Variable range hopping conduction and superconductivity in Ru-1222

• Using several y RuSr2Gd1.4Ce0.6Cu2Oy (Ru-1222) synthesized and characterized.
• Superconductivity is observed over a wide range of oxygen content.
• Normal state exhibits 3D variable range hopping (VRH) only for y = 10.5.
• Tc and VRH may be governed by the octahedra in Ru-1222.

RuSr2Gd1.4Ce0.6Cu2Oy (Ru-1222) with several oxygen content y has been synthesized and studied. The normal state may be of different nature including the hopping conduction. Even though the nature of the normal state conduction varies widely, superconducting state is observed over a wider range of oxygen content. A critical oxygen content y = 10.5 is found for which three dimensional variable range hopping conduction (3DVRH) in Ru-1222 is observed in the entire range of temperature. Clearly the origin of the superconducting transition in Ru-1222 may be governed by factors other than the carrier concentration.