Specific heat Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular,...

Specific heat

Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular, purple=pyrope, red=CaO

Thermal expansion

Once have F(V.T) -- can get everything

M-G EOS Parameters -- from Stixrude et al, 2005 with modifications

High pressure experiments

2) Anvil Devices: 2 broad types

Static Measurements:

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 multi-anvil KAWAI-type press

Large volume multi anvil cells:

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

3 orders of magnitude higher than DACs!

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: temperatureI: intensity: wavelengthCs: constants: emissivity

Perfect black body: = 1Grey 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

• 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

• Advantages: 1) Focussing (on small samples)2) Bandwidth3) Strength to penetrate high pressure

vessels4) Polarized - elasticity, structure,

density of states

Now: ‘3rd generation’ synchrotron radiation

• Provides Crystal Structure, Density and melting points

• Synchrotron Radiation provides highly collimated x-ray source • Braggs Law: 2q = angle of diffraction

d = spacing of crystal planes = wavelength of X-ray

In-Situ X-Ray DiffractionMeasuring Material Parameters…

€

=2d sin(q)

X-Ray Spectrography

• Use polychromatic X-rays and Be gaskets

• Observe absorption freq.

• Absorption changes with phase

• Observe:– Atomic Coordination– Structures– Electronic/Magnetic Properties

Measuring Material Parameters…

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+

Measurement of Pressure

• Ruby Chips Fluorescence Method– 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

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– 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 compression3) 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!

Raman Spectroscopy

Specific heat Blue=olivine, green=MgO, orange=forsterite, black=Al2O3, brown=grossular,...

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