Download Document

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.
100500505a
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
Quartz
plagioclase
Inttnsity, app. un.
Anatase
200
400
Frequency, cm
600
-1
Infrared reflection spectrum
psevdotachilite
40
Quartz
Albite
Intensity, %
30
20
10
0
400
600
800
1000
Frequency, cm
-1
1200
• Measuring Raman and IR spectra we can
determine minerals in rocks
Founded minerals in rocks
Arkosic
Mantle
sandstone :
Xenolith
•Anatase
•Pirope
Quartz
•Quartz
•Omphacite
Albite
•Plagioclase
Psevdotachilite
Form and shift of band in Raman spectra of
arcosic sandstone with nanocrystals anataze
Macro single crystal
Inensity, appr. un.
1,0
0,8
Nanocrystal in arcosic
0,6
sandstone
0,4
0,2
0,0
120
140
Frequency, cm
-1
160
Form and shift of band for nanocrystals
quartz in IR spectra of psevdotachilite
1,0
0,8
Nano in
psevdotahilite
Macro- single
crystal
"
0,6
0,4
0,2
0,0
680
700
Frequency, cm
-1
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:
I   
C0, q  d 3q
2
  q 2  0 22
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
  q 2 L2 
2

C0, q   exp  
2 
 16 
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 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,
1,2GPa
1,8GPa
Increased to 50%
Shift of frequency band for SiOAl 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
Thank for yours attention
very much!