Development of High Performances and Novel Functions in Low-Growth Temperature (Cu, C) Superconducting Film by Controlling Multi-layer Structure

研究了（Cu，C）-体系[(Cu，C)Ba_2Ca_<n-1>Cu_nO_x:(Cu，C)-12(n-1)n]高温超导体的薄膜工艺及其性能的增强。在CO_2混合气氛下，利用脉冲激光沉积技术在SrTiO_3衬底上成功地合成了（Cu，C）-1201相薄膜。（Cu，C）-1201薄膜具有低生长温度（500~600℃）和超导临界温度（约50 K）的技术优点，足以满足高速数字电路的应用。1201薄膜直接在衬底上的表面粗糙度超过了该相的c轴晶格参数，但通过在1201薄膜和衬底之间插入具有无限层结构的SrCuO_2缓冲液，使表面粗糙度达到了亚纳米水平。（Cu，C）-1201/SrCuO_2结构具有相似的超导性能。这些结果表明，它满足了研究1201及其相关层的多层叠加对其超导性能影响的必要条件。在本研究中，[CaCuO_2/(Cu，C)-1201]×N （N：基本结构的重复数）多层结构的临界温度得到了显著提高。T_<c-onset>和T_<c(ρ=0)>分别达到~100 K和70 K。值得注意的是，这种高t_c试样的生长温度仍然保持在500℃左右。高t_c试样的结构分析表明，异质界面处的应变是超导性增强的主要原因。上述成果表明，利用（Cu，C）-1201层的异质界面效应，研制出了具有高T_c、低生长温度、无有毒元素等技术优点的新型超导膜，这也意味着本研究的目的成功实现。

Thin film process and enhancement of properties of (Cu, C)-system [(Cu,C)Ba_2Ca_<n-1>Cu_nO_x:(Cu,C)-12(n-1)n] high temperature superconductors have been studied. Contrary to the necessity of high temperature and high pressure for fabrication of bulk ceramics of this system, thin films of (Cu,C)-1201 phase have successfully synthesized by utilizing pulsed laser deposition on SrTiO_3 substrate under CO_2 mixed atmosphere. The (Cu,C)-1201 films show technological merits of the low growth temperature of 500～600 ℃ and superconducting critical temperature about 50 K which is sufficient to applications of high-speed digital circuits. Though surface roughness of the 1201 films directly on the substrate exceeded c-axis lattice parameter of this phase, it has been improved up to sub-nano meter level by the insertion of SrCuO_2 buffer with infinite layer structure between the 1201 film and the substrate. The (Cu,C)-1201/SrCuO_2 structures exhibit similar superconducting properties. These results mean that it is satisfied the necessary conditions for the investigation of the effect of multi-stacking of 1201 and related layers on superconducting properties of it. In the present study, remarkable enhancements of critical temperature are achieved in [CaCuO_2/(Cu,C)-1201]×N (N : repetition number of fundamental structure) multi-layered structure. T_<c-onset> and T_<c(ρ=0)> reach～100 K and >70 K, respectively. It is also noteworthy that the growth temperature of such high-T_c specimens still stays around 500℃. Structural analysis of the high-T_c specimens has revealed the strain at their hetero-interfaces is the main origin of the enhancement of superconductivity.The achievements mentioned above shows that the novel superconducting film withtechnological merits : high T_c and low growth temperature, without toxic element has developed by adopting the hetero-interface effect to (Cu,C)-1201 layer, which also means the objective of this research is successfully achieved.