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Open AccessArticle

Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate

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Istituto di Cristallografia—CNR, Via Salaria Km 29.300, 00016 Monterotondo (Rome), Italy
2
Dipartimento Scienze della Terra, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Rome, Italy
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Rutherford Appleton Laboratory, ISIS Neutron and Muon Source, Science and Technology Facilities Council, Didcot OX11 0QX, UK
4
Dipartimento di Scienze, Università Roma Tre, Largo S. L. Murialdo 1, 00146 Rome, Italy
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LNF Istituti Nazionali di Frascati, Via E. Fermi 40, 00044 Frascati (Rome), Italy
6
INGV, Via di Vigna Murata 605, 00143 Rome, Italy
*
Author to whom correspondence should be addressed.
Academic Editor: Natalia V. Zubkova
Crystals 2021, 11(3), 225; https://doi.org/10.3390/cryst11030225
Received: 1 February 2021 / Revised: 15 February 2021 / Accepted: 19 February 2021 / Published: 25 February 2021
(This article belongs to the Special Issue Crystal Chemistry and Properties of Minerals)
A crystal chemical investigation of a natural specimen of whitlockite, ideally Ca9Mg(PO4)6[PO3(OH)], from Palermo Mine (USA), was achieved by means of a combination of electron microprobe analysis (EMPA) in WDS mode, single-crystal neutron diffraction probe (NDP) and single-crystal X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The crystal-chemical characterization resulted in the empirical formula (Ca8.682Na0.274Sr0.045)Σ9.000(Ca0.0340.996)Σ1.000(Mg0.533Fe2+0.342Mn2+0.062Al0.046)Σ0.983(P1.006O4)6[PO3(OH0.968F0.032)Σ1.000]. Crystal-structure refinement, in the space group R3c, converged to R1 = 7.12% using 3273 unique reflections from NDP data and to R1 = 2.43% using 2687 unique reflections from XRD data. Unit cell parameters from NDP are a = 10.357(3) Å, c = 37.095(15) Å and V = 3446(2) Å3, and from XRD, the parameters are a = 10.3685(4) Å, c = 37.1444(13) Å and V = 3458.2(3) Å3. NDP results allowed a deeper definition of the hydrogen-bond system and its relation with the structural unit [PO3(OH)]. The FTIR spectrum is very similar to that of synthetic tricalcium phosphate Ca3(PO4)2 and displays minor band shifts due to slightly different P-O bond lengths and to the presence of additional elements in the structure. A comparison between whitlockite, isotypic phases from the largest merrillite group, and its synthetic counterpart Ca3(PO4)2 is provided, based on the XRD/NDP and FTIR results. View Full-Text
Keywords: whitlockite; calcium phosphates; WDS; NDP; XRD; FTIR whitlockite; calcium phosphates; WDS; NDP; XRD; FTIR
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MDPI and ACS Style

Capitelli, F.; Bosi, F.; Capelli, S.C.; Radica, F.; Della Ventura, G. Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate. Crystals 2021, 11, 225. https://doi.org/10.3390/cryst11030225

AMA Style

Capitelli F, Bosi F, Capelli SC, Radica F, Della Ventura G. Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate. Crystals. 2021; 11(3):225. https://doi.org/10.3390/cryst11030225

Chicago/Turabian Style

Capitelli, Francesco; Bosi, Ferdinando; Capelli, Silvia C.; Radica, Francesco; Della Ventura, Giancarlo. 2021. "Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate" Crystals 11, no. 3: 225. https://doi.org/10.3390/cryst11030225

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