用化学溶液法制备银基底Bi-2212超导薄膜

Fabrication of Bi-2212 Thin Film on Silver Substrate by Chemical Solution Method

Bi2Sr2CaCu2Ox(Bi-2212)薄膜制备工艺相对简单,在低温下具有优异的性能,因此备受青睐,已经有不少研究小组采用真空或非真空方法成功制备出高质量的Bi-2212薄膜。一般而言,单晶基底被广泛用于Bi-2212薄膜的制备。与单晶基底不同,银基底无织构,但银基底的表面粗糙度等因素对Bi-2212的c轴织构和临界电流密度有影响。并且由于银基底对Bi系高温超导材料具有较低表面能,因此Bi-2212薄膜可以在银基底上稳定存在。以乙酸-氨水溶液为基础,开发了一种在银基底上制备Bi-2212薄膜的方法,对其中的关键步骤做了详细的研究,主要包括银基底的抛光、化学溶液的配制、烧结温度等。重复旋涂-热解过程可以消除经由一次旋涂热解带来的气泡;另外在银基底和低氧分压条件下,Bi-2212的成相温度点下移,在790℃保温5 h即可制备出单相Bi-2212薄膜。扫描电镜(SEM)观测表明,薄膜表面均匀平整无裂纹。随着烧结温度的升高,Bi-2201相开始出现并且其衍射峰的强度随烧结温度的升高迅速增加;当烧结温度为850℃时,出现了一种棒状相,能谱(EDS)分析表明该棒状相是一种缺Cu相。

The preparation of Bi2Sr2CaCu2Ox（ Bi-2212） thin film was relatively simple and Bi-2212 thin film showed good properties at low temperature,so great attention was focused on this material and many research groups fabricated high quality Bi-2212 thin films by vacuum or non-vacuum methods. In general,single crystal substrates were widely used for the preparation of Bi-2212 thin films.Different from single crystal substrates,the Ag substrates did not show texture,but factors such as the roughness of silver substrates affected the c-axis texture and critical current density of Bi-2212. Moreover,because of the low surface energy of silver substrates for BSCCO high temperature superconductors,it was stable for the growth of Bi-2212 thin film on silver substrate. Based on acetic acidammonia water solution,a method to fabricate Bi-2212 thin film on silver substrate was developed. Critical processes were studied carefully,including the polishing of silver substrates,the preparation of chemical solution,the sintering temperature,and so on. It was found that repeating the spin-coating and pyrolysis processes could eliminate the bubbles produced by one time coating. It was also found that on the Ag substrates and under low oxygen pressure,the sintering temperature for Bi-2212 phase went down. Bi-2212 singlephase thin film could be fabricated by heating at 790 ℃ for 5 h. The smooth surface of Bi-2212 thin film without cracks was shown by scanning electron microscopy（ SEM）. With the increase of sintering temperature,Bi-2201 phase began to emerge,and its diffraction intensity increased fast with the rise of sintering temperature. A rod phase occurred when the sintering temperature was 850 ℃. The result of energy dispersive spectroscopy（ EDS） showed that this rod phase was a Cu-free phase.