Transmission electron microscopy characterization of the high-Tc superconductor HgBa2Ca3Cu4O 10+ delta

The structures of HgBa 2 Ca 3 Cu 4 O 10+δ (Hg-1234) samples have been characterized by means of high-resolution electron microscopy, electron diffraction, X-ray energy-dispersive spectroscopy (XEDS) and electron-energy-loss spectroscopy (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 electron 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 HgO δ layers, leading to the breakdown of the (001) mirror symmetry of the basic structure. XEDS compositional analyses showed a depletion of mercury for the modulated Hg-1234 compared with the unmodulated Hg-1234, while EELS analysis suggested the presence of carbon in the modulated Hg-1234 phase. In addition, a side-centred ordered (Cu,Hg)-1223 phase with low mercury content was identified as one of the major impurity phases in the Hg-1234 samples.