Vettegren Victor Ivanovich, Kulik V.B., and Mamalimov R.I.

Ioffe Physical-Technical Institute, Russian Academy of SciencesSobolev 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. 100500505a

STUDYING OF NANOCRYSATLS IN ROCKS BY RAMAN AND INFRARED SPECTROSCOPY

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 3x3x3

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

Specimen

Mirror

In spectrometer

Laser beam

Scattering light

Scheme of experiments in Infrared spectroscopy

Raman spectrum of Mantle xenolith

200 400 600

Inttn

sity

, ap

p. u

n.

Frequency, cm-1

Anatase Quartz plagioclase

Infrared reflection spectrum psevdotachilite

400 600 800 1000 12000

10

20

30

40

Inte

nsity

, %

Frequency, cm-1

Quartz Albite

• Measuring Raman and IR spectra we can determine minerals in rocks

Founded minerals in rocks

Arkosic

sandstone : •Anatase

•Quartz

•Plagioclase

Mantle

Xenolith

•Pirope

•Omphacite

Psevdotachilite

Quartz

Albite

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

120 140 1600,0

0,2

0,4

0,6

0,8

1,0

Ine

ns

ity

, ap

pr.

un

.

Frequency, cm-1

Nanocrystal in arcosic

sandstone

Macro single crystal

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

680 7000,0

0,2

0,4

0,6

0,8

1,0

"

Frequency, cm-1

Macro- single crystal

Nano inpsevdotahilite

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 of phonons is approximately 1000 vibration periods. During the timethe 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

20

2

32

2q

qdq,0CI

Expression for the shape of the spectral bands is as follows:

Where 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

2

222

16

Lqexpq,0C

Dependence ν(q) for quartz is ν(q) ≈ ν(0) – 4,8q, where 0) is the frequency for single crystal.

We must picked L and (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 Δ of crystal vibrations under stress P

Δ = 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 – 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 mBut 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 P=1 GPa, T=490 K, t=10 min

Quartz in psevdotachilite

0,4 GPa 0,8 GPaIncreased to 2 times

Before P=1 GPa, T=300 K,

Pirope in xenolite 1,2GPa 1,8GPaIncreased to 50%

Before P=1 GPa, T=490 K, t=10 min

P=1 GPa, T=580 K, t=16 min

Albite in psevdotachilite

+2,5(Tensile)

+7(Tensile increased)

-3,5(compressed)

At 490 K tensile stresses increases, but at 580 K change sing

Shift of frequency band for SiOAl vibrations in albite

Conclusion1. 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

Thank for yours attention very much!