Crystal and local structure refinement in Ca₂Al₃O₆F explored by X-ray diffraction and Raman spectroscopy

We present a combined structural analysis on the powder of the Ca2Al3O6F phase using X-ray diffraction (XRD) and Raman spectroscopy techniques. The crystal structure of Ca2Al3O6F has been refined in the rhombohedral system, R3[combining macron] space group, a = 17.3237(7) Å, c = 7.00017(4) Å, V = 1819.38(2) Å(3), Z = 6. The Ca2Al3O6F phase consists of almost ideal AlO4 tetrahedrons linked through corners, Ca(2+) ions in voids, and F(-) ions disordered over 6 sites around the Ca2 ion. The two different Ca sites have also been verified by the photoluminescence spectrum and decay curves using Eu(2+) as the probe ion substituted onto the Ca(2+) sites. A lattice dynamics simulation based on the simplified version of the Born-Karman potential model has been produced. Calculated Raman phonon modes agree qualitatively well with the experimental data. The calculations show that the strong line at 538 cm(-1) (Ag) corresponds to the vibrational mode of a six-membered AlO4 tetrahedrons ring, and the line at 572 cm(-1) (Ag) corresponds to the full symmetric vibration of fluorine atoms in the ab crystal plane.