Barry J C
Center for Solid State Science, Arizona State University, Tempe 85287-1704.
J Electron Microsc Tech. 1988 Mar;8(3):325-37. doi: 10.1002/jemt.1060080312.
Direct structure images of the YBa2Cu3O7-x high Tc superconducting ceramic (also called the 1-2-3 compound) at 1.7 A resolution have been obtained for the [100] and [001] orientations. It was found that for the purposes of studying oxygen ordering in this compound it is better to use lattice images of lower resolution. The oxygen ordering was studied via the measurement of the bending of (100) and (110) lattice planes on crossing the (110) twin boundaries in crystals oriented in the [001] zone. Significant variations were found in the b/a ratios, owning to a variation in oxygen ordering, between different crystal grains, and between different regions in the same grain. For the three different 1-2-3 samples studied, the average b/a ratio was 1.016, the same value as was found in neutron diffraction studies. The twin boundaries in the orthorhombic 1-2-3 phase are sharp and planar. It seems likely that the transformation from the high-temperature tetragonal phase to the lower-temperature orthorhombic phase is martensitic in nature. A new phase has been discovered on some of the twin boundaries. The new phase can be indexed as tetragonal with a = 7.5 +/- 0.2 A, and c = 6.8 +/- 0.2 A. It is possible that the new phase is stabilized by the stress which occurs at the twin boundaries.
已获得YBa2Cu3O7-x高温超导陶瓷（也称为1-2-3化合物）在[100]和[001]取向、分辨率为1.7埃时的直接结构图像。结果发现，为了研究该化合物中的氧有序化，使用较低分辨率的晶格图像更好。通过测量在[001]区取向的晶体中穿过（110）孪晶界时（100）和（110）晶格平面的弯曲情况来研究氧有序化。发现在不同晶粒之间以及同一晶粒的不同区域之间，由于氧有序化的变化，b/a比值存在显著差异。对于所研究的三个不同的1-2-3样品，平均b/a比值为1.016，与中子衍射研究中发现的值相同。正交1-2-3相中的孪晶界清晰且呈平面状。从高温四方相到低温正交相的转变似乎本质上是马氏体转变。在一些孪晶界上发现了一个新相。新相可标定为四方相，a = 7.5 +/- 0.2埃，c = 6.8 +/- 0.2埃。新相有可能是由孪晶界处产生的应力使其稳定的。
