Oxygen non-stoichiometry and electrical conductivity of Pr2−xSrxNiO4±δ with x = 0–0.5

Oxygen non-stoichiometry and electrical conductivity of the Pr2−xSrxNiO4±δ series with x = 0.0–0.5 were investigated in Ar/O2 (pO2 = 2.5 to 21 000 Pa) within a temperature range of 20–1000 °C. The equilibrium values of oxygen non-stoichiometry and electrical conductivity of these nickelates were determined as functions of temperature and oxygen partial pressure (pO2). The nickelates with x = 0–0.5 appear to be p-type semiconductors in the investigated temperature and pO2 ranges. The nickelates with x = 0.3–0.5 show very feebly marked pO2 dependencies of the conductivity. Pr1.7Sr0.3NiO4±δ shows the anomalies of the conductivity versus oxygen partial pressure which can be related to the orthorhombic–tetragonal crystal structure transformations. The conductivity of the Pr2−xSrxNiO4±δ samples correlates with the average oxidation state of the nickel cations. The samples with x = 0.5 have the highest nickel oxidation state (≈ 2.5+), the highest [Ni3+]/[Ni2+] ratio close to 1 and show the highest conductivity (≈ 120 S/cm) in the whole pO2 and temperature ranges investigated.