Structural Analysis of Hopeite Crystals by Means of Curve Fitting Method of EXAFS

Abstract

EXAFS was applied to analyse the structure of hopeite, specified as Zn3(1104)2.4H 2U and Zns_sMnx(PO4)2.4 H 20. The oxygen corresponding to first neighboring atom of the z inc appeared at 1.46Å and 1.44Å. (Figs.1 and 2). Since ∅(K) contained a deviation of phase shift, these data imply apparent bond distances. Therefore, reverse operation of Fourjer transform and curve fitting were carried out to determine the real bond distances. Th ee results obtained were 1.94Å for the former and 1.96Å for the latter (Figs.3 and 4, Table 1). It was found that the bond \distances expressed Zn-O bond due to a tetrahedron structure of [Zn0₄] in hopeite. The coordination number of zinc atom was about four, revealing the [ZnO₄] structure. Information relating to Zn-O bond of a octahedron structure of [ZnO₂. (H₂O)₄] was not acquired.
Reverse operatio n of Fourier transform and curve fitting of the 2 nd to 4 th peaks were performed (Figs.5 and 6) and found that all the peaks corresponded to a Zn-P relation. The coordination number to zinc for the 2 nd peak was about one. Accordingly, the 2 nd peak contained information about the nearest phosphorus atom to zinc in [ZnO₄] group (Table 1).
There was a difference by 0.5Å for the Zn-O distances between the Fourier transform of EXAFS and the reverse operation of Fourier transform. It was revealed that the difference corresponds to the deviation of phase shift. The bond distances of Zn-O and the interatomic distances of Zn-P were consistent with crystallographic data. The curve fitting method of EXAFS gave significant knowledge including information about coordination number tc characterize hopeite crystals.