Synthesis of (NH₄)_2XLa_1−XSr_X[Fe(CN)₆]·nH₂O from two heteronuclear complexes La[Fe^III(CN)₆]·5H₂O and (NH₄)₂Sr[Fe^II(CN)₆] by mechanochemical process

Abstract

A heteronuclear (NH₄)₂Sr[Fe^II(CN)₆] complex having a tetragonal phase was synthesized from Sr(NO₃)₂ and (NH₄)₄[Fe^II(CN)₆]·nH₂O. A single phase of the heteronuclear (NH₄)_2XLa_1−XSr_X[Fe(CN)₆]·nH₂O complex was synthesized by the coprecipitation for two heteronuclear hexacyano complexes of La[Fe^III(CN)₆]·5H₂O and (NH₄)₂Sr[Fe^II(CN)₆]. In this chemical method, the X value (Sr content) for the complex was lower than that of the starting material. This (NH₄)_2XLa_1−XSr_X[Fe(CN)₆]·nH₂O complex was also obtained by a mechanochemical reaction using a planetary ball-mill for two complexes (Total 0.01 mol = ca. 4 g) of (1 − X)La[Fe^III(CN)₆]·5H₂O and X(NH₄)₂Sr[Fe^II(CN)₆] with a small amount (5 ml) of methanol. The hydration number calculated from the elemental analysis agreed with the estimated values when a hexagonal single (NH₄)_0.8La_0.6Sr_0.4[Fe(CN)₆]·4.2H₂O phase formed for X = 0.4. This reaction for X = 0.4 was also possible for the dry process without methanol. In the case of X > 0.4, the peaks of the SrFe- complex were observed in the XRD pattern. The perovskite phase was directly formed by the thermal decomposition at a low temperature for the milled X = 0.4 complex.