Presentation on theme: "Amorphous materials at high pressure"— Presentation transcript:
1 Amorphous materials at high pressure Chrystèle SanloupCSEC, University of Edinburgh, UKUniversité Pierre et Marie CurieInstitut de Physique du Globe de Paris, France
2 High pressure amorphs - Synthesis ▪ Pressure-induced amorphization (PIA)▪ Amorphous-amorphous transitions (AAT)Mention traditional synthesis of amorphous materials: ultra-fast quenching, chemical vapor deposition, destructive methods such as irradiation (including in natural conditions) or ball-milling.Amorphization upon P-release (but still at high P): apparently known since much earlier (Ringwood, CaSiO3 perovskite decompressed from 10GPa EPSL1975,Tsuji JNCS 1992)Not thermodynamically stable state choose appropriate c-P-T pathsN.B.: confusion or identification of amorphous forms and quenched liquids (glasses)cf. example of S upon decompression
3 Basic unit = nanoscale grains Amorphous materials▪ Opal (amorphous SiO2) - SEM imageBasic unit = nanoscale grains short-order rangeGaillou et al., Am. Min. 2008Electron microscopy:Best characterization of amorphous materials but not available at HP,and can high-pressure amorphs be quenched ?
4 Characterizaton of amorphs at high P I- Loss of long-range order Diffuse scattering (X-rays and neutrons)SulfurSnI4Luo et al. PRB 1993Fujii et al. JPC:SSP 1985! Except for heavy elements,X-ray criteria for PIA=disappearance of peaks(misleading) Structure unrelated to that of the liquid phase at P0
5 Characterizaton of amorphs at high P I- Diffuse X-ray scattering:a-CO2a-NGregoryanz et al., JCP 2007.Santoro et al., Nature 2006.
6 Characterizaton of amorphs at high P I- Diffuse X-ray scattering:amorphous Sulfur! Very high background/signal ratioSanloup et al., PRL 2008
7 Characterizaton of amorphs at high P I- Diffuse X-ray scattering:▪ Problems at high P:1- limited Q-range2- background substractionBoehler-Almax anvils- Empty cell pattern- Crystalline pattern▪ Advantages of low T: homogeneous samples
8 Characterizaton of amorphs at high P II- Density/volumetric measurementsDeplacement of a piston in a cylinderEx: PIA of iceMishima Nature 1984Large volume decrease: ~20%PIA large volume reduction importance of density measurements on am.
9 Characterizaton of amorphs at high P II- Density/volumetric measurements - Radiographic techniquesLiu et al, PNAS 2008.Sato & Funamori, Rev. Sci. InstrMicrotomography: precision claimed= 0.45%, measurements up to 10 GPaSato&Funamori: precision claimed=0.5 % at the highest PIsample = I0 ∙exp(−mdiardiatdia−msamplersampletsample)3 unknownsneed 3 equations/measurementsmeasurements up to 60 GPaUp to 10 GPaSe: heavy element
10 Characterizaton of amorphs at high P II- Density measurements - X-ray diffraction techniquea, normalization factor such asKaplow et al., Phys. RevAccess to:- r: initial slope- local structure
11 Characteristics of HP amorphs ▪ Crystal-like properties: local structureStrongly peaked diffraction patternsSulfurH2Oa-ZrW2O8amorphousZrW2O8=zirconium tungstateVega et al. Monte Carlo simulationsTulk et al., X-ray g(r)ZRW2O8: neutron+Xrays+reverse Monte CarloKeen et al. PRL 2007
12 Characteristics of HP amorphs ▪ Crystal-like properties: phonon density of statesTse Nature 1999IINS (inelastic incoherent neutron scattering) Similarity of LDA and Ice IhDifferences with hyperquenched water
13 Characteristics of HP amorphs ▪ Crystal-like properties: densityDaisenberg et al., PRB 2007.SiliconHAD Si and Si-IISulfur Compressibility similar to that of the crystalline counter-part
14 Simple molecular systems: CO2, N2 Goncharov et al. PRL 2000Gregoryanz et al. PRB 2001, JCP 2007Santoro et al., Nature 2006.a-CO2a-NN: further recrystallization in cg (upon heating, Eremets 2001)aN discovered by Gonchi, very large hysteresis on decompression (Eremets 2001)V-CO2: quartz-like (tetrahedral configuration)High T: molecular to non-molecular transition high-energy barrierLow T: molecular crystal to amorphous form transition
15 Simple molecular systems: CO2, N2 ▪ Amorphous-amorphous transition:a-CO2VIa-CO2↑P: PIA, CO2-VI like a-CO2↓P: AAT, CO2-V like→ CO2-III like a-CO2↓P: re-crystallization into CO2-ISantoro et al., Nature 2006.
16 Simple molecular systems: S8 631521112611Recrystallisation: a-S → S-III PIA is the precursor of the phase transition to the high-P polymorph
17 Simple molecular systems: S8 CN=15.0+/-0.4CN=16.1+/-0.1LDA is semiconducting (IR measurements); SIII is?SI is an insulatorSIV is metallic Large volume collapse upon PIA AAT in conjunction with S-III → S-IV transition, rather 1st order transition AAT : Low-density amorph (LDA) High-density amorph (HDA)
19 Simple molecular systems: S8 ▪ AAT upon decompression: 2nd order transition: LDA → liquid-like a-SRe-crystallization at 0.25 GPa-room T into S-I
20 Cold vs mechanical melting ▪ Crossing of the metastable extension of the melting lineCase of H2ODashed line: extrapolated melting curve (by Mishima)Tse et al: arrow=crossing of the 2 mechanismsThe Lindemann criteria suggests that the onset of an instability is caused when the displacements of atoms exceed a certain threshold, usually a fraction of the interatomic distances.PIATse et al., Nature 1999.Mishima et al., Nature 1984.Mishima, Nature 1996.
21 Cold vs mechanical melting ▪ Crossing of the metastable extension of the melting lineCase of SiO2Hemley et al., Nature 1988.
22 Cold vs mechanical melting Amorphization systematically connected with crystal-crystal transformation just above the amorphisation T. Crystalline structures collapse regardlessof their melting behaviorSi et Ge ont points de cristallisation et de fusion a T plus elevees que GaSbOr c’est le contraire pour T amorphisation (id Hemley et melting curve of SiO2) => Pas logique avec cold meltingBrazhkin et al. JNCS 1997
23 Cold vs mechanical melting ▪ Arguing for mechanical melting: elastic instabilities evidenced before PIA Violation of Born criteriaSträssle et al. PRL 2004Case of H2OCase of SiO2Gregoryanz et al. PRL 2000B3 C11 2 C12C44 2 2C214 . 0Strassle: needs to be fitted by a model to extract elastic parameters and get C11-C12Brazhkin: ! softening is expected to be the most important on the Brillouin zone boundary while ultrasonic measurements registered the behavior of long-wave phonons.Brazhkin: At least 20% softening of the ½(C11-C12) constantB3=(C11-C12)∙C44-2C142Phonon softening in Ice Ih PIA predicted at 2.5 GPaNB: P of PIA by mechanical melting always overestimated by Born criteria
24 Role of defects ▪ Defective X-ray patterns upon approaching PIA Case of sulfurS-I 41 GPa – 175 K(just before amorphization)S-I 16 GPa – 175 K
25 Role of defects ▪ P-induced reduction of Nb2O5 : Serghiou et al., PRL 1992.▪ P-induced reduction of Nb2O5 :Simultaneous amorphization at 19 GPa-300KReduction O defects in the latticeBustingorry and Jagla, PRB 2005.G’=(C11-C12)/2-P▪ Numerical simulations:defect-free: no transformation untilmechanical limit is reached- sample with one vacancy: transformation starts at lower PFecht Nature 1992: when the defect concentration in a cristal reaches aCritical value, it collapses in a disordered state due to DGv (v:vacancy)Serghiou: By analogy with ambient P reduction, authors propose that amorph formed by O defects in the lattice (through shear deformation, Crystallographic Shear Plane) Defects can destabilize the lattice at pressures much lowerthan the instability pressure.
26 Conclusions▪ a large variety of materials transform into amorphs at high P▪ 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 accompanied by a large volume reductionNot only tetrahedral frameworks▪ PIA is the precursor of the phase transition to the high-P polymorphhigh-P amorphs have crystal-like properties (distinct from glasses)▪ high-P amorphs may undergo 1st or 2nd order AAT▪ high-P amorphs are often difficult to recover at ambient conditions
27 Conclusions▪ Use of high P to synthesize high quality quenched amorphsYu et al., APL, 2009High quality quench amorphs: without any crystalMechanical properties: pliability, stretchingTranslucenceChalcogenide alloys: optical (DVD) and electronic (PCM) applications rely on the fast and reversible phase change between the crystalline and amorphous phase induced by heating either via laser irradiation (DVD) or the Joule effect (PCM). Caravati et al. PRL 2009.▪ Industry of polymers:improved kinetic stability, enhanced mechanical properties
29 X-ray amorphs or nanocrystallites ? a-S 54 GPaCrystalline S-IIINanocrystalline S-III?X-ray amorphs or nanocrystallites ?Ivashchenko et al. PRB 2007Nanocrystalline Siparticle size: 2.2 nmScherrer equation:Particle size=Klw1/2 cos(q)Nanocrystalline S-III X-ray amorphous:If particle size ~ 10 Åi.e. ~ 3 crystallographic cellsBustingorry and Jagla PRB 2005Platelets of the high-P phase nucleate on the vacancyBut growth inhibited very small crystal size
30 Amorph-amorph transitions First evidenced in aSi and a-Ge? (Shimomura Philos Mag p547?),AAT tend to be 1st order transitions (Si, S, H2O?)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 csqceTse:Differences between high P amorph and glassesconfusion or identification of amorphous forms and quenched liquids (glasses)cf. example of S upon decompression
31 Amorphous-amorphous transitions Case of H2O2- T increase:High-density amorphous ice (HDA)→Low-density amorphous ice (LDA)HDALDA3- P increase:LDA→HDA1- Pressure-inducedamorphizationMishima et al., Nature 1985
32 Amorph-amorph transitions ▪ HDA-LDA: 1st order transition ?Klotz et al., PRL 2005Neutron diffraction data (see D>>)But different picture given by X-rays (see O>>)very complex phase diagram!!! No wonder every team gets a different picture.LDA/HDA: not good proxy for LDL/HDL transition since high-P amorphs have crystalline-like properties▪ HDA water:- continuous structural changes towards close-packing- may re-crystallize into different phasesN.B.: very complex H2O phase diagram!!!
33 Amorphous sulphur Pb 1: limited Q-range: Boehler-Almax anvils Pb 2: the higher the pressure, the more difficult it is to get the background properlyAdditional constraint at very high pressures: Negligeable on the expal pattern
34 Cold vs mechanical melting Add P-T phase diagram(cf Klotz)Add PIA pathsTse Nature 1999Liquid waterAmorphous HDAStrassle PRL 2007
35 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.1- Semi-conductorzincblende structure2- Incr.P: metallic b-tin structureTsuji JNCS 19963- decr.P: amorphization,T-dependant
36 Characterizaton of amorphs at high P Hemley et al., Nature 1988Meade and Jeanloz, PRB 1987Cr-emulsion mask (1mm lines) on a SiO2-glassBut glass not amorphous silica !Differences betweenhigh P amorph and glassesAmorphization is thermodynamically induced
37 Pressure-induced amorphization of Si (porous Si) Decompression: HDA→LDA transition(Raman spectroscopy)Deb et al., Nature 414, 528 (2001)
38 Check that the LDA curve goes on the HAD Daisenberg et al., PRB 2007Check that the LDA curve goes on the HAD(which then coincides with Si-V)How was LDA formed? Real PIA or Si gel?Transition predicted at 13.7 GPa,Between 14 and 16 GPa experimentally
40 Cold vs mechanical melting Arguing for mechanical melting: elastic instabilities evidenced before PIABrief statement on Born criteriaCase of H2OStrassle: needs to be fitted by a model to extract elastic parameters and get C11-C12Brazhkin: ! softening is expected to be the most important on the Brillouin zone boundary while ultrasonic measurements registered the behavior of long-wave phonons.Brazhkin: At least 20% softening of the ½(C11-C12) constantBrazhkin et al. JNCS 1997Ultrasonic measurementsPhonon softening in Ice IhSträssle et al. PRL 2004 PIA predicted at 2.5 GPa
41 Characteristics of HP amorphs 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)
42 High pressure amorphs 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
43 High pressure amorphs - Interests Interests: synthesis of new materials (properties?),In particular through high P polyamorphismAmorphous (industrial interests?)Theoretical interests:discussion of polyamorphic transitions, 1st vs 2nd orderamorphs taken as proxies for liquids and the search for 2nd critical pointsmechanisms of PIA?
44 Characterizaton of amorphs at high P II- Density/volumetric measurementsStrain/gauge technique: limited to <10 GPa but very high precision (0.15%)Tsiok et al., HPR 10, 523 (1992)Brazhkin et al., JETP 89, 244 (2009)
45 ▪ No long-range order diffuse X-ray scattering Amorphous materials▪ No long-range order diffuse X-ray scatteringg(r)r1I(2) S(Q), structure factorS(Q) g(r), radial distribution fonctionwith