Structural Properties and Hopping Conduction in the Normal State of Electron-Doped Superconductor Cuprate Eu_2- Ce ...

Electron-doped superconducting cuprate of Eu_2- Ce CuO_4+α-δ has been studied in the whole doping regime from x = 0.10-0.20 with reducing oxygen content to investigate the relation between the crystal structure and the hopping conduction in the normal state. Parameter of the crystal structure has been extracted from the X-ray diffraction (XRD) measurement while hopping conduction parameters have been obtained from resistivity measurements. The Eu-O bond length decreases with the increasing doping concentration, indicating the successful doping by the partial replacing of Eu³⁺ with Ce⁴⁺. The resistivity increases with decreasing temperature in all measured samples. This is an indication of bad metal-like behavior in the whole regime in the normal state of electron-doped superconducting cuprate of Eu_2- Ce CuO_4+α-δ. The temperature dependence of resistivity was analyzed by the Arrhenius law and the variable range hopping model. It is found that the hopping conduction mechanism more likely follows the variable range hopping rather than the Arrhenius law, indicating that the hopping mechanism occurs in three dimensions. The Cu-O bond length probably plays an important role in decreasing the activation energy. The decreasing value of the activation energy correlates with the increase in the localization radius.