多晶Nd和SmFe氧化物中电流的显微结构和磁光研究
Combined microstructural and magneto optical study of current flow in polycrystalline forms of Nd and Sm Fe-oxypnictides
摘要：
为了理解为什么多晶超导oxypnictides的颗粒间和颗粒内的电流密度不同的三个数量级，我们进行了磁光和显微结构检查相结合的代表性随机取向的多晶Nd和Sm单层oxypnictides。磁光图像显示，最高的Jc值内观察到的单个晶粒的c轴垂直于观察平面，这意味着晶内电流是各向异性的。低得多的晶间Jc至少部分是由于许多外在因素，因为在许多晶界处发现裂纹和普遍存在的润湿As-Fe相。然而，在高分辨率透射电子显微镜检查下，一些晶界结构清晰。由于整个样品的全球Jc（5 K）值的两个样品的检查是1000-4000 A/cm 2，一些10-40倍，发现在随机的，多晶YBa_2Cu_3O_（7-x），它似乎占主导地位的阻碍晶间电流流动的许多样品是外在的，虽然一些内在的限制电流流过晶界还不能排除。
英文摘要：
In order to understand why the inter- and intra-granular current densities of polycrystalline superconducting oxypnictides differ by three orders of magnitude, we have conducted combined magneto-optical and microstructural examinations of representative randomly oriented polycrystalline Nd and Sm single-layer oxypnictides. Magneto optical images show that the highest Jc values are observed within single grains oriented with their c axes perpendicular to the observation plane, implying that the intragranular current is anisotropic. The much lower intergranular Jc is at least partially due to many extrinsic factors, because cracks and a ubiquitous wetting As-Fe phase are found at many grain boundaries. However, some grain boundaries are structurally clean under high resolution transmission electron microscopy examination. Because the whole-sample global Jc(5K) values of the two samples examined are 1000-4000 A/cm2, some 10-40 times that found in random, polycrystalline YBa2Cu3O7-x, it appears that the dominant obstruction to intergranular current flow of many present samples is extrinsic, though some intrinsic limitation of current flow across grain boundaries cannot yet be ruled out.
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