Cao Shixun

Experimental study of the pre-crystallization process in the amorphous fast ionic conductor 0.60AgI0.25Ag2O0.15P2O5

Abstract Systematic investigations on the pre-crystallization process in the amorphous ionic conductor 0.60AgI0.25Ag 2 O0.15P 2 O 5 have been carried out by means of ultrasonic measurements, thermal analysis, electron microscopy (SEM and TEM) and ionic conductivity experiments. The temperature dependence of the longitudinal ultrasound attenuation and velocity showed anomalous attenuation peaks and sudden unusual relative sound velocity changes near 330 and 341 K, indicating that possible structural changes and softening of interatomic bonds occurred. These are consistent with the anomalous changes of ionic conductivity of the same samples. Thermal analysis revealed that such anomalous changes are directly related to the glass transition and the microcrystalline formation, respectively. Moreover, direct evidence for the processes of crystallizations above 344 K were given from our SEM and TEM study. Therefore, it is suggested that the observed anomalous enhancements near 326 and 344 K of ionic conductivity of this amorphous fast ionic conductor is related to the destruction of the amorphous structure and the crystallization of the amorphous state.

ELECTRONIC WEAK LOCALIZATION AND SUPERCONDUCTIVITY FOR YBa2Cu3−xAlxOy (x=0−0.4) SYSTEMS: A POSITRON STUDY

In this paper, we present the positron lifetime data in high Tc cuprate perovskite YBa2Cu3−xAlxOy (x=0−0.4) systems. A significant Al substitution dependence of the positron lifetime parameters was observed, and the local electron density ne and defect concentration Cd were also calculated as a function of Al substitution x. The results show that at low doping concentration, x≤0.15, both ne and Cd exhibit a large change and then reach a limit value of saturation or a peak value above x=0.15 which corresponds just right to the known structural transition from orthorhombic to tetragonal phase. Here, the decrease in ne can be interpreted by weak electronic localization in Cu-O chains. The effect of ne on superconductivity and the mechanisms of positron annihilation were also discussed.

Preparation, structure and properties of Bi-based superconducting fibers grown by laser-floating-zone-growth method

Abstract In this report, we describes investigation of the preparation, structure and properties of Bi-based superconducting fibers grown (polycrystalline, modifying-composition with self-flux and amorphous material) and varying growth condition have been used. We have got the polycrystalline and single-crystal(or called quasi-single crystal) fibers with Tc value of 83–110K and the most Jc vallue of more than 5200A / cm2. The fibers have a good texture structure i.e., its a-b plane is parallel to the growth direction and c-axis is perpendicular to the influence of growth direction. The growth condition, composition of the source materials and post—growth heat treatment have also been discussed.

Ho 0.5 Pr 0.5 FeO 3 的磁性与巨磁介电效应

采用固相反应法制备了Ho 0.5 Pr 0.5 FeO 3 多晶样品, 对其磁性和磁介电特性进行了系统研究。在 T =4.5 K附近存在Ho离子的反铁磁相变, 在T= 59 ~80K可观测到Fe离子的自旋重取向转变, 磁滞回线表明样品呈现弱铁磁性。在 T = 270 K, 介电常数可达~10 3 , 研究表明该介电常数与270 K附近的电阻变化相关联, 该处电阻变小, 介质损耗减小, 导致介电值变大。尤其重要的是, 该样品在室温下表现出磁场诱导的巨磁介电效应, 在频率 kHz、外加磁场为1.6×10 6 A/m下, 其值可达5500%, 该巨磁介电效应可能来源于磁电阻效应。采用固相反应法制备了Ho 0.5 Pr 0.5 FeO 3 多晶样品, 对其磁性和磁介电特性进行了系统研究。在 T =4.5 K附近存在Ho离子的反铁磁相变, 在T= 59 ~80K可观测到Fe离子的自旋重取向转变, 磁滞回线表明样品呈现弱铁磁性。在 T = 270 K, 介电常数可达~10 3 , 研究表明该介电常数与270 K附近的电阻变化相关联, 该处电阻变小, 介质损耗减小, 导致介电值变大。尤其重要的是, 该样品在室温下表现出磁场诱导的巨磁介电效应, 在频率 kHz、外加磁场为1.6×10 6 A/m下, 其值可达5500%, 该巨磁介电效应可能来源于磁电阻效应。

Positron Annihilation During Pre-crystallization Process in an Amorphous Silver Ionic Conductor

The study of positron annihilation on amorphous 0.60AgI-0.25Ag2O-0.15P2O5 has been carried out in the temperature range from 100 to 350 K. The temperature dependence of average lifetime shows anomalous peaks at 208, 228, 325, 338 K indicating possible structure relaxation. Especially the last two peaks reflect the structural changes during pre-crystallization process of the amorphous ionic conductor. These results are consistent with that of ultrasonic attenuation and ionic conductivity experiments on the same samples.