In-Situ Transmission Electron Microscopy and Computer Simulation Study of the Kinetics of Oxygen Loss in Yba 2 Cu 3 O Z
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IN-SITU TRANSMISSION ELECTRON MICROSCOPY AND COMPUTER SIMULATION STUDY OF THE KINETICS OF OXYGEN LOSS IN YBa 2 Cu 3 Oz C. P. Burmestert, L. T. Wille2 , R. Gronskyl, B. T. Ahn 3 , V. Y. Lee3 , R. Beyers3 , T. M. Giir 4 , 4 and R. A. Huggins 1 Department of Materials Science and Mineral Engineering, University of California, and the National Center for Electron Microscopy at Lawrence Berkeley Laboratory, Berkeley, California 2 Department of Physics, Florida Atlantic University, Boca Raton, Florida 31BM Research Division, Almaden Research Center, San Jose, California 4 Department of Materials Science and Engineering, Stanford University, Stanford, California
ABSTRACT High resolution transmission electron microscopy during in-situ quenching of YBa2Cu3Oz is used to study the kinetics of microdomain formation during oxygen loss in this system. Image simulations based on atomic models of oxygen-vacancy order in the basal plane of this material generated by Monte Carlo calculations are used to interpret high resolution micrographs of the structures obtained by quenching. The observed domain structures agree well with those obtained from the simualtions. INTRODUCTION Oxygen ordering in the basal plane plays a vital role in determining the superconducting properties of the YBa2Cu 3Oz system.1 Upon cooling from the disordered, tetragonal phase, parallel O-Cu-O chains develop leading to the formation of the orthorhombic phase (Ortho I), a 90K superconductor, near z = 7. At lower oxygen content, a doubling of the orthorhombic unit cell leads to the formation of the orthorhombic Ortho II phase, a 60 K superconductor, near z = 6.5. Thus an understanding of thermodynamics of oxygen ordering is essential for the development and control of superconducting properties in this material. EXPERIMENTAL High resolution transmission electron microscopy is used to study the kinetics of oxygen loss associated with the low temperature Ortho I to Ortho II transformation. Image simulation using the NCEMSS program2 reveals that small but distinct differences are detectable by HREM between the vanous oxygen ordered structures found in the basal plane of this material (Figure 1). Specimens of highly characterized oxygen content (±0.02 oxygens per formula unit) were prepared using a solid state ionic technique. 3 Transmission electron microscopy was performed using the JEOL 200CX microscope. The sintered material was prepared for microscopy by dry crushing into a fine powder and dispersing onto a lacy carbon grid immediately before observation to minimize specimen exposure to air and moisture.
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Figure 1: High resolution simulated images of the Ortho I and Ortho II structures generated using the NCEMSS program. The Ortho II structure is distinguished from the Ortho I structure by a doubling of the distance in the ao direction between the O-Cu-O chains. Mat. Res. Soc. Symp. Proc. Vol. 169. c1990 Materials Research Society
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Oxygen ordered domain formation is studied by beam heating homogeneous YBa2Cu3Oz to destroy the exist
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