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

The series of complex oxides, La2 -xSrxNi1 -yMnyO4 -δ (х = 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°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 ± δ. At room temperature, the solid solutions LaSrNi1 -yMnyO4 ± δ (y = 0.1, 0.3, 0.5, and 0.7) show a small excess of oxygen (δ > 0) which increases with the manganese doping level y. Total conductivity and Seebeck coefficient were determined in air from room temperature to 1100°C, with the maximum value ~ 100 S/cm for La1.2Sr0.8Ni0.9Mn0.1O4 ± δ and La1.3Sr0.7Ni0.9Mn0.1O4 ± δ. 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 μV/K.