Synthesis, crystal structure and properties of calcium and barium hydroxyapatites containing copper ions in hexagonal channels

Abstract

Coloured ceramic calcium and barium phosphate apatites containing copper ions were prepared by solid state reactions at 1100 °C. Single crystals were grown by melting the ceramics in BiMCuO (M=Ca, Ba) fluxes at 1300 °C, and subsequent controlled cooling. The powders were characterised by X-ray diffraction, IR and UV–vis diffuse reflectance spectroscopy and SQUID magnetometry. The single crystals have empirical formulas Ca 5(PO 4) 3Cu 0.27O 0.86H y and Ba 5(PO 4) 3Cu 0.30O 0.86H y , and crystallise in the apatite structure type (space group P6 3/ m, cell parameters a=9.4303(1), c=6.9069(1) Å for Ca and a=10.2073(1), c=7.7401(1) Å for Ba compounds, Z=2) with linear oxocuprate ions in the hexagonal channels. Atomic parameters as determined by Rietveld refinement were very close to those found for the single crystals. IR spectra showed the presence of hydroxyl groups. Magnetic susceptibility measurements suggested that part of copper has oxidation state +2. Apparently Cu +2-ions are responsible for the strong bands in the visible region of the diffuse reflectance spectra, and the intensive colouration of the samples.