# Presentation: 661894

## High Pressure Spectroscopic Opportunities (mostly infrared and mostly Earth Sciences) and NSLS-II

- Talk Organization:
- A Brief COMPRES Description/Commercial
- Routine (but important!) Infrared Spectroscopy at High Pressure
- 3) 	More Demanding Synchrotron-based Infrared Spectroscopic Applications
- Today: Focus on infrared--highly complementary techniques include inelastic phonon scattering, X-ray Raman, etc.

## Consortium for Materials Properties Research in Earth Sciences

**Co**nsortium for **M**aterials **P**roperties **R**esearch in **E**arth **S**ciences

- Funded by NSF Division of Earth Sciences [2002-2012]

- NSLS-II Meeting
- July 17-18, 2007

- President: Bob Liebermann, SBU
- Executive Committee;
- Quentin Williams, UC Santa Cruz, Chair
- Mike Brown, U. Washington, Vice Chair
- Carl Agee, U. New Mexico
- Jay Bass, U. Illinois Urbana-Champaign
- Don Weidner, SBU
- Mark Rivers, APS/Chicago, Chair Facilities Committee
- Nancy Ross, Virginia Tech, Chair Infrastructure Committee

- Goals: Facilitate the operation and accessibility of high-pressure beamlines.
- support development of new high-P technologies, and advocate for high-P
- related science and education programs to funding agencies.

## Budget for COMPRES

_**Budget for COMPRES**_
**Past Coop Agreement**
- 2006-07:  $2100K
- Five Year [2002-07]:  $10,800K
**Present budget:**
- 2007-08: $2100K
- 2007-2012: $11,500K
- In 07-08, roughly half of budget
- allocated for technical support,
- equipment at NSLS--X17B, C
- (Multi-anvil, Diamond Cell X-rays)
- and U2A (Infrared of DAC and
- geologic samples)

## COMPRES

- Who is represented: 50 US Member Institutions conducting high-pressure Earth Sciences research.
- Communities ***not*** represented:
- Microfocus infrared and x-ray geosciences users
- 		examples: Stardust Comet 81P/Wild 2 samples, 	lots of micromineralogy of terrestrial and 		meteoritic samples...
- High Pressure Physics, Chemistry and Materials Science

## Advantages of Synchrotron IR for High Pressure Applications

- Microfocus capabilities
- 		Key for laser-heated spots,
- 		Trace constituents (water, etc.)
- Far-infrared intensity
- 		Critical for lattice dynamics; but hard 				w/conventional sources
- 3) 	Rapid measurements--high P kinetics
- 4) 	Reflectance from high pressure samples
- 		Produces constraints on ionic polarizability and 		optical constants, band structure

## A Few High Pressure Earth Sciences Issues addressed by IR spectroscopy

- 1) 	Thermodynamics at extreme conditions--for example, controls temperature distribution within the planet
- Water and carbon storage mechanisms in the Earth
- Structure of magmas/melts/glasses
- Phase transitions and bonding properties of deep Earth constituents.
- Thermal and radiative conductivity of deep Earth constituents.

## Synchrotron Source Advantage

- From: M. Martin, ALS

- Advantages: Signal to Noise, thus spatial selectivity, smaller
- and/or more opaque samples, intensity in far-IR and
- for reflectivity

## NSLS-II Mid-IR Brightness

- H-related Vibs.

- Lattice, Functional
- Group Vibs.

## NSLS-II Very Far-IR Brightness

- Large gap
- dipole magnets enhance far-IR intensity

- Lattice, Functional
- Group Vibs.

## Infrared Anvil Transparency

- Early recognition of spectral limitations of diamonds, as well as sapphire and BN as anvils; SiC is a later addition.

- Lippincott et al., Anal. Chem., 1961

- SiC (moissonite) at High Pressures:
-    Liu, Xu, Scott, Williams, Mao, Hemley, RSI, 2004

## FTIR: Basically, Pretty Simple Optics and, an ideal combination with a synchrotron

- No requirement that the light be IR!
- Resolution  1/2xmax; j-stop can also affect resolution.

- After Perkin-Elmer

- BNL

## Bond Strength and Symmetry

- From J. Mirick, GMU, www.bluelaze.com

- IR activity hinges on change in dipole moment

- Diatomic Hooke’s Law

- ~3650 cm-1

- ~3750 cm-1

- ~1600 cm-1

## Comparatively Routine (but valuable) High Pressure Infrared Measurements

- Pressure shifts of vibrational modes; increases in force constants, changes in anharmonicity, and shifts in bonding.
- Characterizations of phase transitions or shifts in coordination.
- Pressure-induced band gap closure

## Relatively Common High-P Infrared Measurements

- Pressure-induced mode shifts (Bond strength)
- Phase transition-induced mode shifts (Symmetry changes)
- Each are fundamental for monitoring pressure-induced changes in bonding properties, and have macroscopic thermodynamic implications, as well...

- -Mg2SiO4-a high pressure phase

## Temperature Distribution in Earth

- Smooth regions are modulated by the phonon spectrum

- Williams, CMB Monograph, 1998

## The Adiabat

- In most of Earth’s Interior, thermal buoyancy dominates over viscous effects
- Interior is convecting, and near adiabatic
- (T/)ad = T/or ln(T/To) =  ln(/o)
- Thermodynamically,  is V(dP/dE)s, or
- Thermal Expansion/(Compressibility**Heat Capacity)  --> A Measure of Anharmonicity

## , the Grüneisen Parameter and the Geotherm

- , the Grüneisen Parameter and the Geotherm

- can also be shown to equal
- di//(dV/V),
- Where the sum is over the i modes of the crystal.
- So, our understanding of the temperature distribution in the convective portion of the planet(s) hinges on knowing the vibrational spectrum and its volume dependence: thus, lots and lots of determinations of pressure- (and temperature-) induced mode shifts...

## A Subtle Transition in CaCO3-Calcite

- A Subtle Transition in CaCO3-Calcite

- From the left: CO3 asymmetric stretches,
- symmetric stretches, and out-of-plane bend

- Catalli and Williams, Am. Min, 2005.

## Calcite-III IR and X-ray

- Complex, unquenchable structures at high pressure may produce difficult-to-interpret x-ray patterns; diagnostic changes may be observed in vibrations of molecular-like units.
- This phase transition may be between two monoclinic phases.

- Fiquet et al., Am. Min., 1994

- Catalli & Williams, Am. Min., 2005

## Quartz and Silica Glass: A mildly more Exotic Structural Transformation

- And, give or take, most tetrahedral silicates compressed at 300 K seem to look about the same at 30-40+ GPa: the rationale for this remains unclear...

## Band Gap Closure

- 					Cervantes et al., J.P.C.S., 2002

- A different style of IR measurement

## Probably Understudied Phenomena at high P

- Overtones, Combinations
- Reflectance, TO/LO splitting
- Band Gap Closure, Electronic Structure
- High T phases, liquids
- Visible Spectroscopy
- Far-IR spectroscopy

## Advantages of Synchrotron IR for High Pressure Applications

- Microfocus capabilities
- 		Key for laser-heated spots,
- 		Trace constituents (water, etc.)
- Far-infrared intensity
- 		Critical for lattice dynamics; but hard 				w/conventional sources
- Reflectance from high pressure samples
- 		Produces constraints on ionic polarizability, band 		structure

## S. Jacobsen

## A Far-IR example--Muscovite Mica

- K+
- displacement

- Williams, Knittle, Scott, Liu et al.,in prep.

- KAl3Si3O10(OH)2 in a
- layered structure

- K-ions

- Al-Si
- Layer

## Hydroxyl Stretch of Muscovite

- Williams, Knittle, Scott, Liu et al.,in prep.

- A probe of another portion of the structure

## Absorption vs. Reflectance

- From: minerals.gps.caltech.edu

- TO-LO (Transverse Optic-Longitudinal Optic) Splitting--Associated with strongly polarized vibrations/structures. LO appears in reflectance geometry.

- LO    TO

## Reflectance of Ice at High Pressures

- Struzhkin, Goncharov, Hemley, Mao, PRL, 1997

- Documentation of Symmetrization of the O-H-O
- Distance--using reflectance to invert for optical
- constants of water.

## Cascading Resonances in H2O

- Cascading Resonances in H2O

- Struzhkin, Goncharov, Hemley, Mao, PRL, 1997

## Protons at High Pressure in Hydrogen-bonded Systems

- O------H..............................O

## Overtones in Ice

- Splittings, decrease in strength and ultimate disappearance of each overtone...

- Larsen and Williams, PRB, 1998

## Potential Surface of H2O

- Two Born-Mayer plus a Buckingham potential; Pressure-induced Increase in polarizability of oxygen required.

- Larsen and Williams

## Infrared of Melts at High P/T 

- Hampered by large absorption
- Reflectance studies may ultimately prove most useful
- Overtones are useful for strongly bound species
- Thermal emission can be problematic

- O-H Stretch
- + H-O-H Bend

- O-H Stretch
- + O-H Libration

- Sowerby and Keppler, Am. Min., 1999

## Conclusions

- Vibrational spectroscopy remains the most prevalent means by which amorphous materials, or materials difficult to characterize by structural techniques, are characterized at high pressures; from an Earth Sciences perspective, such studies remain in their infancy.
- There has only been limited advantage taken of the unique aspects of  synchrotron-infrared studies: high spatial resolution, far-infrared strength, and high pressure reflectance studies (and, high P time-resolved IR studies are really limited...).
- The future of high-P synchrotron infrared spectroscopy is bright, and NSLS is well poised in this arena...

## Slide 35

## Barrier Height from Overtone Disappearance

- Larsen and Williams

## Probing High-P Melts Quenched in T

- Should ‘lock in’ structure at the temperature of a fast glass transition
- Spatial selectivity could be critical in probing material exposed to different temperatures

- IR Spectrum: (Mg0.9,Fe0.1)SiO3 + 3 wt% H2O,
- Melted at 38.7 GPa and decompressed

- Closmann and Williams, Am. Min.

## Barrier Decrease -> Overtone Annihilation