Stangarone Et Al #5061 - POSTER x
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8/10/2019 Stangarone Et Al #5061 - POSTER x
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C. Stangarone1, M. Prencipe2, L. Mantovani1, D. Bersani1, M. Tribaudino1, P.P. Lottici1
1Universit di Parma, Dipartimento di Fisica e Scienze della Terra, Parco Area delle Scienze 7/A, 43124 Parma, Italy, [email protected],2 Universit di Torino, Dipartimento di Scienze Mineralogiche e Petrologiche, via Valperga Caluso 35, 10125 Torino, Italy.
Understanding Raman spectra of spodumene, exploiting the accuracy of the quantum mechanical
calculations with ab initio methods
Spodumene is a Li and Al monoclinic chain silicate belonging to C2/c space group atambient conditions. The vibrational modes at point are 14 Ag+ 16 Bg + 14 Au+ 16Bu. 30 Raman active modes (Ag, Bg) are expected.
Raman spectra (normal modes and intensities) of spodumene have been calculated byCRYSTAL14[1] code (ab initio HF/DFT hybrid), which employs localized gaussian-typebasis sets. The chosen Hamiltonian was WC1LYP [2,3], that provided excellentagreement with experimental data for diopside and jadeite [4,5].
The simulated data have been compared with experimental Ramanspectroscopy measurements on a natural sample of spodumene from a graniticpegmatite in Minas Gerais, Brazil, that was already studied by single crystal X-Ray diffraction [6].
Raman spectra have been collectedon the (100), (010) and (20-3) faces ofa -spodumene (LiAlSi2O6-I) sample,with a Horiba Jobin-Yvon LabRAMapparatus (= 632.8 nm). The crystalhas been mounted on a rotatablegoniometer stage. The Raman spectrawere taken in different geometries
and polarizations in order todiscriminate between Ag and Bgsymmetry modes.
Raman spectrum taken on the (010) face inparallel polarization (PP) of spodumene and thecorresponding calculated intensity pattern,according to CRYSTAL14.
Back-scattering Raman spectra taken in cross-polarization (PV) on different surfaces of spodumene(the asterisks indicate the 16 Bgsymmetry modes) andthe corresponding calculated intensity pattern.Residual Agsymmetry modes are present.
All the 30 (14 Ag+ 16 Bg) expected Raman active vibrational modes have been recognized by the experimental
polarized spectra in different geometries and by crystal rotation techniques
Vibrational patterns of some Agmodes and angular dependence of the intensities
References:[1] Dovesi R.. (2014) CRYSTAL14 User's Manual (University of Torino), [2] WuZ. and Cohen R. E. (2006) Phys. Rev. B 73, 235116, [3] Lee C. et al. (1988)Phys. Rev. B 37, 785-789, [4] Prencipe M. et al. (2012), Eur. J. Mineral. 24,457-464 , [5] Prencipe M., (2012) J. Raman Spectrosc. 43, 1567-1569, [6]Tribaudino M. et al. (2003) Canadian Mineral. 41, 521-527, [7]http://rruff.info/Spodumene/R040050, [8] Pommier C. J. S. et al. (2003) J.Raman Spectrosc. 34, 769775.
ConclusionsThe expected 30 Raman active normal modes of -spodumene have been successfully recognizedon the experimental spectra. Ab initio methods have proved to be an excellent aid for theinterpretation of the Raman spectrum. The chosen hamiltonian (WC1LYP) provided very goodagreement with the experimental frequencies: absolute discrepancy ()is 4.8 cm-1.The analysis of the eigenvectors allowed to relate the Raman features to specific vibrationalpatterns.
Experimental and calculated frequencies (cm-1)
RUFF [7] Pommier [8] CalculatedExperimental:
this work Symmetry species
1 147 130.3 146 -15.7 (Bg )
2 155 132.8 130 2.8 (Ag )
3 185 181.1 186 -4.9 (Ag )
4 227 219.2 226.5 -7.3 (Bg )
5 249 235.6 249 -13.4 (Bg )
6 247 251.1 247 4.1 (Ag )
7 261 260 1 (Bg )
8 288.7 293 -4.3 (Ag )
9 292 295 297.8 297 0.8 (Bg )
10 326 328.2 323 5.2 (Bg )
11 347 330 329 1 (Ag )
12 353 354 349.4 354 -4.6 (Ag )
13 362.3 359 3.3 (Bg )
14 381 382 -1 (Bg )
15 390 392 391.4 392 -0.6 (Ag )
16 416 416 419.1 416 3.1 (Bg )
17 440 441 443.6 441 2.6 (Ag )
18 520 522 522.7 521 1.7 (Ag )
19 538.5 535 3.5 (Bg )
20 545 547.1 543 4.1 (Bg )
21 583 591.5 585 6.5 (Ag )
22 628.1 615 13.1 (Bg )
23 704 708 710.1 705 5.1 (Ag )
24 784 793.2 784 9.2 (Bg )
25 890 880.3 883 -2.7 (Bg )
26 975 972 977 -5 (Ag )
27 1017 1026.8 1020 6.8 (Ag )
28 1053.4 1052 1.4 (Bg )
29 1071 1074.2 1072 2.2 (Ag )
30 1101 1110 1103 7 (Bg )
4.8
Non polarized Raman spectra measured on the (010) face (only Agmode allowed), rotating the sample with a step of 15 from = 0(laser polarization along caxis) to = 360.Crystal rotations around different axes enables discriminating between Agand Bgmodes. Some vibrational patterns are shown (OnbObr :non bridged - bridged oxygens).
(010)
(010)
Single-crystal structure refinements [4]
a() 9.479
b () 8.403
C () 5.223
() 110.14
V (3) 390.6
Total number of reflections 1960
Number of reflections with F> 2.6
Rint % 1.7
R4 1.9
wR2% 6.2
GooF 0.98
Number of parameters 48
(001)
(100)
(010)
Intensity
(a.
u) 1074 cm-1 - antisymmetric
stretching Si-Onb
710 cm-1
Si-Obr-Si
bending
391 cm-1 tilting of Si
tetrahedra
133 cm-1chain rotation and
cation (Li) motions
Bgmodes
Experimental(20-3) PV
Experimental(100) PV
Calculatedspectrumxy polarization
Calculatedspectrumyz polarization
Agmodes
(010) PP
xx polarizations
c
b
0
360
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