The crystal chemistry of the alkaline-earth apatitesA10(PO4)6CuxOy(H)z (A = Ca, Sr and Ba)

Abstract

The crystal chemistry of the cuprate apatitesA^I₄A^II₆(PO₄)₆Cu_xO_y(H)_z (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu²⁺) but in the calcium and strontium analogues co-exists with minor Cu³⁺. This is in contrast with a previous work where Cu¹⁺ and Cu²⁺ were reported.