Studies on the transport properties of RuSr2RECu2Oy, RuSr2(RE)2Cu2Oy(RE = Gd, Nd) and RuSr2Gd1.4Ce0.6Cu2O10: Possibility of variable range hopping

We study synthesis, characterization and transport properties of several superconducting and nonsuperconducting ruthenocuprate materials by using different routes. RuSr2(RE)Cu2Oy (Ru-1212) and RuSr2(RE)2Cu2Oy (Ru-1222) have been synthesized using two different rare earths, RE = Gd or Nd. A similar route has been followed for the synthesis of all these four compounds. All ruthenocuprate samples are characterized by using X-ray diffraction (XRD), Scanning Electron Micrograph (SEM) and Energy Dispersive X-ray (EDX). The lattice constants have been extracted and so are the grain sizes. Stoichiometries of several ruthenocuprates have been determined by using EDX spectrum. The resistivities of ruthenocuprates annealed in different conditions have been compared. The resistivity in Gd based ruthenocuprate varies in order of magnitude in comparison to that of ruthenocuprates with Nd. We have studied how the annealing temperature also affects transport properties strongly. Using a different route we have synthesized few RuSr2Gd1.4Ce0.6Cu2O10 which shows insulating to superconductor transition. Three dimensional variable range hopping (3DVRH) may be considered as a possible conduction mechanism in the normal state of superconducting RuSr2Gd1.4Ce0.6Cu2O10.

► Ru-1212, Ru-1222 and Ce doped Ru-1222 have been synthesized and characterized.
► The superconducting properties are observed in (Ru,Gd)-1212 for the annealing at 1050 °C in flowing oxygen.
► The transport in nonsuperconducting (Ru, Nd)-1212 and (Ru,Nd)-1222 are almost insensitive to annealing.
► Normal state of Ce doped Ru-1222 exhibits 3D variable range hopping (VRH).