GRAIN-BOUNDARY CHEMISTRY AND WEAK-LINK BEHAVIOR OF POLYCRYSTALLINE YBA2CU4O8

Magnetic-susceptibility and grain-boundary-chemistry data were obtaine d on dense YBa2Cu4O8 (Y 1:2:4) samples. Transmission-electron microsco py showed that the grain boundaries were free of second phases and the dislocation density was low. Cation content, oxygen composition, and hole density were determined by the combined techniques of nanoprobe e nergy-dispersive x-ray spectroscopy and electron-energy-loss spectrosc opy. A total of 25 pairs of grains was analyzed and the results indica ted that grain boundary and bulk compositions do not differ. The relat ive orientations of the crystallites were determined, and the results show that a wide variety of misorientations was sampled. Almost all of the grain boundaries were fully oxygenated and there are no hole defi ciencies, but the magnetic-susceptibilty measurements showed that the material is granular weak linked. These results indicate that Y 1:2:4 is a material in which clean, stoichiometric boundaries still form wea k links.