Analysis of structural phase transition behavior of Ln2NiO4 + δ (Ln: Nd, Pr) with variation of oxygen content

The orthorhombic-tetragonal structural phase transition behaviors of Pr2NiO4 + δ and Nd2NiO4 + δ were investigated by DSC and TG–DTA under controlled oxygen partial pressure, P(O2), and their difference was discussed. A discrete weight variation originating from the variation of oxide ion content, Δδ, was observed during the phase transition in both Pr2NiO4 + δ and Nd2NiO4 + δ. The Δδ of Pr2NiO4 + δ was larger than that of Nd2NiO4 + δ, and the Δδ of Pr2NiO4 + δ increased with decreasing P(O2), while that of Nd2NiO4 + δ was independent on P(O2), suggesting that not only the valence of Ni but also that of Pr changed during the phase transition in Pr2NiO4 + δ.