Fe掺杂YBCO体系结构变化与团簇效应的正电子实验研究

用固态反应法制备了YBa₂Cu_3-xFe_xO_y(x=0—0.5)一系列样品,反应在空气中进行.运用正电子湮没技术、扫描电子显微镜和X射线衍射进行了研究,并测定了氧含量.正电子湮没结果发现,x=0.12时短寿命分量τ₁和长寿命分量τ₂都存在一异常变化.X射线衍射和扫描电子显微镜研究分别表明,材料在x=0.12—0.15区间内发生正交四方相变,晶粒尺寸突然由小变大.通过对上述实验结果的分析可以得到,在该类材料中,正电子对结构相变十分敏感;另外,当Fe掺杂量增大到一定程度时,Fe原子由随机分布变为成簇分布 关键词： Fe掺杂YBCO 高温超导电性 正电子湮没 结构相变

POSITRON ANNIHILATION STUDY OF THE STRUCTUREAND CLUSTERS IN Fe-DOPED YBCO

A series of YBa2Cu3-xFexOy(x=0—0.5)samples were prepared in air by the standard solid-state-reaction method.The crystal structures and physical properties have been studied by means of positron annihilation technology (PAT), scan electronic microscope (SEM) and X-ray diffraction (XRD).Oxygen contents of the samples were determined by a volumetric method.The results of PAT show that the short lifetime component τ1 and long lifetime component τ2 are all changed anomalously between x=0.12 and 0.15 where the compounds undergo the orthorhombic-tetragonal (O-T) phase transition.In addition,the grain size of the sample with x=0.15 is much larger than that of samples with x<0.15.Based on the experimental results,we obtain the following conclusions.The positron can be used as a sensitive probe for O-T phase transition in this system.When x>0.15,the doped Fe atoms and incoming oxygens tend to associate into clusters rather than to randomly distribute over the crystal lattice.The cluster behavior is in agreement with the results of theory and other experimental results.