Polarized infrared reflectance spectra of brushite (CaHPO4 center dot 2H(2)O) crystal investigation of the phosphate stretching modes Jean-Yves Mevellec, Sophie Quillard, Philippe Deniard, Omar Mekmene, Frederic Gaucheron, Jean-Michel Bouler, Jean-Pierre Buisson To cite this version: Jean-Yves Mevellec, Sophie Quillard, Philippe Deniard, Omar Mekmene, Frederic Gaucheron, et al.. Polarized infrared reflectance spectra of brushite (CaHPO4 center dot 2H(2)O) crystal investigation of the phosphate stretching modes. Spectrochimica Acta Part A: Molecular and Biomolecular Spec- troscopy, Elsevier, 2013, 111, pp.7. 10.1016/j.saa.2013.03.047. hal-00980658 HAL Id: hal-00980658 https://hal.archives-ouvertes.fr/hal-00980658 Submitted on 29 May 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 111 (2013) 7–13 Contents lists available at SciVerse ScienceDirect Spectr ochimica Acta Part A: Molecul ar and Biomo lecular Spectrosco py journal homepage: www.elsevier.com/locate/saa Polarized infrared reflectance spectra of brushite (CaHPO4Á2H2O) crystal investigation of the phosphate stretching modes ⇑ Jean-Yves Mevellec a, , Sophie Quillard b, Philippe Deniard a, Omar Mekmene c, Frédéric Gaucheron c, Jean-Michel Bouler b, Jean-Pierre Buisson a a CNRS, Institut des Matériaux Jean-Rouxel (IMN) – UMR 6502, Université de Nantes, 2 rue de la Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France b INSERM, UMRS 791, Université de Nantes, Laboratoire d’Ingénierie Ostéo-Articulaire et Dentaire, Faculté de Chirurgie Dentaire, 1 Place Alexis Ricordeau, 44042 Nantes Cedex 1, France c INRA, UMR1253 Science et Technologie du Lait et de l’Oeuf, 65 rue de Saint Brieuc, 35042 Rennes Cedex, France highlights graphical abstract Polarized infrared reflectance measurements from the ac-plane of M 180° 3 TO LO brushite crystal. Dispersion model analysis for 150° M4 monoclinic crystals. Reflectance Oscillators parameters for the P–O 120° À1 stretching modes 800–1200 cm . 90° M2 60° Polarized 30° M1 IR 0° 800900 1000 1100 1200 Wavenumbers (cm-1) article info abstract Article history: Polarized infrared (IR) reflectance measure ments at near-normal incidence were recorded from the ac- Received 8 November 2012 À1 plane of a monoclinic brushite (CaHPO4Á2H2O) crystal in the 800–1200 cm spectral range (P–O stretch- Received in revised form 8 March 2013 ing modes). The adjustment of these data, on the basis of a dispersion analysis (DA) model for monoclinic Accepted 12 March 2013 case, allowed the determination of oscillators parameters for the four P–O stretching observed modes of Available online 23 March 2013 the phosphate group. Ó 2013 Elsevier B.V. All rights reserved. Keywords: IR polarized reflectance spectra Dispersion analysis Monoclinic crystal Brushite Introduction restorative materials based on calcium phosphate, for dental ce- ments and bone implants [1]. Dicalcium phosphate dihydrate (DCPD; CaHPO4 Á2H2O) is known The crystal structure of brushite has been firstly described by as the mineral form ‘‘brushite’’ and it has been largely studied since Beevers [2] in 1958, and investigated by several authors via its discovery in 1865. This compound is of particular importance in X-ray Diffraction [3] or neutron scattering [4] measurements. the biological field. It plays a role in the biomineralization pro- Heijnen and Hartman [5] have also proposed a uniform description cesses and it is actually widely used in the composition of several of this crystal structure with those of gypsum and pharmacolite, although their symmetries are different. Recently, first-principles calculations [6] have been also performed and reproduced well ⇑ Corresponding author. Tel.: +33 0240373975. experimental XRD results. From all these different works, it is as- E-mail address: [email protected] (J.-Y. Mevellec). sumed that the brushite crystal is monoclinic with the following 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.03.047 8 J.-Y. Mevellec et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 111 (2013) 7–13 cell parameters: a = 5.812 Å; b = 15.180 Å; c = 6.239 Å; b = 116.25° However, our XRD data allowed a clear knowledge of the geometry and Z = 4 in the Ia space group. An equivalent description of the of our crystal and its well-defined orientation for further spectro- structure can be obtained in the Cc space group, with transformed scopic measurements. cell parameters of a = 6.358 Å, b = 15.180 Å, c = 5.812 Å and The crystal used for the infrared reflectance data have dimen- b = 118.51° . sions of about 650 lm  300 lm  40 lm. In Fig. 1, a scheme of Vibrational spectroscopic investigations on monocrystals are the studied crystal is depicted showing crystal axis and orientation useful to evidence the polarization of the different modes and of the faces (Miller indices). the possible TO–LO splitting due to their polar character. Particularly, infrared reflectance measurements can provide Infrared measurements valuable information on the optic, dielectric and dynamic parame- ters of a single crystal. In 1970s, Koch and Otto [7] and later Belou- The FTIR absorbance of DCPD powder was measured on a Bru- sov and Pavinich [8] reported a model to obtain dispersion ker Vertex 70 spectrometer, using KBr pellet technique. Near-nor- parameters of monoclinic crystals and to calculate the oscillators mal infrared specular reflectance data were obtained on a Bruker strengths from the LO–TO frequency separation. Pavinich et al. ap- Microscope Hyperion 2000 equipped with a Mercury–Cad- plied this model to the spodumene crystal LiAlSi2 O6 [9] and later, mium–Telluride detector and coupled with the Vertex 70 spec- based on this previous model, some authors have successfully trometer. The analyzed surface was 100 lm  100 lm. Infrared studied the behavior of other monoclinic compounds, like gypsum polarizer was placed on the incident beam. All the spectra and Tutton salts [10,11]. In this work, we have chosen to use a sim- (4 cmÀ 1 as spectral resolution, 100 scans) were background cor- ilar, but simplified, dispersion analysis model to investigate the rected using reflection on gold surface. The Cassegrain infrared polarized reflectance results of brushite monocrystal. concentrator, focusing the IR beam on the sample, has a numerical In such monoclinic crystals, only one of the crystallographic aperture of 0.4. Thus, the collecting cone for this objective has an axes (the b-axis) coincides with one of the dielectric tensor axes effective half angle of 23.6° , this value is an angular limit for the for all frequencies, while the other two principal axes lie in the IR rays. A recent work [17] presents comparative results of reflec- ac-plane. These principal dielectric tensor axes are frequency tance for different incident angles, showing errors can appear from dependent in the ac-plane as each polar phonon oscillator is char- an angle of 16 °. In spite of this, we suppose the incident and re- acterized by its own orientation. Then, the polarized reflection flected beams near-normal to the main surface of the crystal (ac- spectra obtained from the monoclinic plane (ac-plane) are particu- plane) and the corresponding electric fields are assumed to be in larly interesting to evidence the difference in the orientation of the this plane. So our approximations are afterward justified by the dipole moments in this plane, together with their dynamic param- quality adjustment between experimental and calculated results eters (strength, damping). for this material. Located in the 800–1200 cmÀ 1 spectral range, the P–O stretch- ing modes of such orthophosphates crystal are intense and well Theoretical calculations separated either in Raman and infrared spectroscopies, and no other bands are expected in this frequency range. Moreover, they In order to interpret the experimental reflectance data, we car- showed a significant sensitivity to changes in the structure such ried out calculations based on a dispersion analysis model, briefly as calcium substitution by other cations, as it has been reported described below in this paper (see Theoretical model part). The in previous studies on brushite itself [12] and on other orthophos- simultaneous fitting of eight selected reflectance spectra was per- phates [13,14]. A clear knowledge of these modes and of their pos- formed using least squares refinements by our visual basic pro- sible mixing is then of particular interest. For these reasons, we gram. In this aim, 19 parameters; four for each mode and three have restricted this vibrational study to the P–O stretching vibra- for the high-frequency permittivity tensor were adjusted. tions of this group. Results and discussion Materials and methods As explained in the introduction, we have focused our attention Preparation of crystals on stretching vibrations of the phosphate groups. In this crystal, it should be noted that the phosphate group is asymmetric with four Brushite crystals were prepared by dissolution of commercial non-equivalent P–O bonds. Thus, the P–O bond with the hydroxyl dicalcium phosphate dihydrate (Riedel-de Haën, Germany) in di- oxygen (noted P–OH) has a length significantly longer than the lute acetic acid [15]. After evaporation (heating at 70 °C), pre- others (1.599 Å and 1.515, 1.534, 1.516 Å respectively). Conse- dominant small tabular {0 10} crystals were obtained and quently, local symmetry on one phosphate group can be assumed washed with ethanol.