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.

► P(O2) dependence of the phase transition behavior of Nd2NiO4 + δ was investigated.
► Variation of thermodynamic functions by the phase transition was determined.
► Ellingham diagrams of the phase transition was prepared by thermal analyses.
► ΔH° and ΔS° from the diagrams agreed well with the results of thermal analyses.