The crystal chemistry of the alkaline-earth apatites A10(PO4)6CuxOy(H)z (A = Ca, Sr and Ba)

The crystal chemistry of the cuprate apatites AI4AII6(PO4)6CuxOy(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