Superiority of nitrate decomposition method for synthesis of K 2NiF 4-type La xSr 2− xMnO 4 catalysts

Abstract

K 2NiF 4-type La 0.2Sr 1.8MnO 4 was synthesized by nitrate (ND) and nitrate/acetate (NAD) decomposition methods as well as solid-state reaction. Single-phase oxide was obtained at 550 °C by the ND method just after the decomposition of Sr(NO 3) 2 and at 1000 °C by the NAD method after the decomposition of SrCO 3. The K 2NiF 4-type oxide was hardly formed by the solid-state reaction. In the La–Sr–Mn system, an intermediate compound of SrCO 3, if present or formed during the decomposition process, interfered with the low-temperature formation of the K 2NiF 4-type oxide because of its high decomposition temperature about 1000 °C. The ND method used only metal nitrates and no starting materials with carbon source, so that the low-temperature synthesis of the K 2NiF 4-type oxide was realized without forming obstinate intermediate compound of SrCO 3. The low-temperature synthesis was possible for La x Sr 2− x MnO 4 with the substitution of La (0 < x < 0.5) and not for La 0.2A 1.8MnO 4 (A = Ca and Ba). The effect of A-site cations on the K 2NiF 4-phase formation was discussed from the geometric aspect.