Raman spectroscopy study of damage induced in fluorapatite by swift heavy ion irradiations

Raman spectroscopy was used to study the radiation damage of fluorapatite single crystals and sinters. Krypton and iodine ion irradiations were performed at high energies (similar to 1 MeV amu(-1)) for fluences ranging between 1 x 10(11) and 5 x 10(13) cm(-2). Evolution of the symmetric stretching mode of the PO43- tetrahedral building blocks (strongest Raman mode observed at 965 cm(-1)) versus ion fluence was investigated. After irradiation, this peak decreases in intensity and a second broader peak appears at lower wavenumber. The well-resolved peak has been assigned to the crystalline phase, and the broader one to the amorphous phase. The integrated intensity ratios of these two peaks versus fluence are in good agreement with the damage fractions determined by X-ray diffraction (XRD). Fits of the amorphous fraction versus fluence show that the amorphization mechanisms is dominated by a single-impact process for iodine ions and by a double-impact process for krypton ions in the case of single crystals and sinters. For both irradiations, complete amorphization could not be obtained. The amorphous fraction saturates at a maximum value of 88% for sinters and 72% for single crystals. This is attributed to a recrystallization effect which is more important in single crystals than in sinters. For both types of samples, the crystalline peak shifts slightly to a lower wavenumber with fluence, and then shifts back to its initial value for an amorphous fraction larger than 60%. This feature is attributed to a stress relaxation, as shown in the XRD data, which is accompanied by a decrease of the crystalline peak full-width at half-maximum. Copyright (C) 2011 John Wiley & Sons, Ltd.