Study of superconducting and non-superconducting (Cu,Cr)-1212 compounds byhigh-resolution TEM and electron energy loss spectroscopy

Structure of YSr2-xBaxCu2.8Cr0.2Oy (x = 0-1.5) superconductors are examined by electron diffraction, HRTEM and electron energy loss spectroscopy (EELS ). YSr2Cu2.8Cr0.2Oy (x = 0) shows incommensurate superstructure with 3.67a( 0) due to lattice strain and mixed intergrowth of -(Cr-Cu-Cu-Cu-Cr)- and -( Cr-Cu-Cu-Cr)- sequences. In the h0l electron diffraction pattern the waveve ctor [similar to 0.27, 0, 1/2] due to the incommensurate superstructure dis appear in the crystal with high Ba contain (x greater than or equal to 1.0) . This suggests that structural distortion decreases with Ba substitution. At the same time, Cr-L3, L2 edge of EELS spectra shifts toward low-energy s ide with increase of Ba content. (C) 2001 Elsevier Science B.V. All rights reserved.