Technical Report of ISSP Ser. A: Number 2953

Abstract

Oxygen nonstoichiometry and structural phase transitions in La2NiO(4+delta) were studied by Thermogravimetry (TG) and in situ powder X ray diffraction. Doubly charged O(2-) ions are proposed for species of the excess oxygen from thermodynamical analysis of TG data. A transition from tetragonal I4/mmm to orthorhombic Fmmm phase was found in the wide range where delta is greater than or equal to 0.06 and less than 0.11, which showed a significant time dependence. The phase segregation of pseudo-tetragonal phase from tetragonal I4/mmm was observed in the case where delta is greater than or equal to 0.03 and less than 0.06. The equilibrium phase diagram of La2NiO(4+delta) is proposed in the case where delta in greater than or equal to 0 and less than or equal to 0.18. The character of the phase transitions is discussed in the light of the temperature dependence of the orthorhombicity in each orthorhombic phase.

La2NiO4+δにおける酸素の非化学量論および構造的相転移を熱重量測定法(TG)とその場粉末X線回折によって調べた。TGデータの熱力学的解析から過剰酸素の化学種として2重に荷電したO(2-)イオンを提案した。0.06≦δ＜0.11の広い領域では正方晶系I4/mmmから斜方晶系Fmmm相への転移が起こり、しかも顕著な時間依存性を示すことが分った。0.03≦δ＜0.06では正方晶系I4/mmmから擬正方晶相への相偏析を観測した。0≦δ≦0.18ではLa2NiO(4+δ)の平衡状態図を示した。各斜方晶相における斜方晶性の観点から相転移の特性を議論した。