Structural and electrical properties of strontium substituted Y₂BaNiO₅

Highlights: • Limit of solid solution of system Y_2−xSr_xBaNiO₅ shown to be at x = 0.2. • Characterization of the electrical behaviour in the positive temperature range, 100–700 °C. • Conductivity shown to be independent of pH₂O and pO₂. • Low activation energies demonstrated for electrical conduction (0.216–0.240 eV). - Abstract: The Y_2−xSr_xBaNiO₅ (x = 0, 0.1, 0.2 and 0.3) acceptor substituted system has been synthesized by solid state reaction. Structural and microstructural properties have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Lattice volume is shown to decrease linearly with increasing Sr content until composition x = 0.2, highlighting the limit of the solid solution. The electrical response in the temperature range (700–100 °C) was assessed by A.C. impedance spectroscopy in wet and dry O₂ and N₂ atmospheres. Conductivity measurements as a function of oxygen partial pressure (pO₂) were also performed. The data reveal that the conductivity Y₂BaNiO₅ can be increased by one and half orders magnitude by Sr-doping and is independent of both water vapour and oxygen partial pressures (pH₂O and pO₂). The low activation energy for electrical conduction (0.216–0.240 eV) suggests a thermally activated electron hopping mechanism, while the observed pO₂ and pH₂O independence of conductivity suggests that charge compensation for Sr is predominantly by formation of Ni³⁺ rather than formation of oxygen vacancies