Raman spectra and X-ray diffraction of tuite

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Marco E. Ciriotti
Messaggi: 23496
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Raman spectra and X-ray diffraction of tuite

Messaggio da Marco E. Ciriotti » ven 15 mar, 2013 19:24

Referenza:
▪ Zhai, S., Xue, W., Lin, C.-C., Wu, X., Ito, E. (2013): Raman spectra and X-ray diffraction of tuite at various temperatures. Physics and Chemistry of Minerals, 38, 639-646.

Abstract:
High-temperature Raman spectra and thermal expansion of tuite, γ-Ca3(PO4)2, have been investigated. The effect of temperature on the Raman spectra of synthetic tuite was studied in the range from 80 to 973 K at atmospheric pressure. The Raman frequencies of all observed bands for tuite continuously decrease with increasing temperature. The quantitative analysis of temperature dependence of Raman bands indicates that the changes in Raman frequencies for stretching modes (ν3 and ν1) are faster than those for bending modes (ν4 and ν2) of PO4 in the present temperature range, which may be attributed to the structural evolution of PO4 tetrahedron in tuite at high temperature. The thermal expansion of tuite was examined by means of in situ X-ray diffraction measurements in the temperature range from 298 to 923 K. Unit cell parameters and volume were analyzed, and the thermal expansion coefficients were obtained as 3.67 (3), 1.18 (1), and 1.32 (3) × 10−5 K−1 for V, a, and c, respectively. Thermal expansion of tuite shows an axial anisotropy with a larger expansion coefficient along the c-axis. The isothermal and isobaric mode Grüneisen parameters and intrinsic anharmonicity of tuite have been calculated by using present high-temperature Raman spectra and thermal expansion coefficient combined with previous results of the isothermal bulk modulus and high-pressure Raman spectra.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 23496
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Raman spectra and X-ray diffraction of tuite

Messaggio da Marco E. Ciriotti » sab 28 ott, 2017 14:11

Referenza:
▪ Skelton, R. & Walker, A.M. (2017): Ab initio crystal structure and elasticity of tuite, γ-Ca3(PO4)2, with implications for trace element partitioning in the lower mantle. Contributions to Mineralogy and Petrology, 172, 87; https://doi.org/10.1007/s00410-017-1406-5.

Abstract:
Tuite forms by the breakdown of apatite at high pressure and is thus expected to play a role in extending the phosphorus cycle beyond the stability field of apatite and into the lower mantle. With its large, high-coordination cation sites, tuite is thought to be able to dissolve large quantities of incompatible elements such as rare earth elements, Sr, Th, and U, and is potentially an important mantle reservoir for these elements. In this paper, ab initio calculations of the structure and elasticity of tuite to lower mantle pressure are presented and used to probe trace element incorporation. The calculated zero-pressure volumes of the M1 and M2 cation sites were 50.23 and 36.61 Å3, while the corresponding bulk moduli K0 are 116.1 and 94.2 GPa, significantly lower than the 234.1 GPa calculated for the M site of CaSiO3 perovskite (cpv), another likely host for incompatible elements in the mantle. The partitioning of impurities between tuite and cpv is investigated using a lattice strain model, parameterized by the ab initio calculations, to calculate isovalent substitution energies across a range of pressures and impurity sizes. Additionally, energies of strontium and barium defects in tuite are compared with those of equivalent defects in cpv, and it is found that both elements will partition strongly from cpv into tuite.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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