Crystal and local structure refinement in Ca2Al3O6F explored by X-ray diffraction and Raman spectroscopy†
Abstract
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, R space group, a = 17.3237(7) Å, c = 7.00017(4) Å, V = 1819.38(2) Å3, Z = 6. The Ca2Al3O6F phase consists of almost ideal AlO4 tetrahedrons linked through corners, Ca2+ 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 Eu2+ as the probe ion substituted onto the Ca2+ 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.