Coexisting hydroxyl groups and H2O molecules in minerals: A single-crystal neutron diffraction study of eosphorite, MnAlPO4(OH)2{middle dot}H2O

Gatta, G. Diego; Nénert, Gwilherm; Vignola, Pietro

doi:10.2138/am.2013.4438

Cited by 10 publications

(26 citation statements)

References 16 publications

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“…For the calculated line shape shown in Figure 3, the adjusted values for d Fe and DE Q were 1.25 ± 0.02 and 1.88 ± 0.03 mm/s (V zz < 0), respectively. They are not highly accurate (see Table 1), but in reasonable agreement with the values expected from the results derived from the zero-field quadrupole doublets in the vicinity of 250 K. The value of 0.45 ± 0.05 for the asymmetry parameter implies that the symmetry of the Mn octahedron is non-axial, which is conceivable considering the known variations in O-O interatomic distances for that octahedron (Hoyos et al 1993;Gatta et al 2013). Calculated values of the field reduction parameters are H xx = -5 ± 1 kOe, H yy = -9 ± 2 kOe, and H zz = -90 ± 5 kOe.…”

Section: Spectra Analyses and Resultssupporting

confidence: 67%

“…The quantities <r 2 > and <r 4 > appearing in Equation 4 are the expectation values of r 2 and r 4 , related to the radial part of the 5 D wave functions. To calculate the matrix elements of the crystal field Hamiltonian, the ligands were assumed to be point charges with relative positions based on the point symmetry of the Fe 2+ site in eosphorite using the crystallographic data of Gatta et al (2013). Hence, the above summarized approach as used in this work to interpret the observed temperature variation of DE Q , essentially concerns a point-charge calculation of the 5 D level scheme.…”

Section: Discussionmentioning

confidence: 99%

“…Based on single-crystal X-ray diffraction, Hoyos et al (1993) concluded that the two aforementioned O4 sites are both occupied by OH groups. However, a more recent structure refinement using neutron diffraction data for a single-crystal of eosphorite has revealed that only one of the O4 sites is occupied by OH, while the other is occupied by H 2 O (Gatta et al 2013). Thus, the structure can be considered as being composed of chains of MnO 4 (OH,H 2 O) 2 and AlO 2 (OH) 2 (OH,H 2 O) 2 octahedra.…”

Section: Introductionmentioning

confidence: 99%

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Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Alboom

Resende

Costa

et al. 2015

American Mineralogist

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A 57 Fe Mössbauer spectroscopic study of natural eosphorite, (Mn,Fe 2+ )AlPO 4 (OH) 2 H 2 O, is reported. The Mössbauer spectra were collected at temperatures between 295 and 4.2 K. At temperatures exceeding 30 K, the Mössbauer spectra consist of a somewhat broadened quadrupole doublet with a splitting of 1.73 mm/s at 295 K. From the spectrum recorded at 250 K in an external magnetic field of 60 kOe, it is derived that the sign of the principal component of the electric field gradient (EFG) is negative and that the EFG's asymmetry parameter is large (~0.5). From these findings, it is concluded that the octahedral coordination of the ferrous cations exhibits in first order a trigonal compression with a further lowering from axial symmetry due to an additional distortion. The spectrum collected at 4.2 K shows the existence of magnetic ordering. It was analyzed in terms of the full hyperfine interaction Hamiltonian, yielding a magnetic hyperfine field value of 146 kOe and EFG characteristics that are fully in line with those obtained from the external-field spectrum. In the temperature range from 10 to 30 K, the spectra indicate the occurrence of relaxation effects. They could be satisfactorily described in terms of the Blume-Tjon (BT) model for electronic relaxation, assuming a superposition of a slow-and a fast-relaxation component. The observed temperature dependence of the isomer shift is adequately described by the Debye model for the lattice vibrations. The characteristic Mössbauer temperature was found as (360 ± 20) K and the zero-Kelvin intrinsic isomer shift as (1.480 ± 0.005) mm/s. The variation of the quadrupole splitting with temperature is explained by the thermal population of the Fe 2+ electronic states within the T 2g orbital triplet, which is split by the trigonal crystal field in a singlet ground state and an upper doublet state, the latter being further split into two orbital singlets by an additional distortion. The energies of these latter excited states with respect to the ground state are calculated to be 280 ± 20 and 970 ± 50 cm -1 , respectively, based on a point-charge calculation of the 5 D level scheme. This calculation confirms the sign of the V zz component of the electric field gradient being negative as it is determined from the external magnetic field measurement and from the magnetic spectrum acquired at 4.2 K. Iron phosphates are widely spread minerals in the Earth's crust and are expected to occur in soils and rocks on Mars as well. Mössbauer spectroscopy as complementary source of information to the results of other analytical techniques, could therefore be useful to identify and characterize the environmental Fe-bearing phosphates.

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Section: Spectra Analyses and Resultssupporting

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Alboom

Resende

Costa

et al. 2015

American Mineralogist

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“…As highlighted by Hawthorne (1998) and Gatta et al (2013), these phases in both their structure and amount of incorporated water provide important clues to the conditions under which they formed, the point being that modest changes in conditions can destabilize one phosphate phase and cause it to be replaced by another one.…”

Section: Development Of a New Chemical And Structural Model For Bone mentioning

confidence: 99%

Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral

Pasteris

Yoder

Wopenka

2014

American Mineralogist

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Despite numerous analytical studies, the exact nature of the mineral component of bone is not yet totally defined, even though it is recognized as a type of carbonated hydroxylapatite. The present study addresses the hydration state of bone mineral through Raman spectroscopic and thermogravimetric analysis of 56 samples of carbonated apatite containing from 1 to 17 wt% CO 3 , synthesized in H 2 O or D 2 O. Focus is on the relation between the concentration of molecular water (as distinguished from hydroxyl ions) and the concentration of carbonate in the apatite. Raman spectra confirm the presence of molecular water as part of the crystalline structure in all the aqueously precipitated carbonated apatites. TGA results quantitatively document that, regardless of the concentration of carbonate in the structure, all hydroxylapatites contain ~3 wt% of structurally incorporated water in addition to multiple wt% adsorbed water. We spectroscopically confirmed that natural bone mineral also contains structurally incorporated molecular H 2 O based on independent analyses of bone by means of spectral stripping (subtracting the spectrum of collagen from that of bone) and chemical stripping (chemically removing the collagen content of bone prior to analysis). Taken together, the above data support a model in which water molecules densely populate the apatite channels regardless of the abundance of hydroxyl vacancies. We hypothesize that water molecules keep the apatite channels stable even when 80% of the hydroxyl sites are vacant (typical in bone), hinder carbonate ions from substituting for hydroxyl ions in the channels, and help regulate chemical access to the channels (e.g., ion exchange, entry of small molecules). Our results show that bone apatite is not a "flawed hydroxylapatite," but instead a definable mineralogical entity, a combined hydrated-hydroxylated calcium phosphate phase of the form Ca 10-x [(PO 4 ) 6-x (CO 3 ) x ](OH) 2-x ·nH 2 O, where n ~ 1.5. Water is therefore not an accidental, but rather an essential, component of bone mineral and other natural and synthetic low-temperature carbonated apatite phases.

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“…This led to a poor description of the ( A comparison between the experimental findings of this study and those of a recent study by Frost et al (2013), based on Raman and infrared spectroscopic characterization of a paravauxite from the Siglo Veinte Mine, Bolivia, is carried out. This present paper contributes to a series on complex H bonding in phosphates (Gatta et al, 2013a(Gatta et al, ,b, 2014.…”

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confidence: 82%

On the complex H-bonding network in paravauxite, Fe²⁺Al₂(PO₄)₂(OH)₂·8H₂O: A single-crystal neutron diffraction study

2014

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The crystal structure and the chemical composition of a paravauxite from the Siglo Veinte Mine, Llallagua, Bustillo Province, Potosi Department, Bolivia [ Fe (Fe 2+ 0.916 Mn 2+ 0.016 Mg 0.064 Ca 0.002 ) S0.998 Al(1)Al(2) Al 2.005 P (P 1.998 Si 0.002(2)º and g = 72.29(2)º, space group P1 ], was investigated by single-crystal neutron diffraction and electron microprobe analysis in wavelength-dispersive mode. Neutron-intensity data were collected at 293 K and anisotropic structure refinement was performed. At the end of the refinement no peak larger than Ô1.3 fm/Å 3 was present in the final difference-Fourier map of the nuclear density. The final statistical index was R 1 = 0.0495 for 194 refined parameters and 1678 unique reflections with F o

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Coexisting hydroxyl groups and H2O molecules in minerals: A single-crystal neutron diffraction study of eosphorite, MnAlPO4(OH)2{middle dot}H2O

Cited by 10 publications

References 16 publications

Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral

On the complex H-bonding network in paravauxite, Fe²⁺Al₂(PO₄)₂(OH)₂·8H₂O: A single-crystal neutron diffraction study

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Coexisting hydroxyl groups and H2O molecules in minerals: A single-crystal neutron diffraction study of eosphorite, MnAlPO4(OH)2{middle dot}H2O

Cited by 10 publications

References 16 publications

Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Mossbauer spectroscopic study of natural eosphorite, [(Mn,Fe)AlPO4(OH)2H2O]

Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral

On the complex H-bonding network in paravauxite, Fe2+Al2(PO4)2(OH)2·8H2O: A single-crystal neutron diffraction study

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On the complex H-bonding network in paravauxite, Fe²⁺Al₂(PO₄)₂(OH)₂·8H₂O: A single-crystal neutron diffraction study