Metastable Crystals Research Articles

In Operando Analysis of Cathode Reaction By Synchrotron X-Ray Absorption and Diffraction

1. Introduction in operando analysis enables us to observe non-equilibrium behavior occurring in an operating battery condition without touching its components and so actual processes associated with charging/discharging can be elucidated. In this study, in operando techniques are applied to investigate two phenomena; (1) non-equilibrium phase transition behavior (2) stability at electrode / electrolyte interface. 2. Snapshot Observation of Phase Transition Dynamics in LiFePO4 and LiNi0.5Mn1.5O4 [1-4] Phase transitions of solid state materials are widely utilized in lithium-ion batteries (LIBs). Phase transitions are explained using a phase diagram with physicochemical parameters, e.g. concentration and temperature. Phase diagrams, including the stability of phase transitions, are explained using the concept of Gibbs-energy, based on the equilibrium between stable phases on either side of a phase transition. For phase transitions in practical devices such as LIBs, the actual phase transition takes place under non-equilibrium conditions, which can result in phenomena different to those expected from thermodynamics. The difficulty in in situ analysis has been low time resolutions. Recently the measuring probes have been much improved and observation at practical charging/discharging rate to 50 C is now available. In this study, in situ techniques by using synchrotron X-ray method and its application to lithium battery analysis using their measurement characteristics are demonstrated.The phase transition between LiFePO4 and FePO4 under non-equilibrium battery operation was tracked in real-time using time-resolved X-ray diffraction. A metastable crystal phase appears in conjunction with increasing current density, in addition to the thermodynamically stable LiFePO4 and FePO4 phases. The metastable phase gradually diminishes under open circuit conditions following electrochemical cycling. We propose a phase transition path that passes through the metastable phase, and posit the new phase’s role in decreasing nucleation energy, accounting for the excellent rate capability of LiFePO4. We examined LiNi0.5Mn1.5O4 as another example. It has been known that there are two phase transitions in its charging processes, namely LiNi0.5Mn1.5O4 (Li1) to Li0.5Ni0.5Mn1.5O4 (Li0.5) and Li0.5 to Ni0.5Mn1.5O4 (Li0). In the in situ measurement, it turned out that the Li0.5 phase is clearly observed during charging and is obscure during discharging, showing the thermodynamically reversible but kinetically asymmetric behavior. Using potential step experiments and kinetic analysis, this phenomenon is ascribed to the slow phase transition between Li0.5 and Li0, compared to that between Li1 and Li0.5. The high time resolution was effective in data acquisition during the potential step experiments. 3. in operando X-ray Absorption Spectroscopic Study on Stability at Electrode / Electrolyte Interface [5-7] In the previously proposed deterioration mechanisms of LIBs, the electrode/electrolyte interface is thought to play a significant role. For example, the formation of a solid electrolyte interface, changes in the crystal structure on the surface of active materials during Li ion extraction/insertion, and improvement in the cyclic performance through surface coating of the active materials have all been reported previously. However, determining the specific cause of the interface stability is quite difficult because the geometric and electronic structures must be tracked with a resolution of less than a few nanometers to reveal the phenomena at the electrode/electrolyte interface. To achieve further elucidation of the deterioration mechanism of LIBs, clarification of the electronic structure at the electrode/electrolyte interface under operation conditions is required.We investigated the effects of the electronic structure at the electrode/electrolyte interface on the cyclic performance of cathode materials via in-situ total-reflection fluorescence X-ray absorption spectroscopy. In a LiCoO2 thin-film electrode that exhibits gradual deterioration upon subsequent Li ion extractions and insertions (cycling), the reduction of Co ions at the electrode/electrolyte interface was observed upon immersion in an organic electrolyte followed by irreversible behavior after cycling. In contrast, in a LiFePO4 thin-film electrode, the electronic structure at the electrode/electrolyte interface was stable and reversible upon electrolyte immersion with subsequent cycling. The increased stability of the electronic structure at the LiFePO4/electrolyte interface impacts its cycling performance. Acknowledgement This work was supported by RISING battery project from NEDO, Japan.

Fabrication of Barium Titanate Based Ferroelectrics by Containerless Processing

Lead-free ferroelectric materials are desired in our lives owing to the environmental problem, and are anticipated to replace conventional ferroelectrics such as Pb(Zr,Ti)O3(PZT) ceramics. Many researchers have attempted to develop lead-free ceramics whose ferroelectric properties would surpass those of PZT ceramics. Recently, it has been reported that oxygen-deficient hexagonal-BaTiO3which is metastable state of perovskite-BaTiO3exhibits giant dielectric constants over the wide temperature range. Such a metastable material has capability as a lead-free dielectric material with high performance. The containerless processing has an advantage over the other conventional methods in synthesizing metastable materials. It can suppress heterogeneous nucleation from the container wall, and produce the undercooled state below the solidification point of the metastable phase, which is lower than that of the stable phase. The purpose of this study is to synthesize barium titanate based ferroelectrics by the containerless processing as lead-free metastable materials. We developed the aerodynamic levitation furnace which enables us to levitate and melt a sample about 1-3 mm in diameter in containerless condition. Figure 1 shows a schematic view of the aerodynamic levitation furnace. The samples are levitated by the gas jet nozzle, and are melted using the CO2laser radiation. The metastable crystals of the barium titanate based ferroelectrics were fabricated by the aerodynamic levitation furnace. The crystal structure is demonstrated by analyzing high energy synchrotron radiation powder diffraction data. We discuss the prospects of the ferroelectricity on the basis of the determined crystal structure.

Effects of Formulation and Process Factors on the Crystal Structure of Freeze-Dried Myo-Inositol

The objective of this study was to elucidate effects of formulation and process variables on the physical forms of freeze-dried myo-inositol. Physical properties of myo-inositol in frozen solutions, freeze-dried solids, and cooled heat-melt solids were characterized by powder X-ray diffraction (PXRD), thermal analysis (differential scanning calorimetry [DSC] and thermogravimetric), and simultaneous PXRD-DSC analysis. Cooling of heat-melt myo-inositol produced two forms of metastable anhydrate crystals that change to stable form (melting point 225 °C-228 °C) with transition exotherms at around 123 °C and 181 °C, respectively. Freeze-drying of single-solute aqueous myo-inositol solutions after rapid cooling induced crystallization of myo-inositol as metastable anhydrate (transition at 80 °C-125 °C) during secondary drying segment. Contrarily, postfreeze heat treatment (i.e., annealing) induced crystallization of myo-inositol dihydrate. Removal of the crystallization water during the secondary drying produced the stable-form myo-inositol anhydrate crystal. Shelf-ramp slow cooling of myo-inositol solutions resulted in the stable and metastable anhydrous crystal solids depending on the solute concentrations and the solution volumes. Colyophilization with phosphate buffer retained myo-inositol in the amorphous state. Crystallization in different process segments varies crystal form of freeze-dried myo-inositol solids.

Metastable growth of pure wurtzite InGaAs microstructures.

III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals.

Photoactive β-Bi2O3 architectures prepared by a simple solution crystallization method

Metastable tetragonal bismuth oxide (β-Bi2O3) architectures of pumpkin shape were successfully prepared by a solution crystallization technique, which was performed at 70°C without further calcination or other complex treatment. The elementary units of β-Bi2O3 architectures are microrods of ~1μm in width. The metastable crystalline structure was determined by X-ray powder diffraction (XRD), and the crystal evolution process from irregular particles to pumpkin aggregates was investigated on a field emission scanning electron microscope (FESEM). The tetragonal β-Bi2O3 crystalline powders exhibited orange in color, which could transform to yellow monocline α-Bi2O3 crystals upon enough reaction time as 60min, the corresponding morphology changes from pumpkin structure of β-Bi2O3 crystals to big diamond structure of α-Bi2O3 crystals. The stabilization of metastable β-Bi2O3 crystals in the solution system is a size controlled process. By tuning experimental parameters, such as NaOH concentration, reaction temperature, stirring rate etc., metastable β-Bi2O3 crystals can preserve stably in the reaction system for different time. The pumpkin β-Bi2O3 architectures showed excellent photocatalytic activity to Rhodamine B (RhB) degradation under visible light irradiation, which is due to an indirect dye photosensitization degradation process.

Rate Induced Solubility and Suppression of the First-Order Phase Transition in Olivine LiFePO4

Electrode phase transitions are of large practical importance in Li-ion batteries determining the voltage profile and as a decisive factor in the transition kinetics. In particular in LiFePO4 the impact of defects, particle size, and charge rate on the phase transition in LiFePO4, has been studied intensively. The end-member phases, lithium-rich triphilyte Li1- bFePO4 (LFP) and lithium-poor heterosite LiaFePO4 (FP), demonstrate narrow solid-solution domains however both phase field modelling and DFT predict that the first-order phase transition can be suppressed by applying high rates leading to a solid-solution transition1-3 giving a rationale for the intrinsically fast kinetics of the LiFePO4 material Recent in-situ high-rate diffraction studies by Orikasa et al.4 , 5 revealed a metastable Lix ∼ 0.6FePO4 phase in addition to the thermodynamically stable LiFePO4 and FePO4 phases rather than the predicted solid-solution transformation1-3.To determine the phase transition mechanism dependence on the dis(charge) rate we performed an in-situ synchrotron diffraction study with (dis)charge rates ranging from a very low rate of C/5 up to ultra-high rates of 60C. At C/5 charging diffraction shows the established first-order phase transition that occurs upon delithiating LiFePO4. With increasing charging rate the LiFePO4 and FePO4reflections increasingly shift indicating lattice parameters associated with increasing solubility in both end members. In addition with increasing charge rates considerable diffracted intensity is observed between the Bragg reflections indicating that a fraction of the material undergoes a solid solution transformation bypassing the first-order phase transition.At the early stages of charging the metastable phase reported by Orisaka et al.4 , 5 is observed which can be explained based on the phase diagram of LiFePO4. The distribution in environments observed at high rates, including the charged FePO4 the distribution of LixFePO4 phases and the non-reacted LiFePO4 at high rates indicates that the transformation moves through the electrode as a transformation wave, revealing that improvement of electrode performance should focus on optimization the ionic/electronic transport in LiFePO4electrodes rather than on lowering nucleation barriers. These results challenge theorists to capture the observed non-equilibrium thermodynamics of this material.1 Malik, R., Zhou, F. & Ceder, G. Kinetics of non-equilibrium lithium incorporation in LiFePO(4). Nature Materials 10, 587-590, doi:10.1038/nmat3065 (2012).2 Bai, P., Cogswell, D. A. & Bazant, M. Z. Suppression of Phase Separation in LiFePO4 Nanoparticles During Battery Discharge. Nano Letters 11, 4890-4896, doi:10.1021/nl202764f (2011).3 Cogswell, D. A. & Bazant, M. Z. Coherency Strain and the Kinetics of Phase Separation in LiFePO4 Nanoparticles. Acs Nano 6, 2215-2225, doi:10.1021/nn204177u (2012).4 Orikasa, Y. et al. Direct Observation of a Metastable Crystal Phase of LixFePO4 under Electrochemical Phase Transition. Journal of the American Chemical Society 135, 5497-5500, doi:10.1021/ja312527x (2013).5 Orikasa, Y. et al. Transient Phase Change in Two Phase Reaction between LiFePO4 and FePO4 under Battery Operation. Chemistry of Materials 25, 1032-1039, doi:10.1021/cm303411t (2013).

Superdiffusive cusp-like waves in the mercuric iodide precipitate system and their transition to regular reaction bands.

We report a two-dimensional (2D) reaction-diffusion system that exhibits a superdiffusive propagating wave with anomalous cusp-like contours. This wave results from a leading precipitation reaction (wavefront) and a trailing redissolution (waveback) between initially separated mercuric chloride and potassium iodide to produce mercuric iodide precipitate (HgI2) in a thin sheet of a solid hydrogel (agar) medium. The propagation dynamics is accompanied by continuous polymorphic transformations between the metastable yellow crystals and the stable red crystals of HgI2. We study the dynamics of wavefront and waveback propagation that reveals interesting anomalous superdiffusive behavior without the influence of external enhancement. We find that a transition from superdiffusive to subdiffusive dynamics occurs as a function of outer iodide concentration. Inner mercuric concentrations lead to the transition from the anomalous cusp-like to cusp-free regular bands. While gel concentration affects the speed of propagation of the wave, it has no effect on its shape or on its superdiffusive dynamics. Microscopically, we show that the macroscopic wave propagation and polymorphic transformations are accompanied by an Ostwald ripening mechanism in which larger red HgI2 crystals are formed at the expense of smaller yellow HgI2 crystals.

Structural origin of ionic conductivity for Li7P3S11 metastable crystal by neutron and X-ray diffraction

Reverse Monte Carlo modeling was carried out for Li7P3S11 metastable crystal and (Li2S)70(P2S5)30 glass based on time-of-flight neutron and synchrotron X-ray diffraction data. Polyhedral analysis of three-dimensional structures for Li7P3S11 metastable crystal and (Li2S)70(P2S5)30 glass were gave us not only structural characteristics but also structural origins related to their high ionic conductivity.

Solubility measurement of a metastable achiral crystal of sodium chlorate in solution growth

The solubility of the metastable achiral monoclinic phase in NaClO3 crystallization from an aqueous solution, which appears prior to the nucleation of chiral crystals, was successfully measured in the range from 10°C to 23°C. Antisolvent crystallization method was used to obtain metastable crystals for the measurement. The solubility was determined to be about 1.6 times higher than that of the chiral stable cubic phase by observing growth or dissolution of the crystal in aqueous solution at the temperature and concentration of which is predetermined.

超短パルス粉末X線回折による光励起ピコ秒構造相転移計測技術の開発

We are developing an ultra-short pulse powder X-ray diffraction method using X-ray pulses of high brilliance and femtosecond pulse width from the X-ray free-electron laser apparatus in SACLA, Japan. The distinctive feature of this method is detection of anisotropic crystal structure deformation during non-thermal process. We have applied this method to some materials, including chalcogenide Ge-Sb-Te, porous coordination polymers, hydroxyhydrides, etc. In this review, we will introduce some preliminary results of observation of photo-induced anisotropic lattice expansion in a non-thermal process in a metastable face-centered cubic Ge2Sb2Te5 crystal.

The growth status of relaxor-based ferroelectric crystals and their development trends

Our progress in the growth of ternary system Pb ( In 1/2 Nb 1/2) O 3– Pb ( Mg 1/3 Nb 2/3) O 3– PbTiO 3 (PIMNT) crystals and reviews on the possible developing trends in the piezoelectric crystals are presented. Large PIMNT crystals with 3 inches in diameter have been grown by using a modified Bridgman method. Meanwhile, Mn -doped PIMNT crystals have also been obtained. PIMNT crystals exhibit Curie temperature Tc ~ 190° C , rhombohedral–tetragonal phase transition temperature T rt > 100° C and coercive field Ec ~ 5.0–7.0 kV/cm on (001) cuts. Meanwhile, higher piezoelectric constant d32 ~ -1500–2200 pC/N , d15 ~ 4000–6000 pC/N and coercive field Ec ~ 7.0–9.0 kV/cm have been achieved on (110) cuts. The development trends of relaxor-based ferroelectric crystals are suggested to grow novel crystals with high rhombohedral–tetragonal phase transition temperature T rt > 150 ~ 160° C and/or high coercive field Ec and mechanical quality factor Qm, to promote growth efficiency of PIMNT crystals and to create new growth methods fitting for the growth of metastable or instable crystals.

A weakening mechanism for intermediate-depth seismicity? Detailed petrographic and microtextural observations from blueschist facies pseudotachylytes, Cape Corse, Corsica

Gabbro- and peridotite-hosted pseudotachylytes from the Alpine Schistes Lustres Unit in Corsica, previously determined to have formed at blueschist to lawsonite-eclogite facies conditions, have been causally linked to the generation of intermediate-depth earthquakes, which occur at depths of 50–300 km. Detailed petrographic and microtextural analyses of these pseudotachylytes suggest that their initiation may be controlled by a thermally-activated shear runaway process that is controlled by rheology rather than mineralogy. This is documented by sheared out, prolate, kinked and twinned wallrock clasts that have been peeled off and entrained into the pseudotachylyte vein as sigmoid survivor clasts. The presence of metastable high temperature crystallisation products in the pseudotachylyte, such as hoppers and dendrites of olivine, enstatite and diopside (peridotite) and Al-rich omphacite and Fe-rich anorthite in metagabbro, are suggestive of a short-lived high-temperature event resulting from thermal instability. These high temperature mineral assemblages are overprinted by ones indicating a return to ambient conditions of lower temperatures, but still high pressures: glaucophane, albite and epidote in metagabbro and clinochlore; and fine-grained granoblastic olivine, enstatite and diopside in peridotite. The observations from this detailed study of natural samples suggest that intermediate-depth seismicity may be generated by a thermal runaway process.

Achiral Metastable Crystals of Sodium Chlorate Forming Prior to Chiral Crystals in Solution Growth

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P21/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 A, b = 5.26 A, c = 6.70 A, β = 109.71°) revealed that the achiral phase should be identical to Phase III (a = 8.78 A, b = 5.17 A, c = 6.83 A, β = 110°), which is a high-temperature phase from a melt growth of NaClO3. We...

Stable and metastable hard-sphere crystals in fundamental measure theory

Using fully minimized fundamental measure functionals, we investigate free energies, vacancy concentrations, and density distributions for bcc, fcc, and hcp hard-sphere crystals. Results are complemented by an approach due to Stillinger, which is based on expanding the crystal partition function in terms of the number n of free particles while the remaining particles are frozen at their ideal lattice positions. The free energies of fcc and hcp and one branch of bcc agree well with Stillinger's approach truncated at n=2. A second branch of bcc solutions features rather spread-out density distributions around lattice sites and large equilibrium vacancy concentrations and is presumably linked to the shear instability of the bcc phase. Within fundamental measure theory and the Stillinger approach (n=2), hcp is more stable than fcc by a free energy per particle of about 0.001k(B)T. In previous simulation work, the reverse situation has been found, which can be rationalized in terms of effects due to a correlated motion of at least five particles in the Stillinger picture.

Influence of NiO on phase transformations and optical properties of ZnO–Al2O3–SiO2 glass-ceramics nucleated by TiO2 and ZrO2. Part I. Influence of NiO on phase transformations of ZnO–Al2O3–SiO2 glass-ceramics nucleated by TiO2 and ZrO2

The influence of NiO addition (from 0.1 up to 3mol%) on structure and phase transformations of zinc aluminosilicate glasses nucleated by a mixture of TiO2 and ZrO2 has been studied using small angle X-ray scattering (SAXS), X-ray diffraction (XRD) analysis, Raman scattering and optical absorption spectroscopy. All parent glasses were X-ray amorphous and according to SAXS data inhomogeneous. Though SAXS intensity increased with increasing the NiO content in parent glasses, the distance between the inhomogeneous regions was independent of the NiO content implying that NiO does not play a role of additional nucleating agent. The processes of phase transformations were different for glasses doped with 0–0.1 and 1–3mol% NiO. In glasses containing 0–0.1mol% NiO, ZrTiO4 and Ni,Ti-doped gahnite crystals precipitated simultaneously starting from heat-treatment at above 730°C; traces of ZrO2 tetragonal crystals were found in glass-ceramics prepared at 1000–1200°C. In glasses doped with 1–3mol% NiO, metastable nickel titanate-zirconate crystals with fluorite-type structure and size of 4–5nm appeared during heat-treatments in the temperature range of 730–800°C, the fraction of this phase increased with the increase of the NiO content in the parent glass. Nickel titanate-zirconate crystals with fluorite structure decomposed during annealing at above 800°C. Ni,Ti-doped gahnite crystals precipitated starting from heat-treatment at 800°C; ZrO2 tetragonal crystals were formed at 900–1200°C.

Coherent GdN clusters in epitaxial GaN:Gd thin films determined by transmission electron microscopy

The detection of non-uniform magnetic element distribution and phase separation has been highly challenging in dilute magnetic semiconductor alloys. Here, we present a dedicated transmission electron microscopy (TEM) investigation of epitaxial GaN:Gd thin films and unambiguously identify the occurrence of nano-scale coherent GdN clusters. The films were grown by molecular beam epitaxy with Gd concentrations varying between 1016 and 1019 cm−3. The TEM results revealed the presence of nano-scale, coherently strained platelets lying parallel to the (0001) basal planes of the wurtzite GaN matrix. The platelet-shaped clusters consist of GdN as verified by chemically sensitive Z-contrast scanning TEM imaging. The cluster dimension as well as the displacement of the distorted lattice along the [0001] direction are quantitatively determined by high-resolution TEM based on geometric phase analysis. Dynamic strain contrast calculations taking the measured displacement field as an input parameter attained an excellent agreement with the experimental diffraction contrast results, which enables an estimate of average cluster size and distance. The GdN platelet clusters are of two monolayer thickness with a base diameter of about 2 nm for samples with low Gd concentrations (1016 cm−3) and about 4 nm for samples with high Gd concentrations (1019 cm−3). A discussion about the local stress environment establishes that the GdN platelets are incorporated in a metastable wurtzite crystal phase.

Stability and Metastability of Bromine Clathrate Polymorphs

Clathrate hydrates are crystals in which water forms a network of fully hydrogen-bonded polyhedral cages that contain small guests. Clathrate hydrates occur mostly in two cubic crystal polymorphs, sI and sII. Bromine is one of two guests that yield a hydrate with the tetragonal structure (TS), the topological dual of the Frank-Kasper σ phase. There has been a long-standing disagreement on whether bromine hydrate also forms metastable sI and sII crystals. To date there are no data on the thermodynamic range of stability (e.g., the melting temperatures) of the metastable polymorphs. Here we use molecular dynamics simulations with the coarse-grained model of water mW to (i) investigate the thermodynamic stability of the empty and guest-filled the sI, sII, TS, and HS-I hydrate polymorphs, (ii) develop a coarse-grained model of bromine compatible with mW water, and (iii) evaluate the stability of the bromine hydrate polymorphs. The mW model predicts the same relative energy of the empty clathrate polymorphs and the same phase diagram as a function of water-guest interaction than the fully atomistic TIP4P water model. There is a narrow region in water-guest parameter space for which TS is marginally more stable than sI or sII. We parametrize a coarse-grained model of bromine compatible with mW water and use it to determine the order of stability of the bromine hydrate polymorphs. The melting temperatures of the bromine hydrate polymorphs predicted by the coarse-grained model are 281 ± 1 K for TS, 279 ± 1 K for sII, and 276 ± 1 K for sI. The closeness of the melting temperatures supports the plausibility of formation of metastable sII and sI bromine hydrates.

Metastable Liquid Crystal as Time-Responsive Reaction Medium: Aging-Induced Dual Enantioselective Control

A metastable liquid crystal (LC) was found to serve as a time-responsive reaction medium, in which the enantioselectivity of a photoreaction was perfectly switched through isothermal annealing of the reaction system. When the LC salt of an enantiopure amine with a photoreactive acid was irradiated with UV/vis light, in situ photodimerization of the acid moiety proceeded smoothly to afford the (+)-isomer of the photodimer with high enantioselectivity (+86% ee). In contrast, photoirradiation of an aged sample, isothermally annealed for 20 h, gave predominantly the (-)-isomer (-94% ee). Systematic studies revealed that the reversal in selectivity originated from metastability of the LC system, which gradually transformed into a crystalline phase during annealing. This finding demonstrates the potential use of metastable aggregates as dynamic time-responsive media, reminiscent of biological systems.

Direct Observation of a Metastable Crystal Phase of LixFePO4 under Electrochemical Phase Transition

The phase transition between LiFePO4 and FePO4 during nonequilibrium battery operation was tracked in real time using time-resolved X-ray diffraction. In conjunction with increasing current density, a metastable crystal phase appears in addition to the thermodynamically stable LiFePO4 and FePO4 phases. The metastable phase gradually diminishes under open-circuit conditions following electrochemical cycling. We propose a phase transition path that passes through the metastable phase and posit the new phase's role in decreasing the nucleation energy, accounting for the excellent rate capability of LiFePO4. This study is the first to report the measurement of a metastable crystal phase during the electrochemical phase transition of LixFePO4.

Improved magnetization in sputtered dysprosium thin films

50 nm thick nanogranular polycrystalline dysprosium thin films have been prepared via ultra-high vacuum direct-current sputtering on SiO2 and Si wafers. The maximum in-plane spontaneous magnetization at T = 4 K was found to be for samples deposited on wafers heated to 350 °C with a Néel point of and a ferromagnetic (FM) transition at , measured via zero-field-cooled–field-cooled magnetization measurements, close to single-crystal values. The slightly reduced magnetization is explained in the light of a metastable face-centred cubic crystal phase which occurred at the seed interface and granularity related effects that are still noticeably influential despite an in-plane magnetic easy axis. As deposited samples showed reduced magnetization of , however their FM transition shifted to a much higher temperature of and the antiferromagnetic phase was completely suppressed probably as a result of strain.