amorphous materials at high pressure

Amorphous materialsAmorphous materials at high pressure at high pressure

Chrystèle Sanloup

CSEC, University of Edinburgh, UKCSEC, University of Edinburgh, UKUniversité Pierre et Marie CurieUniversité Pierre et Marie Curie

Institut de Physique du Globe de Paris, France Institut de Physique du Globe de Paris, France

Not thermodynamically stable state choose appropriate -P-T paths

N.B.: confusion or identification of amorphous forms and quenched liquids (glasses) cf. example of S upon decompression

High pressure amorphs - SynthesisHigh pressure amorphs - Synthesis

▪ Pressure-induced amorphization (PIA) ▪ Amorphous-amorphous transitions (AAT)

▪ Opal (amorphous SiO2) - SEM image

Basic unit = nanoscale grains short-order range

Electron microscopy: Best characterization of amorphous materials but not available at HP, and can high-pressure amorphs be quenched ?

Amorphous materialsAmorphous materials

Gaillou et al., Am. Min. 2008

Characterizaton of amorphs at high PCharacterizaton of amorphs at high P

I- Loss of long-range order Diffuse scattering (X-rays and neutrons)

! Except for heavy elements, X-ray criteria for PIA=disappearance of peaks(misleading)

Fujii et al. JPC:SSP 1985 Luo et al. PRB 1993SnI4Sulfur

Structure unrelated to that of the liquid phase at P0


a-CO2

Santoro et al., Nature 2006.

Gregoryanz et al., JCP 2007.

a-N

I- Diffuse X-ray scattering:


Sanloup et al., PRL 2008

amorphous Sulfur

! Very high background/signal ratio




Boehler-Almax anvils

▪ Problems at high P: 1- limited Q-range 2- background substraction

- Empty cell pattern- Crystalline pattern

▪ Advantages of low T: homogeneous samples


II- Density/volumetric measurements

Deplacement of a piston in a cylinderEx: PIA of ice Mishima Nature 1984

Large volume decrease: ~20%

-PIA large volume reduction importance of density measurements on am.

Isample = I0 ∙exp(−diadiatdia−samplesampletsample)

3 unknowns need 3 equations/measurements measurements up to 60 GPa

Sato & Funamori, Rev. Sci. Instr. 2008.


II- Density/volumetric measurements - Radiographic techniques

Liu et al, PNAS 2008.

Up to 10 GPaSe: heavy element

Kaplow et al., Phys. Rev. 1965.

)()()( QIQIQI incohsampcoh 1)(lim QSQ

max

0

)sin(1)(2

1)(4)(Q

drQrQSQrgrrF

, normalization factor such as

Access to:-: initial slope- local structure

2)(

)()(

Qf

QIQS coh


II- Density measurements - X-ray diffraction technique

Characteristics of HP amorphsCharacteristics of HP amorphs

▪ Crystal-like properties: local structure

H2O

Strongly peaked diffraction patterns

Sulfur

-ZrW2O8 amorphous

Keen et al. PRL 2007

IINS (inelastic incoherent neutron scattering)

Similarity of LDA and Ice Ih

Tse Nature 1999


▪ Crystal-like properties: phonon density of states


▪ Crystal-like properties: density

Daisenberg et al., PRB 2007.

Compressibility similar to that of the crystalline counter-part

Sulfur

Silicon

a-CO2

Simple molecular systems: COSimple molecular systems: CO22, N, N22

High T: molecular to non-molecular transition high-energy barrier

Low T: molecular crystal to amorphous form transition

a-N

Gregoryanz et al. PRB 2001, JCP 2007

Goncharov et al. PRL 2000


a-CO2


a-CO2

↑P: PIA, CO2-VI like a-CO2

↓P: AAT, CO2-V like→ CO2-III like a-CO2

↓P: re-crystallization into CO2-I

▪ Amorphous-amorphous transition:

Simple molecular systems: COSimple molecular systems: CO22, N, N22

VI

Simple molecular systems: SSimple molecular systems: S88

631521

112

611

Recrystallisation: a-S → S-III

PIA is the precursor of the phase transition to the high-P polymorph

CN=15.0+/-0.4

CN=16.1+/-0.1

AAT in conjunction with S-III → S-IV transition, rather 1st order transition


Large volume collapse upon PIA

AAT : Low-density amorph (LDA) High-density amorph (HDA)

▪ AAT upon decompression:

2nd order transition: LDA → liquid-like a-S

Re-crystallization at 0.25 GPa-room T into S-I


▪ Crossing of the metastable extension of the melting line

Cold Cold vsvs mechanical melting mechanical melting

Mishima et al., Nature 1984.

PIA

Tse et al., Nature 1999.Mishima, Nature 1996.

Case of H2O

Hemley et al., Nature 1988.

▪ Crossing of the metastable extension of the melting line


Case of SiO2

Crystalline structures collapse regardless of their melting behavior

Amorphization systematically connected with crystal-crystal transformation just above the

amorphisation T.

Brazhkin et al. JNCS 1997


▪ Arguing for mechanical melting: elastic instabilities evidenced before PIA

Phonon softening in Ice Ih PIA predicted at 2.5 GPa


Violation of Born criteria

Gregoryanz et al. PRL 2000

Case of SiO2

Strässle et al. PRL 2004

Case of H2O

NB: P of PIA by mechanical melting always overestimated by Born criteria

B3=(C11-C12)∙C44-2C142

S-I 16 GPa – 175 K S-I 41 GPa – 175 K (just before amorphization)

Role of defectsRole of defects

▪ Defective X-ray patterns upon approaching PIA

Case of sulfur

▪ P-induced reduction of Nb2O5 : Simultaneous amorphization at 19 GPa-300K Reduction O defects in the lattice

▪ Numerical simulations:- defect-free: no transformation until mechanical limit is reached- sample with one vacancy: transformation starts at lower P

G’=(C11-C12)/2-P

Role of defectsRole of defects

Serghiou et al., PRL 1992.

Defects can destabilize the lattice at pressures much lower than the instability pressure.

Bustingorry and Jagla, PRB 2005.

ConclusionsConclusions

▪ PIA occurs if a parent phase is compressed beyond its thermodynamic stability field

▪ Occurs generally at low T: lack of thermal energy not enough atomic mobility for the crystalline-crystalline transition to occur

▪ PIA is the precursor of the phase transition to the high-P polymorph high-P amorphs have crystal-like properties (distinct from glasses)

▪ PIA is accompanied by a large volume reduction

▪ a large variety of materials transform into amorphs at high P

▪ high-P amorphs may undergo 1st or 2nd order AAT

▪ high-P amorphs are often difficult to recover at ambient conditions

▪ Industry of polymers: improved kinetic stability, enhanced mechanical properties

Yu et al., APL, 2009

ConclusionsConclusions

▪ Use of high P to synthesize high quality quenched amorphs

Ivashchenko et al. PRB 2007

Nanocrystalline Siparticle size: 2.2 nm

Nanocrystalline S-III X-ray amorphous: If particle size ~ 10 Å

i.e. ~ 3 crystallographic cells

Scherrer equation:

Particle size=K

w1/2 cos(

Bustingorry and Jagla PRB 2005

Platelets of the high-P phase nucleate on the vacancyBut growth inhibited very small crystal size

a-S 54 GPa

Crystalline S-III

Nanocrystalline S-III?

X-ray amorphs or nanocrystallites ?X-ray amorphs or nanocrystallites ?

LDA and HDA forms have cristalline-like properties (except for complex H2O).

HDA (water) can not be assimilated to a supercooled liquid,Neither LDA/HDA transition to a 2-state liquids (i.e. liquid-liquid transition)by way of csqce

Tse:

Differences between high P amorph and glasses

Amorph-amorph transitionsAmorph-amorph transitions

First evidenced in aSi and a-Ge? (Shimomura Philos Mag 1974 29 p547?),AAT tend to be 1st order transitions (Si, S, H2O?)

confusion or identification of amorphous forms and quenched liquids (glasses) cf. example of S upon decompression

Mishima et al., Nature 1985

2- T increase: High-density amorphous ice (HDA)→Low-density amorphous ice (LDA)

1- Pressure-induced amorphization

3- P increase:LDA→HDA

LDAHDA

Amorphous-amorphous transitionsAmorphous-amorphous transitions

Case of H2O

Klotz et al., PRL 2005

Neutron diffraction data (see D>>)But different picture given by X-rays (see O>>)

N.B.: very complex H2O phase diagram!!!

▪ HDA water: - continuous structural changes towards close-packing - may re-crystallize into different phases

Amorph-amorph transitionsAmorph-amorph transitions

▪ HDA-LDA: 1st order transition ?

Boehler-Almax anvils

430 1010)(lim

T

BQ K

TkQS

Additional constraint at very high pressures:

Negligeable on the expal pattern

• Pb 2: the higher the pressure, the more difficult it is to get the background properly

• Pb 1: limited Q-range:

Amorphous sulphurAmorphous sulphur

Tse Nature 1999

Liquid water

Amorphous HDA

Add P-T phase diagram(cf Klotz)Add PIA paths

Strassle PRL 2007


Case of simple molecular systems:Systematic PIA from molecular to non molecular at low T (not at high T)Recovery of the amorph down to low P (N, Eremets, us with S)

Case of tetraedrally coordinated systems (classical case)

Case of Si, Ge, III-IV compounds and their solid solutions, etc Tsuji et al., Brazhkin et al.: PIA upon DECOMPRESSION from METALLIC state.

Tsuji JNCS 1996

1- Semi-conductor zincblende structure

2- Incr.P: metallic -tin structure

3- decr.P: amorphization, T-dependant

Meade and Jeanloz, PRB 1987

Cr-emulsion mask (1mm lines) on a SiO2-glass

Hemley et al., Nature 1988

Amorphization is thermodynamically induced

But glass not amorphous silica !


Differences between high P amorph and glasses

Deb et al., Nature 414, 528 (2001)

Pressure-induced amorphization of Si (porous Si)

Decompression: HDA→LDA transition(Raman spectroscopy)

Check that the LDA curve goes on the HAD(which then coincides with Si-V)

How was LDA formed? Real PIA or Si gel?

Daisenberg et al., PRB 2007

Transition predicted at 13.7 GPa,Between 14 and 16 GPa experimentally

Brazhkin et al. JNCS 1997

Ultrasonic measurements

Arguing for mechanical melting: elastic instabilities evidenced before PIA

Phonon softening in Ice IhSträssle et al. PRL 2004

PIA predicted at 2.5 GPa


Case of H2O

Brief statement on Born criteria

high P amorphs have cristalline-like properties (cf Tse PRB 2005 et aS).

- Similar thermal conductivity (H2O, Johari PRB2004)

- memory of the initial crystallographic orientation or anisotropy of the amorph: single crystal → amorph (incr.P) → single crystal (decr. P) with same orientation (cf AlPO4, Kruger and Jeanloz 1990 or Brillouin scattering on AlPO4 by Polian PRL1993 and a-SiO2 by McNeil PRL1992)


Case of simple molecular systems:Systematic PIA from molecular to non molecular at low T (not at high T)Recovery of the amorph down to low P (N, Eremets, us with S)

Case of tetraedrally coordinated systems (classical case)

Case of Si, Ge, III-IV compounds and their solid solutions, etc Tsuji et al., Brazhkin et al.: PIA upon DECOMPRESSION from METALLIC state.But also case of S (cf Wilson, from trigonal state, in the Z. Crist. Paper?)

Tsuji: There are two methodsto obtain amorphous materials using high pressure.One is amorphization above the thermodynamic transitionpressure Pt, [1,2] and the other is amorphizationfrom the quenched high-pressure phase below Pt

High pressure amorphsHigh pressure amorphs

-Interests: synthesis of new materials (properties?), In particular through high P polyamorphism

Amorphous (industrial interests?)

-Theoretical interests:- discussion of polyamorphic transitions, 1st vs 2nd order- amorphs taken as proxies for liquids and the search for 2nd critical points- mechanisms of PIA?

High pressure amorphs - InterestsHigh pressure amorphs - Interests


II- Density/volumetric measurements

Strain/gauge technique: limited to <10 GPa but very high precision (0.15%)

Brazhkin et al., JETP 89, 244 (2009)

Tsiok et al., HPR 10, 523 (1992)

g(r)

r

1

0

• I(2) S(Q), structure factor

• S(Q) g(r), radial distribution fonction

sin4

exp)(

2)(

20

QdQfAI

IQS

dQrQQSQnr

rg sin12

11)(

02

with

Amorphous materialsAmorphous materials

▪ No long-range order diffuse X-ray scattering

amorphous materials at high pressure

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