STUDYING OF NANOCRYSATLS IN ROCKS BY RAMAN AND

STUDYING OF NANOCRYSATLS IN ROCKS BY RAMAN AND INFRARED SPECTROSCOPY Vettegren Victor Ivanovich, Kulik V. B. , and Mamalimov R. I. Ioffe Physical-Technical Institute, Russian Academy of Sciences Sobolev G. A. , Kireenkova S. M. , Morozov Yu. A. , Smul’skaya A. I. Institute of Physics of the Earth, Russian Academy of Sciences The work was supported by the Russian Foundation for Basic Research, grant no. 100500505 a

The purposes of this work 1. Search nanocrystals of minerals in deep rock, and their identification; 2. Estimation of their sizes and internal stresses in nanocrystals, 3. Studying the changes in their sizes and internal stresses under compression and high temperature.

Specimens • Rocks: 1. Mantle xenoliths from the kimberlitic tube; 2. Fine-lamellar arkosic sandstone; 3. Pseudotachylite (a product of intensive milling of granite in seismic fault zones). • Form of specimens: quadrate or round plates with dimensions 3 x 3 x 3 cm.

Methods • Raman and Infrared spectroscopy • The dimensions of nanocrystalls was determine by measuring asymmetric broadening of bands in the spectra. • The value of internal stresses in nanocrystals was estimated by measuring the shift of the bands.

Scheme of experiments in Raman spectroscopy

Scheme of experiments in Infrared spectroscopy

Raman spectrum of Mantle xenolith Anatase Quartz plagioclase

Infrared reflection spectrum psevdotachilite

• Measuring Raman and IR spectra we can determinerals in rocks

Founded minerals in rocks Arkosic Mantle sandstone : Xenolith • Anatase • Pirope Quartz • Omphacite Albite • Plagioclase Psevdotachilite

Form and shift of band in Raman spectra of arcosic sandstone with nanocrystals anataze

Form and shift of band for nanocrystals quartz in IR spectra of psevdotachilite

Conclusion • When rocks contains crystals with nanometric dimensions the bands became asymmetrically form and their maximums shifts.

Mechanism of forming bands in Raman and IR spectra • It is well-known that phonons (quantum of vibration of crystalline cells ) interactions each other. Because of the mean life time t of phonons is approximately 1000 vibration periods. During the time the phonon runs a distance Λ about 100 nm. • In result of the interaction of light with the phonon a band in the spectrum became symmetrical dispersion shape. That is why the bands in Raman or IR spectra of single macrocrystals have a symmetrical dispersion shape.

Mechanism of changing shape of bands in Raman and IR spectra • If the dimensions L on crystals are less the Λ vibrations (L<Λ ≈ 100 nm) the band broads asymmetrically. Measuring the value of asymmetrically broadening we can estimate the value of crystal dimension.

What we need know to calculate the sizes? • Shape of the nanocrystal. We assumed that all the nanocrystals have a spherical or plate lake shape. • Wave vector dependence of the frequency.

Expressions for calculating the size of nanocrystals Expression for the shape of the spectral bands is as follows: Where n is frequency, q is wave vector of phonon, Γ is half width of band. If the nanocrystals in the rock have the form of a sphere with diameter L, then Dependence ν(q) for quartz is ν(q) ≈ ν(0) – 4, 8 q, where n(0) is the frequency for single crystal. We must picked L and n(0) which describes the shape of band as accurately as possible.

Founded dimensions of nanocrystals (nm) • In xenolith: pyrope ≈ 20; omphacite ≈ 10. • In arkosic sandstone: anataze ≈ 5 -7; quartz ≈ 7 nm; plagioglace ≈ 20 nm. • In psevdotachilite: • quartz ≈ 70 nm; albite 10 – 30 nm.

Shift frequency vibration of quartz nanocrystals • Frequency ν(0) in single crystal of psevdotachilite in Raman spectra is 464 cm-1 but it is 465, 2 cm-1 in spectra of nanocrystals. Shift is +1, 2 cm-1. • Frequency ν(0) in single crystal in IR spectra of psevdotachilite is 695 cm-1 but in nanocrystals is 497 cm-1. Shift is +2 cm-1. • The same results was taken for other nanocrystals: frequency ν(0) of nanocrystals shift from value of frequency the single macro crystal

It is known that the frequency shifts Δn of crystal vibrations under stress P Δn = αP, where α is a mechanical spectroscopic coefficient. If α is known we can calculated the value of internal stresses P.

Average compression stresses in nanocrystals, GPa Arkosic sandstone : Anatase: - 0. 1 – 0. 2; Quartz 0. 9 – 1. 1 Mantle Xenolith: Pirope – 1. 3 Psevdotachilite: Quartz – 0. 25 Usually nanocrystals are compressed

Variation stresses in nanocrystals, GPa No. area diameter 30 mm 1 2 3 Quartz in Psevdotachilite -0, 3 +0, 48 +0, 05 Quartz in arkosic sandstone -0, 25 -1, 4 -0, 5 Anataze in arkosic sandstone -0, 7 -0, 5 -0, 3 Here + is tensile, - is compressive stresses We see that stresses varies from tensile to compressive ones in areas diameter 30 mm But in average there are compression stresses.

Influence of high temperatures and pressure The high pressure and high temperature experiments were carried out in the modified Bridgman chamber, which had been built by Yu. S. Genshaft.

Influence of high temperatures and pressure on dimension of crystals, nm Before P=1 GPa, T=490 K, t=10 min P=1 GPa, T= 570 K, t=16 min Quartz in psevdotachilite 20 10 - Albite in psevdotachilite 20 13 13 The dimensions of nanocrystals usually decreases under high temperature and pressure

Influence of high temperatures and compression on internal stresses in crystals Before Quartz in psevdotachilite Pirope in xenolite P=1 GPa, T=490 K, t=10 min 0, 4 GPa 0, 8 GPa Increased to 2 times Before P=1 GPa, T=300 K, 1, 2 GPa 1, 8 GPa Increased to 50% Shift of frequency band for Si. OAl vibrations in albite Albite in psevdotachilite Before P=1 GPa, T=490 K, P=1 GPa, T=580 K, t=10 min t=16 min +2, 5 (Tensile) +7 (Tensile increased) -3, 5 (compressed) At 490 K tensile stresses increases, but at 580 K change sing

Conclusion 1. Measuring Raman and Infrared spectra we can found from which minerals the rocks consist. 2. Studying asymmetrically broadening the band in the spectra we can evaluated dimensions of nanocrystallites of the minerals. 3. Measured shift of frequency vibration crystalline cells in nanocrystals we can evaluated value of internal stresses in them.

4. We found that • average dimensions of nanocrystals in rocks varies from 5 (for anataze) to 70 nm (for quartz) • internal compression stresses in nanocrystals varies from 0, 25 to 1. 3 GPa. • Dimensions of nanocrystals decreases but internal compression stresses in them increases as a rule under high presses and temperatures

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