Transcript Overheads for third week(revised)

Specific heat
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
Thermal expansion
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
Once have F(V.T) -- can get everything
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
M-G EOS Parameters -- from Stixrude et al, 2005 with modifications
High pressure experiments
Static Measurements:
2) Anvil Devices: 2 broad types
i)
Large volume
multi-anvil press
(MAP)
ii) Symmetric opposed
anvil design (many
different designs
e.g. DAC)
Types of Large Volume Presses
• Piston-Cylinder- 4-6 Gpa
• Multi-Anvil- 25GPa
• Paris-Edinburgh- 12GPa
A large-volume high-pressure
and high-temperature apparatus
for in situ X-ray observation,
‘SPEED-Mk.II’
By Katsura et al
SPEED-Mk.II’ is a multianvil KAWAI-type press
Large volume multi anvil cells:
3 orders of magnitude
higher than DACs!
Large volume: House probes, synthesize larger specimens, some
experiments require large V (e.g. ultrasonic interferometry)
Hydrostatic Pressure: Closer, since squeezing from 8 directions,
But, not easily used with gas pressure medium
Pressures: Top of lower mantle at best with sintered diamonds and
synchrotron radiation
P/T Measurement
• Pressure can be measured by calibrating the
machine to a sample with well known diffraction
patterns, such as NaCl.
• Since this is a large volume press, temperature can
be measured directly with thermocouples.
Diamond Anvil Cells:
Why Diamonds?
Can use: Steel, tungsten carbide, boron carbide,
sapphire, cubic zirconia, sintered diamond,
or single-crystal diamond
Single crystal diamond:
1) Strongest material known
2) Transparent (IR, optical, UV, and X-ray)
3) Non-magnetic insulator: , 
Creating Temperature:
3 ways:
1) External heating
2) Internal heating
3) IR Laser Heating
unheated ruby chips
Sample size
Optics to enlarged image
Pressure medium
P-T gradient
Laser heating - use black body radiation
T: temperature
I: intensity
: wavelength
Cs: constants
: emissivity
Perfect black body:  = 1
Grey body:  < 1
 is wavelength dependent
But dependence not known for
many materials! (known for Fe)
Advances in laser heating…
- Double sided laser heating
- split beam and heat from both ends
- Or mix 2 lasers at different modes - flat T distribution
- Can now get temps ~3000K (+/- 10K) at high P
- Bottom line: use caution when trusting results from laser
heating experiments prior to 1996-98
Pressure media
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low shear strength
Chemical inertness
Low thermal conductivity
Low emissivity
Low absorption of laser light
Ar 8GPa, Ne 20GPa, He >100GPa
Draw back: high fluorescence, high
compressibility
Pressure gradients
Synchrotron Radiation
•
Bi-product of particle accelerators
•
Transverse emission of EM radiation
tangential to ring
•
1)
2)
3)
Advantages:
Focussing (on small samples)
Bandwidth
Strength to penetrate high pressure
vessels
4) Polarized - elasticity, structure,
density of states
Now: ‘3rd generation’ synchrotron
radiation
Measuring Material Parameters…
In-Situ X-Ray Diffraction
• Provides Crystal Structure, Density and melting points
• Synchrotron Radiation provides highly collimated x-ray source
• Braggs Law:   2d sin(q)
2q = angle of diffraction
d = spacing of crystal planes
 = wavelength of X-ray

Measuring Material Parameters…
X-Ray Spectrography
• Use polychromatic X-rays and Be gaskets
• Observe absorption freq.
• Absorption changes with phase
• Observe:
– Atomic Coordination
– Structures
– Electronic/Magnetic Properties
X-ray detected lattice parameters
during a phase transformation
For X-ray studies:
• Know temp gradients
• Suitable pressure mediums
• Angular Diffraction method
• Monochromatic X-rays used
• Best for quantitative intensity
• Precision Lattice Parameter measurement
• Energy Diffraction method
• Fastest method
• Gasket Selection
• Be allows trans-gasket measurements at 4
keV+
• Diamonds allow hard X-rays. 12 keV+
Measuring Material Parameters…
Measurement of Pressure
• Ruby Chips Fluorescence Method
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Freq. shift of ruby with increasing pressure
Linear to 30 GPa
Calibrated to 100 GPa by Raman Spec.
Calibrated to >200 GPa by Gold
Accurate to 15-20% at 200 GPa
Diffuses with temperature (>700K)
Ruby and Diamond Fluorescence overlap
between 120-180 GPa
– KEY: Allows sampling at multiple points in
pressure medium
Need higher pressure
Optical Probes
• Optical Absorption
– High pressure melting, crystallization, phase transitions
• Infrared Spectroscopy
– Detailed bonding properties
• Raman Spectroscopy (10-1000cm-1)
– Most definitive diagnostic tool for the identification of specific
molecules
– Diagnostic evidence for phase transition in simple molecular
compounds
• Brillouin Spectroscopy (<1cm-1)
– Wave velocities and elasticity tensor
– New primary pressure standard
• Fluorescence Spectroscopy
– Electronic states
Measuring Material Parameters…
Raman Spectroscopy
• Raman Techniques
– Measures scattering of monochromatic light due to
atomic vibrations.
• Provides vibration frequencies in a solid
– Temperature = noise : most samples temperature
quenched.
– Synchrotron radiation: a powerful, narrow beam of
highly collimated light source.
• Parameters Measured
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Entropies
Specific Heats
Grüneisen Parameters
Phase Boundaries
Elastic Moduli:
, , Vp, Vs
3 ways to get these:
1) Static compression (no info on shear properties)
2) Shock compression
3) Acoustic vibration (frequencies 10^13 Hz) (applicability?)
Extending elastic observations to higher P-T:
Brillouin Spectroscopy • Optical beam scattered by an acoustic wave
• Compression and dilatation by acoustic wave results in change
in refractive index of material
• Look at Doppler shift of laser frequency - get wave velocity of
the acoustic wave
• can get up to ~60GPa
• at ~2500K in DAC with laser
• (mid lower mantle)
Some conclusions
• Early DAC measurements suspect because
non-hydrostatic
• Still very hard to do simultaneous high T
and P – very few elasticity measurements at
high T
• Pressure calibrations improving and
becoming more consistent – but take care
when using older measurements!
Blue=olivine, green=MgO, orange=forsterite, black=Al2O3,
brown=grossular, purple=pyrope, red=CaO
Raman Spectroscopy