Chemically-induced structural deformation of layered perovskite oxides

Abstract

In order to understand the behavior of the crystal lattice deformation induced by the interstitial oxygen formation in La 2 (Ni 0.9 M 0.1 )O 4+δ (M = Fe, Co, Cu), thermogravimetry, coulometric titration, and high temperature X-ray diffraction measurements were carried out in the temperature range between 873 to 1173 K and the P(O 2 ) range between 10−24 to 1 bar. Oxygen content variation under wide range of P(O 2 ) could be successfully evaluated by combining thermogravimetry and coulometric titration techniques. Compared with non-doped La 2 NiO 4+δ , La 2 (Ni 0.9 Fe 0.1 )O 4+δ and La 2 (Ni 0.9 Co 0.1 )O 4+δ have more interstitial oxygen while La 2 (Ni 0.9 Cu 0.1 )O 4+δ have less. Crystal structure at high temperatures was analyzed assuming the tetragonal symmetry, I4/mmm, for all compositions. With increasing interstitial oxygen concentration, the lattice parameter perpendicular to the perovskite layer increased and that parallel to the perovskite layer decreased. Consequently, the change of the cell volume by the interstitial oxygen formation was small, meaning macroscopic chemical expansion is small.