La and Sr Substituted Pr2NiO4+δ: Oxygenation and Electrical Properties

We report herein results concerning the solid solutions Pr2−xMxNiO4+δ,M=La, Sr. These two cations are larger than praseodymium and lead to a structural stabilization. The oxygen excessδdecreases withxfor La and Sr substituted Pr2NiO4+δ. Both cases suggest that structural strain is a leading factor for the oxygenation ability of the title compounds. From the evolution of cell parameters, we suggest a phase transition for La substituted compounds occurring forx∼1–1.2. Surprisingly, this transition has a negligible effect on transport properties. On the other hand, a charge localization linked to the presence of praseodymium is observed. Owing to charge compensation, the Sr substituted compounds have a quasi-constant hole concentration (formally 50%) forx