Polyamorphism and liquid-liquid phase transitions: challenges for experiment and theory

Multiple Melting Temperatures in Glass-Forming Melts

All materials are vitrified by fast quenching even monoatomic substances. Second melting temperatures accompanied by weak exothermic or endothermic heat are often observed at Tn+ after remelting them above the equilibrium thermodynamic melting transition at Tm. These temperatures, Tn+, are due to the breaking of bonds (configurons formation) or antibonds depending on the thermal history, which is explained by using a nonclassical nucleation equation. Their multiple existence in monoatomic elements is now demonstrated by molecular dynamics simulations and still predicted. Proposed equations show that crystallization enthalpy is reduced at the temperature Tx due to new vitrification of noncrystallized parts and their melting at Tn+. These glassy parts, being equal above Tx to singular values or to their sum, are melted at various temperatures Tn+ and attain 100% in Cu46Zr46Al8 and 86.7% in bismuth. These first order transitions at Tn+ are either reversible or irreversible, depending on the formation of super atoms, either solid or liquid.

Folded network and structural transition in molten tin

The fundamental relationships between the structure and properties of liquids are far from being well understood. For instance, the structural origins of many liquid anomalies still remain unclear, but liquid-liquid transitions (LLT) are believed to hold a key. However, experimental demonstrations of LLTs have been rather challenging. Here, we report experimental and theoretical evidence of a second-order-like LLT in molten tin, one which favors a percolating covalent bond network at high temperatures. The observed structural transition originates from the fluctuating metallic/covalent behavior of atomic bonding, and consequently a new paradigm of liquid structure emerges. The liquid structure, described in the form of a folded network, bridges two well-established structural models for disordered systems, i.e., the random packing of hard-spheres and a continuous random network, offering a large structural midground for liquids and glasses. Our findings provide an unparalleled physical picture of the atomic arrangement for a plethora of liquids, shedding light on the thermodynamic and dynamic anomalies of liquids but also entailing far-reaching implications for studying liquid polyamorphism and dynamical transitions in liquids.

Unraveling the structural origin of liquid anomalies remains a challenging topic. Xu et al. propose a folded-network structural model for molten tin and provide insights into the observed second-order-like structural transition.

Liquid structure under extreme conditions: high-pressure x-ray diffraction studies

Under extreme conditions of high pressure and temperature, liquids can undergo substantial structural transformations as their atoms rearrange to minimise energy within a more confined volume. Understanding the structural response of liquids under extreme conditions is important across a variety of disciplines, from fundamental physics and exotic chemistry to materials and planetary science.In situexperiments and atomistic simulations can provide crucial insight into the nature of liquid-liquid phase transitions and the complex phase diagrams and melting relations of high-pressure materials. Structural changes in natural magmas at the high-pressures experienced in deep planetary interiors can have a profound impact on their physical properties, knowledge of which is important to inform geochemical models of magmatic processes. Generating the extreme conditions required to melt samples at high-pressure, whilst simultaneously measuring their liquid structure, is a considerable challenge. The measurement, analysis, and interpretation of structural data is further complicated by the inherent disordered nature of liquids at the atomic-scale. However, recent advances in high-pressure technology mean that liquid diffraction measurements are becoming more routinely feasible at synchrotron facilities around the world. This topical review examines methods for high pressure synchrotron x-ray diffraction of liquids and the wide variety of systems which have been studied by them, from simple liquid metals and their remarkable complex behaviour at high-pressure, to molecular-polymeric liquid-liquid transitions in pnicogen and chalcogen liquids, and density-driven structural transformations in water and silicate melts.

Structure of levitated Si-Ge melts studied by high-energy x-ray diffraction in combination with reverse Monte Carlo simulations

The short-range order in liquid Si, Ge and binary Si_x-Ge_1-xalloys (x= 0.25, 0.50, 0.75) was studied by x-ray diffraction and reverse Monte Carlo simulations. Experiments were performed in the normal and supercooled liquid states by using the containerless technique of aerodynamic levitation with CO₂laser heating, enabling deeper supercooling of liquid Si and Si-Ge alloys than previously reported. The local atomic structure of liquid Si and Ge resembles theβ-tin structure. The first coordination numbers of about 6 for all compositions are found to be independent of temperature indicating the supercooled liquids studied retain this high-density liquid (HDL) structure. However, there is evidence of developing local tetrahedral ordering, as manifested by a shoulder on the right side of the first peak inS(Q) which becomes more prominent with increasing supercooling. This result is potentially indicative of a continuous transition from the stable HDLβ-tin (high pressure) phase, towards a metastable low-density liquid phase, reminiscent of the diamond (ambient pressure) structure.

A new one-site coarse-grained model for water: Bottom-up many-body projected water (BUMPer). II. Temperature transferability and structural properties at low temperature

A number of studies have constructed coarse-grained (CG) models of water to understand its anomalous properties. Most of these properties emerge at low temperatures, and an accurate CG model needs to be applicable to these low-temperature ranges. However, direct use of CG models parameterized from other temperatures, e.g., room temperature, encounters a problem known as transferability, as the CG potential essentially follows the form of the many-body CG free energy function. Therefore, temperature-dependent changes to CG interactions must be accounted for. The collective behavior of water at low temperature is generally a many-body process, which often motivates the use of expensive many-body terms in the CG interactions. To surmount the aforementioned problems, we apply the Bottom-Up Many-Body Projected Water (BUMPer) CG model constructed from Paper I to study the low-temperature behavior of water. We report for the first time that the embedded three-body interaction enables BUMPer, despite its pairwise form, to capture the growth of ice at the ice/water interface with corroborating many-body correlations during the crystal growth. Furthermore, we propose temperature transferable BUMPer models that are indirectly constructed from the free energy decomposition scheme. Changes in CG interactions and corresponding structures are faithfully recapitulated by this framework. We further extend BUMPer to examine its ability to predict the structure, density, and diffusion anomalies by employing an alternative analysis based on structural correlations and pairwise potential forms to predict such anomalies. The presented analysis highlights the existence of these anomalies in the low-temperature regime and overcomes potential transferability problems.

Physical vapor deposition of a polyamorphic system: Triphenyl phosphite

In situ AC nanocalorimetry and dielectric spectroscopy were used to analyze films of vapor-deposited triphenyl phosphite. The goal of this work was to investigate the properties of vapor-deposited glasses of this known polyamorphic system and to determine which liquid is formed when the glass is heated. We find that triphenyl phosphite forms a kinetically stable glass when prepared at substrate temperatures of 0.75-0.95T_g, where T_g is the glass transition temperature. Regardless of the substrate temperature utilized during deposition of triphenyl phosphite, heating a vapor-deposited glass always forms the ordinary supercooled liquid (liquid 1). The identity of liquid 1 was confirmed by both the calorimetric signal and the shape and position of the dielectric spectra. For the purposes of comparison, the glacial phase of triphenyl phosphite (liquid 2) was prepared by the conventional method of annealing liquid 1. We speculate that these new results and previous work on vapor deposition of other polyamorphic systems can be explained by the free surface structure being similar to one polyamorph even in a temperature regime where the other polyamorph is more thermodynamically stable in the bulk.

Polymorphic phase transition in liquid and supercritical carbon dioxide

We present experiments on molecular density fluctuations in liquid and supercritical (SC) CO₂ using small-angle neutron scattering. Thermal density fluctuations in SC-CO₂ determine susceptibility and correlation length identifying the Widom line at their maxima. Droplet formation occurs at the gas–liquid line and between 20 and 60 bar above the Widom line, the corresponding borderline identified as the Frenkel line. The droplets start to form spheres of constant radius of ≈ 45 Å and transform into rods and globules at higher pressure. Droplet formation represents a liquid–liquid (polymorphic) phase transition of the same composition but different density, whose difference defines its order parameter. Polymorphism in CO₂ is a new observation stimulating interesting discussions on the topics of gas-like to liquid-like transition in SC fluids and polymorphism since CO₂ represents a “simple” van der Waals liquid in contrast to water, which is the most widely studied liquid showing polymorphism in its supercooled state.

First-Order Liquid-Liquid Transition without Density Discontinuity in Molten Sodium Acetate Trihydrate and Its Influence on Crystallization

Liquid-liquid transition (LLT) refers to the phase transition among thermodynamically distinct liquid states with identical composition in analogy to the polymorphic transition in solid. The growing awareness of its significance to understanding the nature of liquid also provokes curiosity about its potential impact on crystallization. Here, we report a first-order liquid-liquid transition above liquidus temperature in the melt of sodium acetate trihydrate using nuclear magnetic resonance, differential scanning calorimetry, and high-precision density measurements, which show negligible change in density associated with the observed LLT. Further, the kinetics and products of crystallization are significantly influenced by LLT, providing a new way for the controlling crystallization pathway and realizing crystal polymorph selection.

Is the λ-transition in liquid sulfur a fragile-to-strong transition?

The abrupt and large increase in the viscosity of liquid sulfur above the λ-transition temperature T_λ corresponds to a reversible structural transformation in the form of a ring-to-chain polymerization reaction. The mechanistic connection between this structural transformation and viscosity is investigated by studying the compositional dependence of the shear relaxation behavior of supercooled S_xSe_100-x liquids as their structural evolution mimics that of liquid sulfur across the λ-transition. The results of steady and oscillatory shear parallel-plate rheometry indicate that the viscosity of these liquids is controlled by the S/Se-S/Se bond scission/renewal dynamics and the time scale of these dynamics rapidly increases as the relative concentrations of rings and chains in the structure become comparable. The coexistence of these two types of topological units in these liquids lowers the conformational entropy of the chain elements due to a steric hindrance from the ring elements, resulting in a rapid drop in the fragility as S is added to Se. The same topological effect resulting from the ring-to-chain transformation in liquid S renders the highly fragile molecular liquid below T_λ, a strong polymerized liquid above T_λ. Therefore, it is argued that the λ-transition of liquid S corresponds to a fragile-to-strong liquid-liquid transition.

Bond-counting potentials: A classical many-body model of covalent bonding with exact solutions in one dimension

We introduce "bond-counting" potentials, which provide an elementary description of covalent bonding. These simplistic potentials are intended for studies of the mechanisms behind a variety of phase transitions in elemental melts, including the liquid-liquid phase transitions (LLPTs) in phosphorus and bismuth. As a first study employing such potentials, an analytic solution of a one-dimensional model system is presented, including its thermodynamic properties and its structure factor. In the simplest case, the chemical valency of each atom is 1, and either single atoms or diatomic molecules are present. At low temperatures and moderate pressures, the system consists almost exclusively of molecules, and single atoms act as topological defects. A slightly more complicated case involves a valency of 2, with either single or double bonding. This system exhibits a first-order LLPT from a molecular to a polymeric phase as in phosphorus. In this case, the one-dimensional model system exhibits phase separation for finite-sized systems at low temperatures. A variant of this system also exhibits a nonequilibrium phase transformation upon heating the molecular condensed phase, qualitatively similar to boiling in white phosphorus.

Dynamics on next-neighbour distances in liquid and undercooled gallium

Density fluctuations of liquid and 20 K undercooled gallium have been studied by neutron spectroscopy. The decay of density fluctuations has been recorded at the structure factor maximum over a wide temperature range up to twice the melting temperature. The amplitude of the scattering function falls off with rising temperature in a nonlinear way with a changing slope around [Formula: see text]. The derived generalized longitudinal viscosity shows an upturn with decreasing temperature in the same temperature range. This increase in viscosity can be understood that liquid gallium transforms from a more fluid liquid metal to a more viscous liquid metal in that temperature range upon cooling. The change in the amplitude shows a remarkable agreement with results from liquid aluminium, lead and rubidium. This study suggests a universal crossover in dynamics of liquid monatomic metals, despite the many peculiar properties of gallium.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

The reversibility and first-order nature of liquid-liquid transition in a molecular liquid

Liquid–liquid transition is an intriguing phenomenon in which a liquid transforms into another liquid via the first-order transition. For molecular liquids, however, it always takes place in a supercooled liquid state metastable against crystallization, which has led to a number of serious debates concerning its origin: liquid–liquid transition versus unusual nano-crystal formation. Thus, there have so far been no single example free from such debates, to the best of our knowledge. Here we show experimental evidence that the transition is truly liquid–liquid transition and not nano-crystallization for a molecular liquid, triphenyl phosphite. We kinetically isolate the reverse liquid-liquid transition from glass transition and crystallization with a high heating rate of flash differential scanning calorimetry, and prove the reversibility and first-order nature of liquid–liquid transition. Our finding not only deepens our physical understanding of liquid–liquid transition but may also initiate a phase of its research from both fundamental and applications viewpoints.

The nature of the phenomenon of so-called ‘liquid-liquid transitions' in molecular liquids is a long-standing debate. Here, the authors demonstrate the reversibility and first-order nature of the liquid-liquid transition in triphenyl phosphite via flash differential scanning calorimetry.

Time-Resolved Light Scattering Study on the Kinetics of the Liquid-Liquid Transition in Triphenyl Phosphite

There is experimental evidence suggesting the existence of a liquid-liquid transition (LLT) in a single-component liquid. However, none of this evidence is free from controversy, including the case of a molecular liquid, triphenyl phosphite, which we study here. Furthermore, the kinetics of LLT has been largely unexplored. Here we study the phase-transition dynamics of triphenyl phosphite in a supercooled liquid state by means of time-resolved polarized and depolarized small-angle light scattering to clarify whether the transition is a liquid-liquid transition (LLT) or merely nanocrystal formation. A part of this study was recently reported in another of our papers [Shimizu, R.; Kobayashi, M.; Tanaka, H. Phys. Rev. Lett. 2014, 112, 125702]. A detailed analysis of our experimental results of light scattering and the comparison with heat evolution during LLT have revealed the following facts. The polarized scattering from domains has a finite (nonzero) intensity in the low-wavenumber limit, and the time evolution of its average intensity is almost proportional to the square of the heat-releasing rate. The depolarized scattering intensity monotonically increases in the process of LLT during isothermal annealing above the spinodal temperature TSD but exhibits a peak below TSD. On the basis of these results, we suggest that the primary process is LLT, whose order parameter is of a nonconserved nature, but accompanies nanocrystal formation. In the NG-type LLT, the sharp interface between liquid II droplets and the liquid I matrix promotes nanocrystal formation there, whereas much less nanocrystal formation is induced in the SD-type LLT due to the lack of such sharp interfaces.

Polyamorphism in tetrahedral substances: Similarities between silicon and ice

Tetrahedral substances, such as silicon, water, germanium, and silica, share various unusual phase behaviors. Among them, the so-called polyamorphism, i.e., the existence of more than one amorphous form, has been intensively investigated in the last three decades. In this work, we study the metastable relations between amorphous states of silicon in a wide range of pressures, using Monte Carlo simulations. Our results indicate that the two amorphous forms of silicon at high pressures, the high density amorphous (HDA) and the very high density amorphous (VHDA), can be decompressed from high pressure (∼20 GPa) down to the tensile regime, where both convert into the same low density amorphous. Such behavior is also observed in ice. While at high pressure (∼20 GPa), HDA is less stable than VHDA, at the pressure of 10 GPa both forms exhibit similar stability. On the other hand, at much lower pressure (∼5 GPa), HDA and VHDA are no longer the most stable forms, and, upon isobaric annealing, an even less dense form of amorphous silicon emerges, the expanded high density amorphous, again in close similarity to what occurs in ice.

Thermodynamic properties of liquid gallium from picosecond acoustic velocity measurements

Due to discrepancies in the literature data the thermodynamic properties of liquid gallium are still in debate. Accurate measurements of adiabatic sound velocities as a function of pressure and temperature have been obtained by the combination of laser picosecond acoustics and surface imaging on sample loaded in diamond anvil cell. From these results the thermodynamic parameters of gallium have been extracted by a numerical procedure up to 10 GPa and 570 K. It is demonstrated that a Murnaghan equation of state accounts well for the whole data set since the isothermal bulk modulus BT has been shown to vary linearly with pressure in the whole temperature range. No evidence for a previously reported liquid-liquid transition has been found in the whole pressure and temperature range explored.

Microscopic identification of the order parameter governing liquid-liquid transition in a molecular liquid

A liquid-liquid transition (LLT) in a single-component substance is an unconventional phase transition from one liquid to another. LLT has recently attracted considerable attention because of its fundamental importance in our understanding of the liquid state. To access the order parameter governing LLT from a microscopic viewpoint, here we follow the structural evolution during the LLT of an organic molecular liquid, triphenyl phosphite (TPP), by time-resolved small- and wide-angle X-ray scattering measurements. We find that locally favored clusters, whose characteristic size is a few nanometers, are spontaneously formed and their number density monotonically increases during LLT. This strongly suggests that the order parameter of LLT is the number density of locally favored structures and of nonconserved nature. We also show that the locally favored structures are distinct from the crystal structure and these two types of orderings compete with each other. Thus, our study not only experimentally identifies the structural order parameter governing LLT, but also may settle a long-standing debate on the nature of the transition in TPP, i.e., whether the transition is LLT or merely microcrystal formation.

Flexible confinement leads to multiple relaxation regimes in glassy colloidal liquids

Understanding relaxation of supercooled fluids is a major challenge and confining such systems can lead to bewildering behaviour. Here, we exploit an optically confined colloidal model system in which we use reduced pressure as a control parameter. The dynamics of the system are "Arrhenius" at low and moderate pressure, but at higher pressures relaxation is faster than expected. We associate this faster relaxation with a decrease in density adjacent to the confining boundary due to local ordering in the system enabled by the flexible wall.

Water and water-like liquids: relationships between structure, entropy and mobility

Liquids with very diverse underlying interactions share the thermodynamic and transport anomalies of water, including metalloids, ionic melts and mesoscopic fluids. The generic feature that characterises such water-like liquids is a density-driven shift in the nature of local order in the condensed phases. The key semiquantitative relationships between structural order, thermodynamics and transport that are necessary in order to map out the consequences of this common qualitative feature for liquid-state properties and phase transformations of such systems are reviewed here. The application of these ideas to understand and model tetrahedral liquids, especially water, is discussed and possible extensions to other complex fluids are considered.

First-order liquid-liquid phase transition in cerium

We report the first experimental observation of a liquid-liquid phase transition in the monatomic liquid metal cerium, by means of in situ high-pressure high-temperature x-ray diffraction experiments. At 13 GPa, upon increasing temperature from 1550 to 1900 K high-density liquid transforms to a low-density liquid, with a density difference of 14%. Theoretic models based on ab initio calculations are built to investigate the observed phase behavior of the liquids at various pressures. The results suggest that the transition primarily originates from the delocalization of f electrons and is deemed to be of the first order that terminates at a critical point.

Bond orientational order in liquids: Towards a unified description of water-like anomalies, liquid-liquid transition, glass transition, and crystallization: Bond orientational order in liquids

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.

Poisson's ratio and modern materials

In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by ½ and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt.

The liquid-liquid phase transition in silicon revealed by snapshots of valence electrons

The basis for the anomalies of water is still mysterious. Quite generally tetrahedrally coordinated systems, also silicon, show similar thermodynamic behavior but lack--like water--a thorough explanation. Proposed models--controversially discussed--explain the anomalies as a remainder of a first-order phase transition between high and low density liquid phases, buried deeply in the "no man's land"--a part of the supercooled liquid region where rapid crystallization prohibits any experimental access. Other explanations doubt the existence of the phase transition and its first-order nature. Here, we provide experimental evidence for the first-order-phase transition in silicon. With ultrashort optical pulses of femtosecond duration we instantaneously heat the electronic system of silicon while the atomic structure as defined by the much heavier nuclear system remains initially unchanged. Only on a picosecond time scale the energy is transferred into the atomic lattice providing the energy to drive the phase transitions. With femtosecond X-ray pulses from FLASH, the free-electron laser at Hamburg, we follow the evolution of the valence electronic structure during this process. As the relevant phases are easily distinguishable in their electronic structure, we track how silicon melts into the low-density-liquid phase while a second phase transition into the high-density-liquid phase only occurs after the latent heat for the first-order phase transition has been transferred to the atomic structure. Proving the existence of the liquid-liquid phase transition in silicon, the hypothesized liquid-liquid scenario for water is strongly supported.

Low-density to high-density transition in Ce75Al23Si2 metallic glass

Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce(75)Al(23)Si(2) metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T(x)) between them with a turning point at about 2 GPa. Compared with Ce(75)Al(25) metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T(x) and changes their slopes dT(x)/dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

Surface-wetting effects on the liquid-liquid transition of a single-component molecular liquid

Even a single-component liquid may have more than two liquid states. The transition between them is called a 'liquid–liquid transition' (LLT). Such LLTs have recently attracted considerable attention mainly because of the fundamental interest in the physical origin of this counter-intuitive phenomenon. In this study, we report the first observation of wetting effects on LLT for a molecular liquid, triphenyl phosphite. We find a transition from partial to complete wetting for nucleation-growth-type LLT when approaching the spinodal temperature of LLT. Some features unique to LLT are also revealed, reflecting for example the non-conserved nature of its order parameter. We also find that the wetting behaviour is not induced by dispersion forces, but by weak hydrogen bonding to a solid substrate, implying its important role in the LLT itself. Using wetting effects may open a new possibility to control kinetics and spatial patterns of nucleation-growth-type LLT.

A phase transition between two liquid states is a counterintuitive phenomenon, but one that is known to happen in certain materials. Murata and Tanaka now show in tryphenyl phosphite that this can also produce a change in the wetting of a surface, from partial to complete, at the transition temperature.

Liquid-liquid phase transition in supercooled yttria-alumina

The structure and thermal characteristics of aerodynamically levitated samples of yttria-alumina in the liquid, supercooled liquid and solid phases were explored in an extensive series of high energy x-ray diffraction, small angle neutron scattering, and pyrometric cooling measurements. Particular focus was placed on the compound (Y2O3)(x)(Al2O3)(1-x) with x = 0.2 for which a liquid-liquid phase transition at a temperature of 1788 K has recently been reported. No structural or thermal signature in support of this metastable phase transition could be found.