Analysis of structural phase transition of Nd2NiO4 + δ by scanning thermal measurement under controlled oxygen partial pressure

The dependence of the structural phase transition behavior of Nd2NiO4 + δ between the tetragonal and orthorhombic phases on the oxygen partial pressure, P(O2), has been investigated by differential scanning calorimetry, DSC, and thermogravimetry and differential thermal analysis, TG-DTA. The structural phase transition temperature, TP, decreased with decreasing P(O2), while the variations of enthalpy, ΔH, entropy, ΔS, estimated from the peak area of DSC signals and oxygen content at the phase transition, Δδ, determined from TG curves, exhibited little dependence on P(O2). From the relationship between Tp and P(O2), the variations of standard enthalpy, ΔH°, and entropy, ΔS°, at the phase transition have been evaluated. By considering Δδ, ΔH° and ΔS° exhibited fair agreement with ΔH and ΔS evaluated by DSC.