Structural and electrical properties of La2−xCaxNiO4+δ (0 ≤ x < 0.4) with regard to the oxygen content δ1

Monophasic samples of La2−xCaxNiO4+δ were prepared in the range between 0 ≤ x < 0.4. Their electrical and structural properties were investigated with regard to the excess oxygen δ. Except for the orthorhombic phase with x = 0.1 and δ = −0.01, all members of the system with higher excess of oxygen or calcium are tetragonal with space group I4/mmm. At temperatures below 300°C, the compounds are thermally activated semiconductors; in the range of higher temperatures, the electrical properties are influenced by oxygen exchange, which depends on the calcium doping level.