La and Sr substituted Pr2NiO4+delta: Oxygenation and electrical properties

We report herein results concerning the solid solutions Pr2-xMxNiO4+delta, M= La, Sr. These two cations are larger than praseodymium and lead to a structural stabilization, The oxygen excess delta decreases with x for La and Sr substituted Pr2NiO4+delta, Both cases suggest that structural strain is a leading factor for the oxygenation ability of the title compounds, From the evolution of tell parameters, we suggest a phase transition for La substituted compounds occurring for x similar to 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%) far x < 0.5, The Pr2-xSrxNiO4+delta solid solution shows an anomalous behavior for x= 0.5 corresponding to Ni2+/Ni3+ = 1. This anomaly combines an enhancement of the cia ratio, a larger resistivity, and a peak for the activation energy of the resistivity versus T. (C) 1997 Academic Press.