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

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

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

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: 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

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)Bandwidth 3)Strength to penetrate high pressure vessels 4)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 Diffraction 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 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 GPa –KEY: Allows sampling at multiple points in pressure medium Measuring Material Parameters…

Need higher pressure

Optical Probes Optical Absorption –High pressure melting, crystallization, phase transitions Infrared Spectroscopy –Detailed bonding properties Raman Spectroscopy ( cm -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 Measuring Material Parameters…

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