MICROSTRUCTURE, THERMOELECTRIC-POWER AND MAGNETIC IRREVERSIBILITY OF COPRECIPITATED YBA2CU4O8 POWDERS

Abstract

The details of microstructure of triethylammonium oxalate coprecipitated YBa2Cu4O8 powders (T(c) = 83 K), prepared under one atmosphere of oxygen, were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and selected area electron diffraction (SAED). The coprecipitated powders are characterized by a submicron particle size and homogenous chemical composition of Y 1.0(3)Ba2.0(1)Cu4O8 as determined by SEM and EDS, respectively. The electron diffraction spots along the c* direction of the coprecipitated YBa2Cu4O8 microcrystals have extended streaks corresponding to a defect stacking fault. The YBa2Cu4O8 material, as prepared, is under-doped as compared to (Y0.9Ca0.1)Ba2Cu4O8 (T(c) = 88 K) as evidenced by thermoelectric power measurements. The observed magnetic irreversibility line for YBa2Cu4O8 shifts to lower temperatures as compared to that for YBa2Cu3O7; this may arise from the reduced structure dimensionality of YBa2Cu4O8 as compared to that of YBa2Cu3O7. The upper critical field [H(c)2(0)] and the Ginzburg-Landau coherence length (zeta) of the YBa2Cu4O8 material are determined to be 117 T and 17 angstrom, respectively.