High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2-xSrxNiO4-\delta (x = 1 and 1.4)

TL;DR

This study investigates how high levels of strontium substitution affect oxygen non-stoichiometry, conductivity, and structure in La2-xSrxNiO4- phases at high temperatures, revealing significant changes in oxygen vacancies and nickel oxidation states.

Contribution

It provides new insights into the temperature-dependent oxygen vacancy behavior and structural variations in highly strontium-doped nickelates, expanding understanding of their properties.

Findings

Oxygen vacancy fraction increases with temperature.

Electrical resistivity and thermal expansion vary peculiarly with temperature.

Nickel oxidation state shifts from Ni3+/Ni4+ to Ni2+/Ni3+ on heating.

Abstract

Oxygen nonstoichiometry, electrical conductivity and thermal expansion of La2 xSrxNiO4-\delta phases with high levels of strontium substitution (1 =< x =< 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20-1050 degrees C. These phases retain the K2NiF4-type structure of La2NiO4 (tetragonal, space group I4/mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La2NiO4$\pm$\delta in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni3+/Ni4+ to a Ni2+/Ni3+ equilibrium on heating.