-xSrxTiO3 thin films with obvious (l00) orientation were prepared by depositing a new precursor solution and sintered from 890℃to 990℃under Ar atmosphere.In order to prepare YBCO coated conductors with all-solution method, a new precursor solution with Y、Ba、Cu acetates as precursors and propionic acid as solvent, and pyridine as chelated reagents was deposited on single crystal LaAlO3 substrate and sintered at 830℃to 870℃. As a result, YBCO thin films showed a strong c-axis orientation, which was so pure that no other phase such as BaCO3 phase, which usually was observed in samples prepared by other chemical solution method, was found in them. The thin films were continuous and dense. The limited transient current density Jc of YBCO thin films sintered at 830℃was 2.4 X 104 A/cm2 (77 K,0 T) and the limited transient temperature Tc was 89 K by standard four-point measurement.During the synthesis process of YBCO thin film, both the heating-up rate and the partial pressure of oxygen could affect the structure of YBCO. The fast rate of 72℃/min could boost the thin films crystallization, but (00l) orientation of these thin films was held down at the same time. It was not suitable to prepare pure YBCO phase when there was oxygen existing in the atmosphere of heat treatment because a little oxygen even as 0.02% O2 in Ar could induce non-wanted phase in YBCO thin films.Another precursor solution was prepared in this experiment, and although the solution used the same precursors as the previous one, there was a big difference in solvent properties between these two precursor solutions. These two kinds of solution were propitious to deposit YBCO layers on buffer layers with different properties. Very pure YBCO thin films with a strong c-axis orientation were prepared at the sintering temperature range from 830℃to 850℃with the later precursor solution. The surface of the films was smooth and dense. The limited transient current density Jc of YBCO thin films sintered at 830℃was 2.0×104 A/cm2 (77 K,0 T) by standard four-point measurement.YBCO thin films with c-axis orientation were prepared on the two structures of BaPbO3/LaAlO3 and La1-xSrxTiO3/LaAlO3 respectively with the two kinds of precursors. The superconductive properties of YBCO thin films were affected by the non-superconducting phase in these films. The limited transient current density Jc of YBCO thin films deposited on BaPbO3/LaAlO3 and La1-xSrxTiO3/LaAlO3 and sintered at 830℃was 6000 A/cm2 and 3200 A/cm2 respectively (77 K,0 T) by standard four-point measurement.更多还原