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

Structure of YSr _{2- x}Ba _xCu _2.8Cr _0.2O _y ( x=0-1.5) superconductors are examined by electron diffraction, HRTEM and electron energy loss spectroscopy (EELS). YSr ₂Cu _2.8Cr _0.2O _y ( x=0) shows incommensurate superstructure with 3.67 a₀ due to lattice strain and mixed intergrowth of -(Cr-Cu-Cu-Cu-Cr)- and -(Cr-Cu-Cu-Cr)- sequences. In the h 0 l electron diffraction pattern the wavevector [∼0.27, 0, 1/2] due to the incommensurate superstructure disappear in the crystal with high Ba contain ( x⩾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 side with increase of Ba content.