Divalent ions of the first series transition elements and Hg were introduced into a cadmium hydroxyapatite Cd
5(PO
4)
3OH by replacing a part of Cd
2+, and the effects on the crystal growths and the structural changes were studied. Cd
2+ can be exchanged with Mn
2+ up to about 30 mol %, with Ni
2+ or Hg
2+ up to about 10 mol %, and with a little amount of Fe
2+ or Cu
2+. It was found that Cd
5(PO
4)
3OH forms a superstructure when it contains a small amount of Mn
2+, Fe
2+, Co
2+, Ni
2+, Cu
2+ or Hg
2+ ion. Infrared spectra of Cd
5(PO
4)
3OH containing these ions show some new bands in addition to those of Cd
5(PO
4)
3OH. The average structures of the crystals containing a small amount of Hg
2+ and Ni
2+, and the superstructure of the crystal containing Mn
2+ were refined with the full-matrix least-squares method, although the amounts and sites of the substituting ions could not be determined except for the crystals containing Hg
2+. The superstructure belongs to
P6
3 (
a=16.1990(3),
c=6.6485(1)Å and
Z=6) and has more distorted PO
4 tetrahedra than the structure of pure Cd
5(PO
4)
3OH.
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