Raman spectroscopy at high pressure and temperature for the study of Earth's mantle and planetary minerals

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1 Raman spectroscopy at high pressure and temperature for the study of Earth's mantle and planetary minerals Bruno Reynard, Gilles Montagnac, and Hervé Cardon Laboratoire de Géologie de Lyon

2 Coupling HP and HT to Raman

3 High temperatures Daniel et al 1995

4 Sample Ruby 100 µm ruby fluorescence P=0 P=10 GPa wavenumber (cm -1 )

5 thermocouple

6 Intnesity spectrum of thermal emission T wavelength IR laser

7 Gillet 1993 Gillet et al 1993

8 Pressure measurements Ruby fluorescence: up to 150 GPa Other fluorescent sensors Goncharov et al 1985 Raman sensors Diamond peak up to 400 GPa How to choose? Substance that has an incompressibility (or bulk modulus) close to the pressure range you are studying

9 c b Goncharov et al 1985 Convenient because you do not need to add another material in the experimental chamber

10 High temperatures Daniel et al 1995

11 High temperatures

12 High temperatures Anorthite liquid Daniel et al 1995

13 High temperatures Pulsed-laser gated-detector system BN up to 2300 K Exarhos and Schaaf 1991

14 High temperatures

15 Why do HP-HT Raman? Follow structural transformations of materials Probe the interaction potential of the crystal Define P-T calibrants for DAC cell Calculate thermodynamic properties Relate it to geophysical issues high-pressure phases in Earth phase transformations in meteorites fossil pressure

16 Upper mantle Olivine : (Mg,Fe) 2 SiO 4 Pyroxene : (Ca,Mg,Fe)SiO 3 Garnet : (Ca,Mg,Fe) 3 (Al,Fe) 2 Si 3 O 12 Transition zone β-(mg,fe) 2 SiO 4 γ-(mg,fe) 2 SiO 4 (Mg,Fe)SiO 3 -ilmenite Majoritic garnet Lower mantle (Mg,Fe)SiO 3 -perovskite (Mg,Fe)O ferropericlase CaSiO 3 -perovskite The high-pressure phases of the transition zone and lower mantle are inferred from experiments, minerals observed in shock vein melts of chondritic meteorites and inclusions in diamonds

17 NWA2737 (Diderot) Dunite with homogeneous olivine Fo 79 T= C, fo 2 FMQ

18 Raman spectroscopy (010) (100) Raman intensity (arbitrary units) clear stripe dark zone dark zone [001] Wavenumber (cm -1 ) Van de Moortele et al. AM 2007ab Mg 2 SiO 4 Durben et al. AM 1993 Mg 2 GeO 4 Reynard et al. PCM 1994

19 Paleostress Mineral inclusion Izreali et al 1999 Diamond host Raman shift of the diamond line because of residual pressure in the inclusions 0.7 cm -1 = 1 GPa along <100>, 2.2 cm -1 along <111> Olivine 5-6 cm -1 = 1 GPa

20 Lattice potentials and vibrational levels crystal = harmonic oscillator k Vibrational energy E n = (n ) h" P n = e"e n / k B T U vib = N # e "E i / k B T i= 0 " i P i E i " = 2 1!! k Force constant Reduced mass; E Δm/mm

21 Lattice potentials and vibrational levels Anharmonicity e.g. Morse potential " e = 1 2# k e µ a = k e 2D e ( ) # " 2 e E n /hc = " e n +1/2 ( ) 2 4D e n +1/2

22 Lattice potentials and vibrational levels " e = 1 2# k e µ a = k e 2D e ( ) # " 2 e E n /hc = " e n +1/2 ( ) 2 4D e n +1/2 u i = hcω i /k B T, x i = ω i /4D e ( s "/ s)# f anh = % i ( ) /( 1$ exp($ u i " ) 1$ 2 " u i " exp $ u i "/ 2+ x i " u i "/ 4 u i exp ( $u i / 2+ x i u i / 4) / 1$ exp($u i ) [ x i u i " exp ( $ u ") /( 1$ exp($ u " ) 2 ] i i [ ] ( ) 1$ 2x i u i exp ( $u i ) /( 1$ exp($u i ) 2 Bigeleisen and Mayer 1947; Urey 1947

23 Lattice potentials and vibrational levels Varying P and T allows exploring the potential parameters and their variations with volume

24 A case study Mg 2 GeO 4 Olivine analogue to forsterite Modes soften with T and harden with P

25 Mode anharmonicity Vibrational frequencies ν i (P,T 0 ) and ν i (P 0,T) Anharmonic parameters extrinsic (volume dependent) γ it = -( lnν i / lnv) Tamb = K T ( lnν i / P) Tamb + % ln("(p 0,T )) qh = ln("(p 0,T 0 )) - - #/q ', & ( ) (( V (P 0,T )/V (P 0,T 0 ))) q $1 (. * ) 0 / γ ip = -( lnν i / lnv) Pamb = -1/α ( lnν i / T) Pamb intrinsic (volume independent) a i = ( lnν i / T) V m i = ( lna i / lnv) T

26 Mode anharmonicity Vibrational frequencies ν i (P,T) Anharmonic parameters extrinsic (volume dependent) γ it = -( lnν i / lnv) Tamb = K T ( lnν i / P) Tamb γ ip = -( lnν i / lnv) Pamb = -1/α ( lnν i / T) Pamb intrinsic (volume independent) a i = ( lnν i / T) V m i = ( lna i / lnv) T Small quantities difficult to measure

27 Intrinsic anharmonic parameters ln("(p 0,T )) measured - ln("(p 0,T )) qh = $ a i dt = #" th T m T 0

28 THERMODYNAMIC MODELLING Vibrational frequencies ν i (P,T) Anharmonic parameters γ it = -( lnν i / lnv) Tamb = K T ( lnν i / P) Tamb γ ip = -( lnν i / lnv) Pamb = -1/α ( lnν i / T) Pamb a i = ( lnν i / T) V m i = ( lna i / lnv) T ) # F vib = h! 2 +k B Tln 1"exp "h! / + % % ( k B T ( +ak B T2. g(!)d! * + $ * # & -,! % P th = T h" V 2 + h" ( % # # exp% h" ( ) mak B T 2 / 0, / g (")d" % & ( & V, % )1( ( / + $ $ $ k B T ' ' '. # $ && '', -.

29 Carbonates stability at high P and T Computed thermodynamic properties of magnesite MgCO 3 at low pressures

30 THERMODYNAMIC MODELLING Raman spectroscopy gives a very partial sample of the vibrational density of states, no account of the dispersion in the Brillouin zone It is necessary to couple Raman and first-principles calculations for prediction of thermodynamics, phase diagrams, isotopic fractionation,

31 Intrinsic anharmonic parameters ln("(p 0,T )) measured - ln("(p 0,T )) qh = $ a i dt = #" th T m T 0 a i = constant m i = 0 ) # F vib = h! 2 +k B Tln 1"exp "h! / + % % ( k B T ( +ak B T2. g(!)d! * + $ * # & -,! % P th = T h" V 2 + h" ( % # # exp% h" ( ) mak B T 2 / 0, / g (")d" % & ( & V, % )1( ( / + $ $ $ k B T ' ' '. # $ && '' Intrinsic anharmonicity No contribution to V(P,T) Contribution to free energy, -.

32 Phase transitions 1st and 2nd order I n t e n s i t y ( a. u ) Wavenumbers (cm -1 ) c s q z c s c s q z c s c s Quartz Coesite quenched 300 K ~ 900 K Quartz Heating of quartz at 7 GPa p r o g r e s s i v e h e a t i n g Raman Shift (cm -1 ) SiO 2

33 Kingma et al. Nature 1995 Stishovite

34 Second-order phase transition

35 Critical softening at high order Elastic softening of orthopyroxenes above 600 C phase transition Low frequency Raman modes that derive from acoustic modes

36 Critical softening at high order phase transition Softening of orthopyroxene Raman modes assigned to transition from Pnma to Cmcm

37 Metastable transformations Mg 2 GeO 4 Reynard et al 1994 Richet and Gillet 1997 Ge-O-Ge bonds Densified silica glass PIA Relevant to shock transformations in meteorites

38 Mirror effects of P and T Heating of HP phase at room P SiO 4 monomers Olivine Low P glass SiO 3 chains! MgSiO 3 ilmenite Si 2 O 7 dimers Wadsleyite

39 Should we keep doing Raman spectroscopy on solids at HP and HT? Murakami et al 2007

40 Should we keep doing Raman spectroscopy on solids at HP and HT? Murakami et al 2007

41 Why not Easy to use technique exploratory experiment before synchrotron runs or before using a more cumbersome technique (Brillouin, ) Coupling with first-principles calculation necessary Raman data provide a benchmark for extending predictions of elastic, thermodynamic and transport properties (thermal conductivity) Complex systems (fluids, melts, )

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