THE MICROSTRUCTURE OF SUPERCONDUCTING LA2-XKXCUO4-Y (X = 0.22)

Superconducting La1.78K0.22CuO4-y has been studied by means of X-ray d iffraction, scanning electron microprobe and transmission electron mic roscopy, in order to characterize the relative distribution of K withi n these samples. From microprobe and X-ray diffraction data, these mat erials appear to be homogeneous and show a tetragonal structure (a con gruent-to 3.77 angstrom, c congruent=to 13.3 angstrom). Nevertheless, as shown below, X-ray microanalysis, electron diffraction and low reso lution electron microscopy studies indicate that, on a local scale, th e situation is more complex and different modulated structures based o n a tetragonal La2CuO4 subcell are present.