X-ray spectroscopic analysis of Liesegang patterns in Mn–Fe-based Prussian blue analogs

What is it about?

We performed time-resolved X-ray fluorescence (XRF) and position-dependent X-ray absorption near-edge structure (XANES) measurements on gels containing Mn2+ and [Fe(CN)6]3− ions. Periodic bands that obeyed the empirical scaling laws characteristic of Liesegang bands formed beyond the turbid zone in the water-glass gel. XRF results demonstrated that the turbid zone and the periodic bands contained diffusive Mn and Fe compounds. XANES results indicated that the Fe local structure in the sample tube was nearly independent of positions and was predominantly [Fe(CN)6]. In contrast, the Mn local structure depended on position. FEFF calculations suggested that Mn-Fe-based Prussian blue analogs, of which the most likely local structure is [Mn(NCFe)3O3K3], co-existed with [MnO6-nCln] (n = 0, 1) species and that their compositions were position-dependent.

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Why is it important?

Prussian Blue Analogs (PBAs) have attracted attention, because of their diverse magnetic, photomagnetic, and electrochemical properties. In particular, PBAs comprising Mn ions and [Fe(CN)6] ions (Mn−Fe-based PBAs) are intriguing as parent compounds for new photo-induced magnetic materials with high Curie temperatures and new cathode materials for advanced ion batteries. Although Liesegang patterning of PBAs has not been reported previously, it was evident in our experiments. The combination of periodic precipitation with wet stamping methods has great potential as a simple, bottom-up approach to the fabrication of micro-battery and micro-(photo) magnetic arrays of PBAs.