Optical investigation of Prussian blue analogue films against d-electron number

概要

The physical properties of transition metal compounds depend on the number of delectrons (nd). For example, Niedermayer, et al. show successive characteristic magnetic
ordering against nd [1.1, 1.2]. On the other hand, several tranmsition metal compounds
exhibit metal-insulator transition, [1.3, 1.4] superconducting transition [1.5, 1.6] with
decreases in nd. The investigation of the physical properties against nd has given us
perspective view on the transition metal compounds. The most common way to control
the nd in transition metal compounds is to replace the trivalent rare earth metals with
divalent alkaline earth metals. [1.7, 1.8] Another way is to use the electrochemical
oxidization/reduction process in transition metal compounds.
In this thesis, we applied the electrochemical control of nd in Prussian blue analogues
can do. Prussian blue analogues (PBAs), AxM[Fe(CN)6]y zH2O (A is alkali metal; M = Mn,
Fe, Co, Ni, Cu, and Cd), consist of a three-dimensional jungle-gym-type host framework
and guest Na+ ions and H2O molecules (Fig. 1.1). The guests are accommodated in the
nanopores of the framework. PBAs usually show face-centered cubic (fcc; Fmm; Z = 4)
or trigonal (Rm; Z = 3) structures. [1.9] PBAs are attracting the current interest of
materials scientists. This is because they are not only promising cathode materials for
sodium-ion secondary batteries. [1.10-15] For example, in NaxCo[Fe(CN)6]0.90 2.9H2O
(NCF90) thin film shows a discharge capacity of 135 mAh/g and average voltage of 3.6
V. [1.12] In addition, they exhibit interesting physical properties, such as electron transfer
(ET) phase transitions [1.16-19] and light-induced spin state transitions (LISST). ...

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