Lambruschi Et Al #5059 - POSTER x
of 1
Transcript of Lambruschi Et Al #5059 - POSTER x
-
8/11/2019 Lambruschi Et Al #5059 - POSTER x
1/1
E. Lambrusc hi 1, I. Aliat is 1, D. Bersani 1, L. Mantov ani 1, M. Tribaudino 1, P.P. Lo tt ici 1, G. Redhamm er 21Physics and Earth Sciences Department, University of Parma, Parco Area delle Scienze 7/a, 43124 Parma, Italy, [email protected],
2 Department of Materials Science & Physics, Division of Mineralogy, University of Salzburg, Hellbrunnertstrasse 34, A-5020 Salzburg, Austria
Monitoring the behavior of the different chains (Si and Ge) and the effect of the substitution of thecations in M1 site (Mg and Co): All features in germanate spectra are shifted with respect to silicates to lower wavenumbers due to
the substitution of Si4+ with heavier Ge4+, that causes the distortion of tetrahedral and octahedralsites and changes the bond lengths within the polyhedra [6].
The largest shift with respect to silicates is shown by the T-O stretching and chain bending and/orstretching modes.
Co pyroxenes peaks, generally ascribed to M1-O and M2-O bonds stretching, are shifted to lowerwavenumbers with respect to Mg pyroxenes.
Within the two germanates the differences involve also a little shift in the T-O vibrations due to thedifferent crystallographic arrangement.
PYROXENES: chain si l icate minerals : widespread constituents of the Earth crust and of the upper mantle, as well as of rocky planets and meteorites; synthetic pyroxenes used for glass ceramics, and recently Co-based pyroxenes are investigated as ceramic pigments; in addition they are acquiring a lot of interest in solid state physics for their magnetic and multiferroic properties [1,2].General formula of pyroxenes M2M1T2O6 :
M2are the cations (Mg2+, Fe2+, Li+, Ca2+, Na+) in the distorted polyhedron M2, with coordination from 6 to 8; M1are the cations (Co2+, Mg2+, Al3+, Fe3+, Ti3+, Cr3+, V3+) in the regular M1 octahedron, i.e. in a six-fold coordination;
Trefers to the cations (Si4+
, Ge4+
) present into the tetrahedra forming the pyroxene chains.
CaMgGe2O6 CaCoGe2O6
CaMgGe2O6 CaCoGe2O695 90
101 97
150 142
166 155
178 165
191 187
198 -
258 233
275 263
297 283
317 295
342 326
401 388
433 423
460 451
517 514
553 547
726 721
772 756
828 810
857 843
CRYSTAL CHEMICAL RELATIONSHIPS BETWEEN GERMANATES AND SILICATES HAVE ACQUIRED A LOT OFINTEREST: GERMANATES BEHAVE AS HIGH-PRESSURE MODELS FOR CORRESPONDING SILICATES AND THEY CAN
PROVIDE IMPORTANT INFORMATION ON THE HIGH PRESSURE TRANSFORMATIONS OF SILICATES
a = 10.0987(9) b = 8.9777(8) c = 5.4214(5) =105.3729(9)V = 473.93(7) 3
a = 10.1477(5) b = 8.9518(5) c = 5.4274(4) =104.754(5)
V = 476.77(5) 3
Raman spectrum of germanates ischaracterized in analogy with the silicate
[4] by:1) strong T-O stretching modes of Ge and
non-bridging O1 and O2 atoms within theGeO4tetrahedron at ~850 cm-1;
2) peaks due to chain bending and/orstretching at 400600 cm-1, including themost intense peak at ~550 cm-1and few
weak peaks around 400 cm-1;3) peaks below 400 cm-1, ascribed to non-tetrahedral cation vs. oxygen stretching of
M1-O and M2-O bonds.
space group C2/c Factor group analysis at the point
with 20 atoms in the primitive unit cell(Z=2) [3]: 30 Raman active modes (14
Ag+16 Bg)
REFERENCES:[1] Jodlauk S. et al. (2007) Phys. Condens. Matter, 19,432201. [2] Redhammer G. J. et al. (2008) J SolidState Chem., 181, 31633176. [3] Prencipe M. et al.(2012) Eur. J. Mineral., 24, 457-464. [4] Tribaudino M.et al. (2012) Am. Mineral., 97, 13391347. [5]Mantovani L. et al. (2013) Am. Mineral., 98, 1241-1252. [6] Redhammer G. J. and Roth G. (2005) ActaCrystallogr. C, i20i22.
Micro-Raman spectra on powdered synthetic samples of CaCoGe2O6[2] and CaMgGe2O6(and on samples of synthetic CaCoSi2O6[5] and natural CaMgSi2O6[4] for comparison) recorded with 632.8 nmexcitation light from a HeNe laser in a backscattering geometry using a Horiba-Jobin-Yvon LabRAM microspectrometer.
The samples were prepared from mixtures of CaCO3, GeO2, and Co2O3or MgO in the desired stoichiometry. The synthesis was based on ceramic solid-state sintering route at T = 1573 K.
The structure of a germanate-pyroxene isHP C2/c with an higher kinking of the
tetrahedral chain(O3-O3-O3 angle)
High Temperature C2/c
High Pressure C2/c
Table : Main Raman frequencies (in cm-1
) of thegermanate samples.
Projection of monoclinic C2/c pyroxene
along the a axis
T
O3
O1
O2
mailto:[email protected]:[email protected]
