慢中子辐照对钇钡铜氧磁通钉扎内耗的影响

一、引言 Brandt等用振动簧片技术研究磁场下非晶超导材料的力学行为时,首先发现:在临界温度以下试样处于混合态时,由于磁通钉扎而使材料的内耗与模量发生剧烈变化.这使得人们有可能用振动簧片技术研究超导体的磁通钉扎过程.高温超导体问世后,Brandt小组及其它研究者用振动簧片技术、高Q振子、扭摆及超声技术等方法对高温超导体的体材料和薄膜材料中的磁通钉扎引起的内耗与模量进行了研究,较系统地测量了振幅、磁场。

Dielectric and Structural Properties of SrTiO_3 Thin Films Grown by Laser Molecular Beam Epitaxy

Here I will review recent progress on the study of dielectric SrTiO3 （STO） thin films. In our work, laser molecular beam epitaxy has been used to prepare multilayer heterostructures consisting of dielectric STO and high temperature superconducting YBa2Cu3Oy （YBCO） thin films for tunable applications. Since the tunability of the dielectric constant and dielectric loss of STO are the key parameters determining the performance of tunable devices and hence the feasibility of this technology, the correlations between the deposition parameters of STO thin films, their structural characteristics, and dielectric properties were studied. An enhanced tunability of 74.7%, comparable to that of STO single-crystal, was observed in our grown STO thin films suitable for tunable YBCO applications. On the other hand, we have grown epitaxial STO （110） films on Si without any buffer layer. The nature of epitaxial growth and interfacial structures of the grown films were examined by various techniques, such as Laue diffraction, high-resolution transmission electron microscopy （HRTEM） and x-ray photoelectron spectroscopy. The in-plane alignments for the STO （110） films grown directly on Si （100） was found as STO//Si and STO//Si . HRTEM study has showed a crystalline transition across the STO/Si interface, indicating it is free from any amorphous oxide layer. We provide clear evidence that the interface mainly consists of Sr silicate phase. The results suggest that such Sr silicate interfacial layer exhibits favourable structural and chemical properties that are particularly useful for epitaxial STO （110） growth on Si. Such STO thin films will be useful for practical applications.

Improvement of epitaxy and crystallinity in YBa_2Cu_3O_y thin films grown on silicon with double buffer of ECO/YSZ

A novel double buffer of Eu2CuO4 (ECO)/YSZ (yttrium-stabilized zirconia) was developed for growing YBa2Cu3Oy (YBCO) thin films on Si substrates. In these films, the severe reaction between Si and YBCO is blocked by the first YSZ layer, whereas, the degradation of crystallinity and superconductivity in the grown YBCO is greatly improved by the second ECO layer. Such an ECO material possesses a very stable 214-T’ structure and excellent compatibilities with YBCO and YSZ. The result shows that the epitaxy and crystallinity of YBCO deposited on Si could be considerably enhanced by using the ECO/YSZ double buffer. The grown films are characterized by high-resolution X-ray diffraction, grazing incidence X-ray reflection, and transmission electron microscopy (TEM), respectively. It is found that well defined interfaces are formed at YBCO/ECO/YSZ boundaries. No immediate layer could be seen. The defect density in all grown layers is kept at a lower level. The YBCO film surface turns out to be very smooth. These films have full superconducting transitions above 88 K and high current carrying capacity at 77 K. The successful growth of highly epitaxial YBCO thin films on silicon with ECO/YSZ buffer, demonstrate the advantages of such a double buffer structure.

YBa_2Cu_3O_y化合物在不同加热温度下的xps测量

测量了正交和正方YBa_2Cu_3O_y化合物的XPS谱线的温度关系。对手超导化合物的Cu2p伴随峰的变化与从氧量确定的Cu原于价的变化相符合。对于非超导化合物,温度升到770K观察XPS谱线中没有明显的变化。Ols的XPS谱线表示氧原子在化合物中的三种不同状态。分析这些峰的温度关系,认为围绕铜的氧构型有三种,即八面体、锥体和正方面。