Effects of oxygen non-stoichiometry and cationic substitutions on the properties of Sr<inf>2</inf>RuO<inf>4+δ</inf>

A systematic study of polycrystalline Sr2RuO4+δ has been carried out by varying its oxygen stoichiometry. The oxygen-annealed sample with excess oxygen (δ = 0.25) exhibits pronounced semiconducting behaviour while the argon-annealed phase without excess oxygen (δ = 0) exhibits degenerate semiconducting behaviour. The conduction mechanism is analysed. The air- and oxygen-annealed phases obey a variable-range hopping (VRH) mechanism. Substitution at the Sr site for the first time by Ca, Ba and La and at the Ru site by Ti, Mn, Li and Pb has been carried out and the resulting properties are studied. Among these substitutions La substitution lowers resistivity and the sample behaves like argon-annealed Sr2RuO4. All other substitutions make Sr2RuO4+δ more semiconducting. © 1998 Elsevier Science S.A. All rights reserved.