Synthesis, oxygen nonstoichiometry and total conductivity of (La,Sr)2(Mn,Ni)O4±δ

The series of complex oxides, La2-xSrxNi1-yMnyO4-delta (x = 0.7-1, y = 0.1, 0.2, 0.3, 0.5, 0.7), were synthesized via glycine-nitrate and citrate-nitrate combustion techniques followed by sintering at 1350-1400 degrees C in air. All single-phase compounds have the K2NiF4-type structure (sp.gr.I4/mmm). The unit cell volume increases with y and decreases with x in La2-xSrxNi1-yMnyO4 +/-delta. At room temperature, the solid solutions LaSrNi1-yMnyO4 +/-delta (y = 0.1, 03, 0.5, and 0.7) show a small excess of oxygen (delta > 0) which increases with the manganese doping level y. Total conductivity and Seebeck coefficient were determined in air from room temperature to 1100 degrees C, with the maximum value similar to 100 S/cm for La1.2Sr0.8Ni0.9Mn0.1O4 +/-delta and La1.3Sr0.7Ni0.9Mn0.1O4 +/-delta. The conduction is temperature activated for all phases under study. Seebeck coefficient has tendency to decrease from low temperature to high temperature and predominantly adopts slightly negative values varying from -15 to -5 mu V/K. (C) 2015 Elsevier B.V. All rights reserved.