Transmission electron microscopy characterization of the high-T-c superconductor HgBa2Ca3Cu4O10+delta

The structures of HgBa2Ca3Cu4O10+delta (Hg-1234) samples have been characte rized by means of high-resolution electron microscopy, electron diffraction , X-ray energy-dispersive spectroscopy (XEDS) and electron-energy-loss spec troscopy (EELS) techniques. A modulated structure with a modulation vector of q = (0.036-0.048)b* + 0.5c* was found for Hg-1234. High-resolution elect ron microscopy on the modulated structure revealed slight displacements of atomic layers along the c direction. The anomalous contrast induced by the modulation was observed to be distributed asymmetrically between the HgOdel ta, layers, leading to the breakdown of the (001) mirror symmetry of the ba sic structure. XEDS compositional analyses showed a depletion of mercury fo r the modulated Hg-1234 compared with the unmodulated Hg-1234, while EELS a nalysis suggested the presence of carbon in the modulated Hg-1234 phase. In addition, a side-centred ordered (Cu,Hg)-1223 phase with low mercury conte nt was identified as one of the major impurity phases in the Hg-1234 sample s.