Mobile oxygen in layered nickelates of perovskite-type

The influence of the different types of oxygen on the structure and electrical conductivity of the perovskite-type nickelates were investigated. The nickelates La2NiO4+δ, La0,6Sr1,4NiO4–δ, Sr3Al0,75Ni1,25O7–δ were synthesised using the solidstate reaction route. Phase composition was determined by X-ray powder diffraction analysis. The iodometric titration technique was used to specify the oxygen content of the powders. Oxygen desorption and absorption, including oxygen index variation, were investigated by oxygen solid electrolyte coulometry (OSEC). Electroconductive properties of samples were studied by a standard DC four-point method. Utilizing OSEC technique, three mobile and one regular type of oxygen were observed in the perovskite layered nickelates with P/RS and 2P/RS structure. These four types of mobile oxygen differ in the binding energy to the crystal lattice and crystallographic positions. The desorption-sorption processes of various types of mobile oxygen have different effects on the thermal expansion of crystal lattice parameters. The regular oxygen, occupying the apex of octahedron, affects the lattice parameters most prominently. This type of oxygen changes the character of the temperature dependence of specific resistivity sufficiently. Interstitial oxygen does not yield such anomalies.