Line-broadening effects in the powder infrared spectrum of apatite

Abstract

International audienceThe crystallinity of natural and synthetic apatite samples is often determined from the broadening of m4 PO4 infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study, the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated. The temperature dependence of the infrared spectrum (10-270 K) is used to assess the respective contributions of homogeneous broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties of apatite based on first-principles density functional theory calculations. The linewidth of the weak m1 PO4 absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison, the other more intense PO4 bands are more sensitive to long-range electrostatic effects

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

“…The lattice parameters of DFT relaxed structures of hydroxyapatite and calcite compare well with their experimental counterparts (Table 1) and previous theoretical modelling at the PBE level (Balan et al, 2011). In both cases, calculated lattice parameters are overestimated by $1%, which is a systematic error in density functional theory calculations performed using GGA PBE functionals.…”

Nanoscale infrared spectroscopy as a non-destructive probe of extraterrestrial samples

“…Accordingly, EDS mapping ascribes elemental abundances from these two regions to oligoclase with a slowly varying composition of 20-26 An mol%. Whereas the anorthite and oligoclase phonon bands resolved by nanoFTIR at 910 and 970 cm À 1 appear expectedly sharper than those observed in far-field absorption spectra for powders [55][56][57] at B915 and B990 cm À 1 (Fig. 6e), the measured albite peak is notably broad (70 cm À 1 full-width at halfmaximum; see Supplementary Fig.…”

New Insights in the Ontogeny and Taphonomy of the Devonian Acanthodian Triazeugacanthus affinis From the Miguasha Fossil-Lagerstätte, Eastern Canada

“…Its position in the present study thus corroborates the presence of a F concentration in apatite, consistent with the EDX measurements performed on specific skeletal structures of Triazeugacanthus (Figure 2i-n). The width of this band is dominated by the atomic-scale distortions of the apatite-structure [30] but overlapping with the strong PO 4 anti-symmetric stretching bands affects accurate analysis.…”