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![Synchrotron radiation arrangements for in situ structural studies of high temperature supercooled liquids. (a) Schematic of laser-heated aerodynamic levitator (b) The SAXS/WAXS/video arrangement used on station MPW 6.2 at the Synchrotron Radiation Source [33].](profile/Martin-Wilding-2/publication/222186826/figure/fig2/AS:776559526936576@1562157627108/Synchrotron-radiation-arrangements-for-in-situ-structural-studies-of-high-temperature.png)
Synchrotron radiation arrangements for in situ structural studies of high temperature supercooled liquids. (a) Schematic of laser-heated aerodynamic levitator (b) The SAXS/WAXS/video arrangement used on station MPW 6.2 at the Synchrotron Radiation Source [33].
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![Fig. 1. Two state model [11,12] and the development of liquid-liquid...](profile/Martin-Wilding-2/publication/222186826/figure/fig1/AS:776559526948864@1562157627031/Two-state-model-11-12-and-the-development-of-liquid-liquid-and-amorphous-amorphous_Q320.jpg)
Employing small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) combined with laser-heated aerodynamic levitation has enabled different transitions in supercooled yttrium oxide–aluminium oxide to be distinguished. These include liquid–liquid phase transitions as well as high temperature crystallization for different composition...
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... samples for levitation were prepared by melting weighed mixtures of high purity Y 2 O 3 and Al 2 O 3 in a laser hearth [36]. Spheroids approximately 2 mm in diameter were then remelted for the X-ray experiments in the levitator furnace illustrated schematically in Fig. 2(a). Compositions AY15, AY20 and AY25 were chosen alongside Al 2 O 3 in order to search for liquid-liquid transitions in situ at temperatures much higher than had been possible in previous ex situ studies [17][18][19][20][21][22][23][27][28][29]. Adopting these alumina-rich compositions also meant that full conversion of HDL to LDL might ...
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... these alumina-rich compositions also meant that full conversion of HDL to LDL might be expected, as intimated in Ref. [17]. Target compositions were accurate to within 0.5 wt% before melting and remained so after several hours at the high temperatures needed for in situ sequences of SAXS/WAXS measurements of reliable quality to be obtained. Fig. 2(b) shows how the levitator furnace and video camera [35] were adapted for the SAXS/WAXS geometry [34]. Within the levitator furnace the high temperature drop is supported by drag forces from a vertical stream of argon [31,35] and is heated with a CO 2 laser as shown in Fig. 2(a). With top down heating the vertical temperature drop DT ...
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... sequences of SAXS/WAXS measurements of reliable quality to be obtained. Fig. 2(b) shows how the levitator furnace and video camera [35] were adapted for the SAXS/WAXS geometry [34]. Within the levitator furnace the high temperature drop is supported by drag forces from a vertical stream of argon [31,35] and is heated with a CO 2 laser as shown in Fig. 2(a). With top down heating the vertical temperature drop DT is around 50 K [23,29]. The levitated drop is aligned with focused monochromatic X-rays and the diffracted (WAXS) and scattered (SAXS) fans are detected with multiwire gas proportion counters using Ar/Xe mixtures using RAPID2 readout electronics [33]. SAXS and WAXS detectors were ...
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... drop was continuously monitored with a high resolution video camera. This also enabled changes in the vertical height of the drop with the gas nozzle to be checked. Precise vertical alignment of the spherical specimen with respect to the incoming focused X-ray beam was achieved by maintaining constant transmission using I o and I T ion chambers (Fig. 2(a)). Data collection extended over 2 min, during which time the pyrometer indicated that temperature of the levitated drop was stable to within a few degrees ...
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... recent studies [23,28,29,35]. In addition very rapid quench rates are needed (400-500 K/s) in order to achieve polyamorphic phase separation and to avoid early crystallization i.e. where with normal cooling T LL < T cryst for these compositions (Fig. 4(c)). This may be possible for 0.5 mm diameter drops with the in situ techniques described here (Fig. 2) if microfocused X-rays can be employed. Levitated smaller drops might then quench sufficiently rapidly from the liquidus to reach the lower T LL temperatures for yttria-rich compositions by overshooting T cryst . For compositions around AY20, though, Fig. 4(c) demonstrates that under steady supercooled conditions T LL > T cryst , in ...
Citations
... This is partly because the coexistence of high-density amorphous (HDA) and low-density amorphous (LDA) phases with the same composition was claimed based on liquid-liquid phase transition in the undercooled melt in the 1990s. 54,[120][121][122][123] Diffraction studies and MD simulations of Y 2 O 3 -Al 2 O 3 glasses have revealed that AlO 4 tetrahedra networks constitute the frame of glass and that the framework is unaffected by the composition change in the narrow glassforming range. 124,125) The averaged oxygen coordination number of Al was estimated to be 4.5, implying a significant amount of highly coordinated Al other than AlO 4 . ...
... mol% Y 2 O 3 by aerodynamic levitation or in an iridium wire furnace (Tangeman et al., 2004;Skinner et al., 2008;Nasikas et al., 2011). YA glasses and their melts have been the subject of numerous studies due to the possible existence of polyamorphism in this system (Wilding and McMillan, 2001;Wilding et al., 2002a,b;Wilding and McMillan, 2002;McMillan et al., 2003;Tangeman et al., 2004;Weber et al., 2004;McMillan and Wilding, 2008;Skinner et al., 2008;Greaves et al., 2008;Barnes et al., 2009;Greaves et al., 2009;Nasikas et al., 2011). Aasland and McMillan (1994) have observed the coexistence of two glassy states of identical composition but different structures, densities and thermodynamic properties (Fig. 9). ...
... The two HDA-LDA states imply a density-driven phase separation that could underline a first-order liquid-liquid phase transition. However the occurrence of this polyamorphism has been strongly debated (Greaves et al., 2008;Barnes et al., 2009;Greaves et al., 2009). Structural studies, using 27 Al and 89 Y NMR, Raman and diffraction, have been conducted mainly on Y 2 O 3 -Al 2 O 3 and La 2 O 3 -Al 2 O 3 glasses among RE 2 O 3 -Al 2 O 3 glasses (Florian et al., 2001;Wilding et al., 2002a,b;Wilding and McMillan, 2002;McMillan et al., 2003;Weber et al., 2004;Tangeman et al., 2004;Nasikas et al., 2011;Watanabe et al., 2020), supported by MD simulations (McMillan et al., 2007;Du and René Corrales, 2007;Cristiglio et al., 2007;Du et al., 2009). ...
... MD simulations confirm that changes in the Y-Y correlations is the main difference between HDA and LDA configurations (McMillan et al., 2003). Furthermore, dynamic density fluctuations have been evidenced in MD simulations (McMillan et al., 2007), confirming experimental indication of unmixing of high and low density liquids at the nanoscale that underlines a liquidliquid phase transition (Greaves et al., 2008(Greaves et al., , 2009. ...
Aluminosilicate glasses are of great importance for industrial applications and are good analogs of magmas. In practical applications, almost all silicate glasses incorporate alumina either as impurity or as a large component and Al2O3 usually imparts greater chemical durability, viscosity, glass transformation temperatures, improves mechanical properties, reduces devitrification tendencies and thermal expansion. Recent experimental and modeling techniques have substantially improved our understanding of the atomic-scale structure, providing a strong basis to better control glass properties. In this article, the composition-structure-property relationships in a great variety of glasses containing Al2O3 are reviewed.
... mol% Y 2 O 3 by aerodynamic levitation or in an iridium wire furnace (Tangeman et al., 2004;Skinner et al., 2008;Nasikas et al., 2011). YA glasses and their melts have been the subject of numerous studies due to the possible existence of polyamorphism in this system (Wilding and McMillan, 2001;Wilding et al., 2002a,b;Wilding and McMillan, 2002;McMillan et al., 2003;Tangeman et al., 2004;Weber et al., 2004;McMillan and Wilding, 2008;Skinner et al., 2008;Greaves et al., 2008;Barnes et al., 2009;Greaves et al., 2009;Nasikas et al., 2011). Aasland and McMillan (1994) have observed the coexistence of two glassy states of identical composition but different structures, densities and thermodynamic properties (Fig. 9). ...
... The two HDA-LDA states imply a density-driven phase separation that could underline a first-order liquid-liquid phase transition. However the occurrence of this polyamorphism has been strongly debated (Greaves et al., 2008;Barnes et al., 2009;Greaves et al., 2009). Structural studies, using 27 Al and 89 Y NMR, Raman and diffraction, have been conducted mainly on Y 2 O 3 -Al 2 O 3 and La 2 O 3 -Al 2 O 3 glasses among RE 2 O 3 -Al 2 O 3 glasses (Florian et al., 2001;Wilding et al., 2002a,b;Wilding and McMillan, 2002;McMillan et al., 2003;Weber et al., 2004;Tangeman et al., 2004;Nasikas et al., 2011;Watanabe et al., 2020), supported by MD simulations (McMillan et al., 2007;Du and René Corrales, 2007;Cristiglio et al., 2007;Du et al., 2009). ...
... MD simulations confirm that changes in the Y-Y correlations is the main difference between HDA and LDA configurations (McMillan et al., 2003). Furthermore, dynamic density fluctuations have been evidenced in MD simulations (McMillan et al., 2007), confirming experimental indication of unmixing of high and low density liquids at the nanoscale that underlines a liquidliquid phase transition (Greaves et al., 2008(Greaves et al., , 2009. ...
... The follow-up studies on various physical quantities, including the structural and vibrational properties, supported this claim. [256][257][258][259][260][261][262] However, there have been criticisms on this claim 263,264 and debates on its nature. 265,266 One is the common problem of multicomponent systems: When we observe the coexistence of the two liquid or amorphous phases, the critical point is whether the composition is the same or different between them. ...
Two or more liquid states may exist even for single-component substances, which is known as liquid polymorphism, and the transition between them is called liquid–liquid transition (LLT). On the other hand, the existence of two or more amorphous states is called polyamorphism, and the transition between them is called amorphous–amorphous transition (AAT). Recently, we have accumulated a lot of experimental and numerical evidence for LLT and AAT. These intriguing phenomena provide crucial information on the fundamental nature of liquid and amorphous states. Here, we review the recent progress in this field and discuss how we can physically rationalize the existence of two or more liquids (glasses) for a single-component substance. We also discuss the relationship between liquid-, amorphous-, and crystal-polymorphisms, putting a particular focus on the roles of thermodynamics, mechanics, and kinetics.
... Soon after the first simulations indicating an LLT in water, Aasland and McMillan [2] presented experimental results which puported coexistance of two liquid states of identical composition at temperatures around T g in Yttria-Alumina [(YO) x -(AlO) 1−x ]. Later, high-temperature experiments in the Yttria-Alumina liquid [169,170] found evidence of nanoscale fluctuations in the form of a rise in S(k) at low k which they probed with x-ray diffraction. Barnes et al. [24] investigated these findings with high energy x-ray diffraction, small angle neutron scattering, and pyrometric cooling measurements for [(YO) 20 -(AlO) 80 ]. ...
Amorphous solids, or glasses, are distinguished from crystalline solids by
their lack of long-range structural order. At the level of two-body structural
correlations, glassformers show no qualitative change upon vitrifying from a
supercooled liquid. Nonetheless the dynamical properties of a glass are so much
slower that it appears to take on the properties of a solid. While many
theories of the glass transition focus on dynamical quantities, a solid's
resistance to flow is often viewed as a consequence of its structure. Here we
address the viewpoint that this remains the case for a glass. Recent
developments using higher-order measures show a clear emergence of structure
upon dynamical arrest in a variety of glass formers and offer the tantalising
hope of a structural mechanism for arrest. However a rigorous fundamental
identification of such a causal link between structure and arrest remains
elusive. We undertake a critical survey of this work in experiments, computer
simulation and theory and discuss what might strengthen the link between
structure and dynamical arrest. We move on to highlight the relationship
between crystallisation and glass-forming ability made possible by this deeper
understanding of the structure of the liquid state, and emphasize the potential
to design materials with optimal glassforming and crystallisation ability, for
applications such as phase-change memory. We then consider aspects of the
phenomenology of glassy systems where structural measures have yet to make a
large impact, such as polyamorphism (the existence of multiple liquid states),
aging (the time-evolution of non-equilibrium materials below their glass
transition) and the response of glassy materials to external fields such as
shear.
... LLT was also reported in yttriaalumina. 121,122,[153][154][155] However, there are also still on-going debates on the composition range over which this phenomenon occurs and the experimental conditions required to observe it 156 and even on its existence itself. 157 For molecular liquids, Mishima et al. found an amorphous-amorphous transition in water. ...
Liquids are often assumed to be homogeneous and isotropic at any lengthscale and translationally invariant. The standard liquid-state theory is constructed on the basis of this picture and thus basically described in terms of the two-body density correlation. This picture is certainly valid at rather high temperatures, where a liquid is in a highly disordered state. However, it may not necessarily be valid at low temperatures or for a system which has strong directional bonding. Indeed, there remain fundamental unsolved problems in liquid science, which are difficult to explain by such a theory. They include water's thermodynamic and kinetic anomalies, liquid-liquid transitions, liquid-glass transitions, and liquid-solid transitions. We argue that for the physical description of these phenomena it is crucial to take into account many-body (orientational) correlations, which have been overlooked in the conventional liquid-state theory. It is essential to recognise that a liquid can lower its free energy by local or mesoscopic ordering without breaking global symmetry. Since such ordering must involve at least a central particle and its neighbours, which are more than two particles, it is intrinsically a consequence of many-body correlations. Particularly important ordering is associated with local breakdown of rotational symmetry, i.e., bond orientational ordering. We emphasize that translational ordering is global whereas orientational ordering can be local. Because of the strong first-order nature of translational ordering, its growth in a liquid state is modest. Thus any structural ordering in a liquid should be associated primarily with orientational ordering and not with translational ordering. We show that bond orientational ordering indeed plays a significant role in all the above-mentioned phenomena at least for (quasi-)single-component liquids. In this Introductory Lecture, we discuss how these phenomena can be explained by such local or mesoscopic ordering in a unified manner.
... This allows the region over which LLPT appear to be studied. By placing the levitated drop within an X-ray or neutron beam enables small-and wide-angle scattering patterns to be measured in situ [153] at fixed T , or during controlled versus free cooling to ambient conditions [114,152,[154][155][156][157][158][159][160]. ...
... Indeed, such an electron density contrast recorded by backscattered electron imaging was the first indication used by Aasland and McMillan to ascertain the difference in mass density between the two glassy polymorphs [57]. In situ isothermal experiments conducted on levitated AYx liquids by Greaves et al. revealed a dramatic rise in SAXS intensity heralding the onset of the LLTP (Fig. 12) [155,159,161]. By comparison single phase liquids like alumina that show no such unmixing phenomena prior to crystallization display only the expected gradual increase in the thermal background as the temperature rises and density fluctuations increase in magnitude [157,159]. ...
... By comparison single phase liquids like alumina that show no such unmixing phenomena prior to crystallization display only the expected gradual increase in the thermal background as the temperature rises and density fluctuations increase in magnitude [157,159]. Wide angle X-ray scattering (WAXS) data collected simultaneously with the SAXS measurements [155,161] reveal complementary changes occurring in the atomic structure. At lower temperatures the micrometer-scale segregation of HDL and LDL phases evolves with the LDL phase floating to the top of the levitating drop. ...
... In the case of first order LLPT encountered as a function of the density, as observed for liquid phosphorous or Y 2 O 3 -Al 2 O 3 supercooled liquids [48][49][50][51][52][53][54], an energy barrier between regions of configurational energy space appears to extend well above the main features of the CEL such that the liquid system itself experiences a transition as the P and T are varied. When amorphous materials are prepared by routes including condensation from a vapor phase, or by chemical means such as decomposition or polymerization reactions, the underlying CEL for the system is expected to remain constant as the possible interatomic configurations and their contributions to the potential energy are the same, but the various minima and amorphous basins will be sampled and populated differently, and they may be connected by different pathways, compared with those for a corresponding thermal glass. ...
... Subsequent studies using a range of calorimetric, spectroscopic and high energy X-ray and neutron scattering techniques support the presence of distinguishable LDA and HDA forms of the Al 2 O 3 -Y 2 O 3 glasses [112,[287][288][289][290] and polarizable ion MD studies carried out during cooling the simulated liquids indicated the onset of density fluctuations as the temperature was lowered [112,291,292]. More recently, these results have been supported by in situ X-ray scattering studies on levitated liquids that show clear evidence for the occurrence of the LLPT for certain compositions in the supercooled regime [50,51]. Weber et al. [293] have reproduced similar polyamorphic glassy textures over a more extended compositional range that includes the technologically important YAG (Y 3 Al 5 O 12 ; 37.5 mol% Y 2 O 3 ) composition. ...
... Recent studies of refractory liquids including Y 2 O 3 -Al 2 O 3 have focused on in situ investigations of the stable and supercooled regimes using containerless levitation techniques combined with smalland wide-angle X-ray (SAXS, WAXS) and neutron scattering. Greaves et al. [50,51] reported a maximum in the SAXS signal that corresponded to a shift in the position and height of the first peak in the diffraction pattern, interpreted as a density fluctuation occurring on a nanometer scale prior to formation of the LDL liquid. This maximum occurred at 1788 K, consistent with calorimetric data [289,290]. ...
Pressure-induced amorphization (PIA) is a phenomenon that involves an abrupt transition between a crystalline material and an amorphous solid through application of pressure at temperatures well below the melting point or glass transition range. Amorphous states can be produced by PIA for substances that do not normally form glasses by thermal quenching. It was first reported for ice Ih in 1984 following prediction of a metastable melting event associated with the negative initial melting slope observed for that material. The unusual phenomenon attracted intense interest and by the early 1990’s PIA had been reported to occur among a wide range of elements and compounds. However, with the advent of powerful experimental techniques including high resolution synchrotron X-ray and neutron scattering combined with more precise control over the pressurization environment, closer examination showed that some of the effects previously reported as PIA were likely due to formation of nanocrystals, or even that PIA was completely bypassed during examination of single crystals or materials treated under more hydrostatic compression conditions. Now it is important to understand these results together with related discussions of polyamorphic behavior to gain better understanding and control over these metastable transformations occurring in the low temperature range where structural relaxation and equilibration processes are severely constrained. The results will lead to useful new high-density amorphous materials or nanocrystalline composites containing metastable crystalline varieties and the experiments have driven new theoretical approaches to modeling the phenomena. Here we review the incidence and current understanding of PIA along with related phenomena of density- and entropy-driven liquid-liquid phase transitions (LLPT) and polyamorphism. We extend the discussion to include polymeric macromolecules and biologically-related materials, where the phenomena can be correlated with reversible vs irreversible unfolding and other metastable structural transformations.
... The existence of LLT in liquid Si was also suggested by high-pressure experiments [144,145,147] and numerical simulations [139,141,142], but the presence of LLT still needs to be checked carefully. LLT was also reported in yttria-alumina [146,156,147,157,158]. However, there are also still on-going debates on the composition range over which this phenomenon occurs and the experimental conditions required to produce the effect [159] and even on its existence itself [160]. ...
... As in the case of water, K T may also exhibit an anomalous increase, due to the increase in the number density of locally favoured structures, S, itself (not due to its fluctuations). Finally, it is worth noting that critical-like fluctuations and the steep increase in the susceptibility, which might be due to LLT, were recently reported for supercooled yttria-alumina melts [157,158,201,202]. ...
There are at least three fundamental states of matter, depending upon temperature and pressure: gas, liquid, and solid (crystal). These states are separated by first-order phase transitions between them. In both gas and liquid phases a complete translational and rotational symmetry exist, whereas in a solid phase both symmetries are broken. In intermediate phases between liquid and solid, which include liquid crystal and plastic crystal phases, only one of the two symmetries is preserved. Among the fundamental states of matter, the liquid state is the most poorly understood. We argue that it is crucial for a better understanding of liquids to recognize that a liquid generally has the tendency to have a local structural order and its presence is intrinsic and universal to any liquid. Such structural ordering is a consequence of many-body correlations, more specifically, bond angle correlations, which we believe are crucial for the description of the liquid state. We show that this physical picture may naturally explain difficult unsolved problems associated with the liquid state, such as anomalies of water-type liquids (water, Si, Ge, ...), liquid-liquid transition, liquid-glass transition, crystallization and quasicrystal formation, in a unified manner. In other words, we need a new order parameter representing a low local free-energy configuration, which is a bond orientational order parameter in many cases, in addition to a density order parameter for the physical description of these phenomena. Here we review our two-order-parameter model of liquid and consider how transient local structural ordering is linked to all of the above-mentioned phenomena. The relationship between these phenomena is also discussed.
... Concurrently to the beamline electromagnetic levitation (BEML) development, Krishnan et al. [19] performed X-ray scattering experiments on aerodynamically levitated droplets. ADL devices were further coupled with small angle and anomalous X-ray scattering [43,44], X-ray absorption spectroscopy [45], and neutron scattering techniques [46,47]. Advances in using ADL (CNL) at synchrotron and neutron sources were recently reviewed by Hennet et al. [48]. ...
... The X-ray diffraction during levitation has been applied to the rare-earth oxides and other refractory oxides, which were intensively studied both with regard to their shortrange order [44,102,103] and crystallization peculiarities [43,45,52,104,105]. Nagashio et al. [52] have determined formation of the metastable hexagonal phase during solidification of undercooled YFeO 3 and LuFeO 3 melts. ...
Until recently understanding the solidification
behavior of high temperature materials, including many
intermetallic systems, required evaluation of a great number
of individual solidification experimental results. An
additional challenge was the reactivity of metallic melts at
elevated temperatures. Alternative methods for in situ
observation of solidification processes using the highenergy
synchrotron X-ray diffraction, which came up in the
last decade, are reviewed in the present work. Here,
solidifying phases and transformation sequences are
directly related to their X-ray diffraction pattern, which
avoids any confusion caused by subsequent phase transformations especially in complex systems. By containerless processing with aerodynamic, electrostatic and electromagnetic levitation methods, adapted to the application at the synchrotron beamline, contamination of the melt with impurities is avoided, which can corrupt the results of solidification studies by conventional methods. To date, the
majority of the studies is focused on metastable phase
formation and the structure of undercooled melts. Current
efforts on liquid–solid phase transformations under conditions
close to the equilibrium, which provide a great potential for acquisition of phase diagram data of refractory and reactive alloys, are also addressed.
