基于YBCO/STO的频率电调特性研究

对铁电材料SrTiO3(STO)薄膜的介电性质及其在微波器件特别是高温超导滤波器频率调节方面的应用进行了研究.在相关理论分析和软件仿真计的基础上的计算,获得了电调微带线谐振器的频率调节范围等电特性与器件结构参数的关系.我们采用YBCO作为STO薄膜的驱动电极,使用脉冲激光沉积的方法制备了叉指结构的电调薄膜.利用微波近场显微镜测量了电场对STO薄膜的介电性质的影响.     

Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr0.4Ti0.6)O3 nanotubes

We report the effects of adsorbates on the Raman spectra of Pb(Zr_0.4Ti_0.6)O₃ nanotubes (PZT-NTs). PZT-NTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. This background can be suppressed by adjusting the Raman excitation wavelength from 514.5 nm to 414.6 nm. It can also be removed by post-annealing the PZT-NTs at 500 °C, but it returns readily after re-exposure to air. X-ray photoelectron and Fourier transform infrared spectroscopies show that hydroxyl and carbonate groups are adsorbed onto the surfaces of the PZT-NTs during exposure to air. Moreover, dispersive Raman spectra reveal that the background is a tail of a very broad band from 1000 to 4000 cm^?1, which corresponds to hydroxyl groups. These results suggest that the main contribution to the Raman background of the PZT-NTs is that of surface hydroxyl groups rather than carbonate groups.     

EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba2Cu3O7-x THIN FILM

We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa₂Cu₃O_7-x(YBCO) thin films 30mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate.     

SUPERCONDUCTING PROPERTIES AND STRUCTURAL PERFECTION OF EPITAXIAL YBa2Cu3O7-x THIN FILMS

High quality epitaxial YBa₂Cu₃O_7-x thin films have been succcessfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO₃, LaAlO₃ and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a J_c (at 77 K, H=0) over 10⁶A/cm². It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by X-ray diffraction. Rutherford backscattering and channeling spectroscopy, X-ray double-crystal diffraction and transmission election microscopy. The experimental results demonstrated that the epitaxial YBa₂Cu₃O_7-x films had excellent superconducting properties and quite perfect structure.     

喷雾沉积热分解法在SrTiO3和织构的Ag基底上制备YBa2Cu3O7-x涂层超导膜

本文研究了用喷雾沉积热分解法在(110)Ag单晶、{110}<011>Ag带、(100)SrTiO3三种不同的基底上制备YBa2Cu3O7-x涂层超导薄膜.通过对溶液成份,载气流量,沉积温度,退火时间等条件的系统研究,我们发现上述参数与薄膜的成份,表面形貌,织构以及超导性能有密切的关系.在Ag单晶基底上所获的YBCO薄膜具有很强的平面双轴织构,起始转变温度达到了90K,Jc值超过了104A/cm2(77K,0T);改进试验装置后,以织构Ag为基底,制备出了15cm长的YBCO超导带材,Jc值达到了104A/cm2(77K,0T).同时,我们发现温度梯度在热分解区间内对薄膜的形成起到了重要的作用.随后我们又在喷雾加热系统中附加一个金属加热圆筒,以改善加热区间的温度梯度,薄膜的性能得到了明显的提高.在(100)SrTiO3上的YBa2Cu3O7-x薄膜,(102)极图的FWHM值达到了0.70°,薄膜的起始超导转变温度为91K(ΔTc=1.5K),Jc值接近105A/cm2.