用低温扫描电子显微镜观察 YBaCuO 超导薄膜的临界电流密度 J_c 的分布

利用低温扫描电子显微镜(LTSEM),我们对高温超导 YBaCuO 外延膜的临界电流密度J_c 和临界温度 T_c 的分布进行了观察.低温扫描电镜是目前可以观察超导薄膜中 J_c、T_c 分布情况的仪器,本文详细说明了利用 LTSEM 来观察超导薄膜 J_c、T_c 分布情况的原理,以及如何将 SEM 改装为 LTSEM.实验结果表明 YBaCuO 外延膜表面临界电流密度 J_c 和临界温度 T_c 的分布是不均匀的,但其不均匀性比多晶膜小得多,而且其分布情况与膜的表面形貌有关.     

液氮温区Y-Ba-Cu-O超导薄膜的研究

我们采用了rf磁控反应溅射的方法,在单晶ZrO_2YSZ和多晶SrTiO_3等基片上成功地制备了Y-Ba-Cu-O超导薄膜。所获得的零电阻转变温度达81K。膜厚为1—2μm。 本文对膜的成分、基片、R-T曲线和热处理过程等作了叙述。     

LB膜势垒层高T_c薄膜边缘结的几个实验现象

本文介绍了采用有机分子薄膜 LB 膜(Langmuir-Blodgett)作为势垒层边缘结的制备方法.文中给出了在这种结上所观察到的几种不同的电流-电压曲线,并作了若干讨论.     

高温超导薄膜的一种混刻技术

本文介绍了一种高温超导薄膜表面图形成型的化学湿法刻蚀技术，实验采用饱和乙二胺四乙酸（ＥＤＴＡ）、３％Ｈ３ＰＯ４和饱和ＮＨ４Ｃｌ三种溶液作为腐蚀液，分别对几组ＹＢＣＯ膜样品进行刻蚀，实验中井向腐蚀液和清洗液（去离子水）中通入干燥Ｎ２气．文中给出了测试数据，分析比较了样品刻蚀前后的Ｔｃ，摸索出一种在小尺寸微桥的光刻中对样品超导性能影响最小的化学湿刻技术．     

Y_(1-x)Gd_xBa_2Cu_3O_(6+y)超导单晶的生长与高压氧退火

利用自助熔生长方法制备YBa_2Cu_3O_(6+y),Y_(0.5)Gd_(0.5)Ba_2Cu_3O_(6+y),与GdBa_2Cu_3O_(6+y),超导单晶。经多次试验,选择它的最佳生长条件。将单晶样品置于高压(～150bar)纯氧中退火,结果使T_c达到90K,说明这种退火对增加T_c很有效。劳埃衍射图进一步证明,样品是高质量单晶。关于它的结构、成份分析与磁性亦作过报道。     

YBa2Cu3O7-δ薄膜热激发磁通蠕动研究

本文选择两块零电阻温度分别为82K和71K超导性能不同的薄膜样品,同步进行了电阻在外磁场中展宽的测量,并用Palstra所提出的Arrhenius定律研究两样品热激活能的差别。实验发现样品热激活能随磁场增加线性下降。由测量结果推出的不可逆线仍有B^*-(1-T^*/T_c)^3/2形式。 关键词：     

YBa_2Cu_3O(7-δ)/势垒层/YBa_2Cu_3O_(7-δ)三层结构的制备

本文采用射频磁控溅射法分别以 CeBa_2Cu_3O_(7-δ)和 MgO 为势垒层,原位制备出 YBa_2Cu_3.O_(7-δ)/CeBa_2Cu_3O_(7-δ)/YBa_2Cu_3O_(7-δ)和 YBa_2Cu_3O_(7-δ)/MgO/YBa_2Cu_3O_(7-δ)三层结构.文中给出了一些初步的实验结果,它们表明:在 YBa_2Cu_3O_(7-δ)薄膜与势垒层之间有较严重的互扩散.     

FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS

Magnetic hysteresis loops have been measured for YBa₂Cu₃O_6+x, GdBa₂Cu₃O_6+x and Tl₂Ba₂Ca₂Cu₃O_10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density J_cm has been derived approximately. The field and temperature dependence of J_cm for all samples can be written as: J_cm= J_c0(T)×f(B,T), Where f(B,T) = 1 - Aln(B/B₀(T)), which is similar to the transport critical density strongly affected by flux creep: J_ct = J_c0(B,t)(1 - (k_BT/U₀)ln(BΩd/E_c)). The extraordinary similarity suggests that J_cm is determined not only by flux pinning but also by flux creep. In the first formula, f(B,T) may be correlated with the effect of flux creep on J_cm, and J_c0(T) is determined by flux pinning. J_c0(T) is independent of magnetic field and is proportional to (T_c - T). Similar results have also been found for other samples. It may be the common characteristic of high-T_c superconductors. Magnetic relaxation of YBa₂Cu₃O_6+x and GdBa₂Cu₃O_6+x films has been measured at LN₂ temperature. Using the equation of Hagen et al., effective activation energy U₀ has been deduced, which is about 0.3eV, one order bigger than the value obtained by A = k_BT/U₀. U₀ is almost independent of the field in the field range selected.