A Spectroscopic and Structural Study of M(3d)2+ – Doped β-Tricalcium Phosphate – the Binding Properties of Ni2+ and Cu2+ in the Pseudo-octahedral Ca(5)O 6 Host-Sites.
Résumé
The pseudo-octahedral Ca(5)2+ position in β-Ca3(PO4)2 is a higly interesting host site with unexpectedly short Ca-O bond lengths, which can be easily substituted by small 3d-cations, such as Ni2+. Also Cu2+ may fully replace Ca(5)2+, leading to remarkably large energetic and steric distortion effects due to Egg Jahn-Teller coupling – with a ground state splitting of about 1.25 eV. The Cu(Ni)-O bond is strongly ionic according to a 3d-mixing coefficient of the eg-electrons around 0.90, as revealed by EPR- and d-d spectroscopy. It is suggested, that the flexibility of the Ca(5)O6 host polyhedra, which lie isolated in the lattice, in respect to deformations and to substitutions by smaller cations is one reason for the practicability of β-TCP as a biocompatible material.
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