Oxygen non-stoichiometry and electrical conductivity of Pr 2− xSr xNiO 4± δ with x = 0–0.5

Abstract

Oxygen non-stoichiometry and electrical conductivity of the Pr 2− x Sr x NiO 4± δ series with x = 0.0–0.5 were investigated in Ar/O 2 ( pO 2 = 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 ( pO 2). The nickelates with x = 0–0.5 appear to be p-type semiconductors in the investigated temperature and pO 2 ranges. The nickelates with x = 0.3–0.5 show very feebly marked pO 2 dependencies of the conductivity. Pr 1.7Sr 0.3NiO 4± 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 Pr 2− x Sr x NiO 4± 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 [Ni 3+]/[Ni 2+] ratio close to 1 and show the highest conductivity (≈ 120 S/cm) in the whole pO 2 and temperature ranges investigated.