Order-disorder Structural Transition Research Articles

Order-disorder structural transition and thermal expansion properties in Ce-substituted Y2Zr2O7 system

In the pursuit of advancing inert matrix fuel (IMF) applications, zirconate pyrochlores have emerged as promising candidates for the incorporation of minor actinides and plutonium. This study employs CeO2 as a nonradioactive surrogate for PuO2 and focuses on the synthesis of cerium-substituted Y2Zr2O7 samples (Y2-xCexZr2O7, 0.0 ≤ x ≤ 2.0) through a solid-state route under both reducing and oxidizing conditions to mimic plutonium incorporation. The impact of cerium content and its valence state, which in turn is influenced by synthesis conditions, on crystal structure and phase stability has been investigated through X-ray diffraction and Raman spectroscopic studies. Samples synthesized under reduced conditions undergo a defect fluorite to pyrochlore phase transition through a biphasic mixture consisting of these two phases upon increasing Ce-substitution. Conversely, the high temperature oxidizing synthesis conditions yield a defect fluorite phase field over a wide composition range (0.0 ≤ x ≤ 1.6) and a tetragonal phase at x = 2.0. Intriguingly, pyrochlore-type phases obtained under reducing conditions transform into the metastable kappa-phases upon mild oxidation at a relatively low temperature (1073 K), as confirmed by Raman spectroscopic studies. A combination of thermo-gravimetric and Raman spectroscopic investigations confirms the complete reduction of Ce4+ to Ce3+ under reducing conditions. The lattice thermal expansion behavior has also been investigated for the defect fluorite phases, synthesized under oxidizing conditions, by means of high temperature XRD spanning the temperature range 298–1273 K. Notably, the thermal expansion of compositions exhibits an increasing trend with increasing cerium content.

Slight Multielement Doping-Induced Structural Order-Disorder Transition for High-Performance Layered Na-Ion Oxide Cathodes.

To realize concurrently the high-energy density and excellent cycling stability, maximum utilization of redox couple, minimization of detrimental phase transition, and structural degradation of O3-type layered oxide cathodes are critical for developing Na-ion batteries. Ni2+/Ni4+ redox couple showing multielectron reaction and higher redox potential is favorable to increase the energy density. However, the Jahn-Teller distortion of Ni3+ generated upon (dis)charging results in a strong anisotropy in the local crystal structure that causes irreversible interlayer bending and chemo-mechanical cracks of the cathode particles, compromising the electrochemical properties eventually. In this work, we show a slight multielement doping strategy that enlarges the amount of active redox components while minimizing the inactive contents. The results show that the uniform distribution of multiple components can help increase the disorder degree of atom arrangement and alleviate the structural changes and detrimental anisotropy cracks. As a proof of concept, a multielement-doped O3-type Na0.9Ni0.25Cu0.05Mg0.05Zn0.05Fe0.05Al0.05Mn0.40Ti0.05Sn0.05O2 oxide is rationally prepared that presents better chemo-mechanical stability and delayed O3-P3 phase transition behavior. Compared to the high Ni-content Na0.9Ni0.35Fe0.2Mn0.45O2 cathode, this as-prepared multielement material delivers a reversible capacity of about 120 mAh/g in the voltage range of 2-4.0 V, superior cycling stability with 90% of capacity retention after 500 cycles, and excellent rate capability (more than 70% of initial capacity at 5.0 C). This work indicates that the multielement doping method is highly suitable for the development of advanced Na-ion layered oxide cathodes.

Elucidating Structure-Property Correlation in Perovskitoid and Antiperovskite Piperidinium Manganese Chloride.

In the world of semiconductors, organic-inorganic hybrid (OIH) halide perovskite is a new paradigm. Recently, a zealous effort has been made to design new lead-free perovskite-like OIH halides, such as perovskitoids and antiperovskites, for optoelectronic applications. In this context, we have synthesized a perovskitoid compound (Piperidinium)MnCl3 (compound 1) crystallizing in an orthorhombic structure with infinite one-dimensional (1D) chains of MnCl6 octahedra. Interestingly, this compound shows switchable dielectric property governed by an order-disorder structural transition. By controlling the stoichiometry of piperidine, we have synthesized an antiperovskite (Piperidinium)3Cl[MnCl4] (compound 2), the inverse analogue of a perovskite, consisting of zero-dimensional (0D) MnCl4 tetrahedra. This type of organic-inorganic hybrid antiperovskite halide is unique and scarce. Such a dissimilarity in lattice dimensionality and Mn2+ ion coordination ensues fascinating photophysical and magnetic properties. Compound 1 exhibits red emission with a photoluminescence quantum yield (PLQY) of ∼28%. On the other hand, the 0D antiperovskite compound 2 displays green emission with a higher PLQY of 54.5%, thanks to the confinement effect. In addition, the dimensionality of the compounds plays a vital role in the exchange interaction. As a result, compound 1 shows an antiferromagnetic ground state, whereas compound 2 is paramagnetic down to 1.8 K. This emerging structure-property relationship in OIH manganese halides will set the platform for designing new perovskites and antiperovskites.

Order-disorder structural transition of Nd2(Zr1-xCex)2O7 pyrochlores prepared by auto-combustion method

A series of pyrochlore solid solutions with general formula Nd2(Zr1-xCex)2O7 were successfully synthesized by the glycine-nitrate process (GNP) auto-combustion method and then sintered at high temperature. The order-disorder structure of the as-prepared ceramic samples was systematically characterized by X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinements of the typical XRD patterns were performed using Full-prof software. XRD and Raman results confirmed a co-existence structure composed of ordered pyrochlore and disordered defect-fluorite structure for Nd2(Zr0.75Ce0.25)2O7 and Nd2(Zr0.7Ce0.3)2O7 samples. And Nd2Ce2O7 specimen presented as defect-fluorite structure with rare earth C-type microdomains in both XRD and Raman spectroscopy. The effect of 48f oxygen on phase transition was verified by XRD and Raman spectroscopy. The refined x-parameter of 48f oxygen reflected the phase transition of Nd2(Zr1-xCex)2O7 solutions from pyrochlore to fluorite structure. High resolution transmission electron microscope (HRTEM) images and selected area electron diffraction (SAED) analysis of transmission electron microscopy (TEM) proved the representative Nd2(Zr0.7Ce0.3)2O7 sample showed biphasic structure with pyrochlore and defect-fluorite structure SAED rings. Also, the C-type microdomain SAED rings of Nd2Ce2O7 structure was found by TEM analysis.

Effects of Extrusion on Starch Molecular Degradation, Order-Disorder Structural Transition and Digestibility-A Review.

Extrusion is a thermomechanical technology that has been widely used in the production of various starch-based foods and can transform raw materials into edible products with unique nutritional characteristics. Starch digestibility is a crucial nutritional factor that can largely determine the human postprandial glycemic response, and frequent consumption of foods with rapid starch digestibility is related to the occurrence of type 2 diabetes. The extrusion process involves starch degradation and order–disorder structural transition, which could result in large variance in starch digestibility in these foods depending on the raw material properties and processing conditions. It provides opportunities to modify starch digestibility by selecting a desirable combination of raw food materials and extrusion settings. This review firstly introduces the application of extrusion techniques in starch-based food production, while, more importantly, it discusses the effects of extrusion on the alteration of starch structures and consequentially starch digestibility in various foods. This review contains important information to generate a new generation of foods with slow starch digestibility by the extrusion technique.

Order-disorder structural transition in Pr3+-doped Ba3Ga2O6 for rewritable and write-once-read-many optical data storage

The emerging challenges of the big data era, both in storage density and security, require the development of the next-generation optical data storage materials. Here, we report for the first time a photo-stimulated luminescence (PSL) material, Ba3Ga2O6: Pr3+, for rewritable optical storage and write-once-read-many data preservation. Ba3Ga2O6: Pr3+, with an isolated deep trap depth in the range 1.26–1.53eV, has been used for data encoding/decoding under the excitation of 254 nm UV light and by the simulation of an 808 nm NIR laser. Meanwhile, the phosphor allows for high-security write-once-read-many optical memory by taking advantage of the irreversible change of the photoluminescence (PL) color from blue to green (a binary blue ‘0’ and green ‘1’ code) irradiated by 365 nm UV light. The comprehensive investigations indicate that the irreversible PL switching is as a result of the order-disorder structural transition by thermal treatment. The new persistent luminescence material not only exhibits promising applications in sustainable rewritable data storage, but also paves the way for write-once-read-many optical information storage with a high level of security.

Temperature-driven order-disorder structural transition in the oxygen sub-lattice and the complex superstructure of the high-temperature polymorph of CaSrZn2Ga2O7.

Structural order-disorder plays a decisive role in the physical properties of materials, such as magnetism, second-order harmonic generation, and ionic conductivity, and it is thus widely utilized to manipulate the crystal structure and understand structure-property correlations. Herein, we report the structural polymorphism, complex crystal structure and temperature-driven irreversible order-disorder phase transition of the polar oxides (Sr1-xCax)SrZn2Ga2O7. The low-temperature (LT) structure crystallizes in Pna21 with partial Zn/Ga ordering. Upon heating, (Sr1-xCax)SrZn2Ga2O7 undergoes an irreversible phase transition from orthorhombic Pna21 to hexagonal P63. Interestingly, the high-temperature (HT) P63 structure possesses an unexpected 3/2-fold superstructure rather than a substructure of the low-temperature (LT) Pna21 structure, which is a rare structural phenomenon in solid-state chemistry. This new HT superstructure is the most complex one in this series of oxides with 21 crystallographically independent sites determined accurately by a combination of the maximum entropy method and Rietveld refinement against high-resolution neutron powder diffraction data. In terms of the mechanism, this is a temperature-driven order-to-disorder transition in the oxygen sublattice. A careful structural analysis revealed that the oxygen disordering mainly occurs in the [SrO3] layers of the HT structure and it can be understood as respective clockwise and anticlockwise rotations of distinct GaO4-tetrahedra along the c-axis. Alternating current electrochemical impedance spectroscopic analysis revealed that the oxygen disordering in the HT structure is incapable of giving rise to oxide ionic conductivity but does lead to increased electronic conduction compared to the LT structure. The optical properties of the CaSrZn2Ga2O7 and Sr2Zn2Ga2O7 representatives are also investigated in-depth via diffuse reflectance spectroscopy and theoretic calculations.

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars.

This computational study investigates the influence of light on supramolecular aggregates of three-arm azobenzene stars. Every star contains three azobenzene (azo) moieties, each able to undergo reversible photoisomerization. In solution, the azo stars build column-shaped supramolecular aggregates. Previous experimental works report severe morphological changes of these aggregates under UV–Vis light. However, the underlying molecular mechanisms are still debated. Here we aim to elucidate how light affects the structure and stability of the columnar stacks on the molecular scale. The system is investigated using fully atomistic molecular dynamics (MD) simulations. To implement the effects of light, we first developed a stochastic model of the cyclic photoisomerization of azobenzene. This model reproduces the collective photoisomerization kinetics of the azo stars in good agreement with theory and previous experiments. We then apply light of various intensities and wavelengths on an equilibrated columnar stack of azo stars in water. The simulations indicate that the aggregate does not break into separate fragments upon light irradiation. Instead, the stack develops defects in the form of molecular shifts and reorientations and, as a result, it eventually loses its columnar shape. The mechanism and driving forces behind this order–disorder structural transition are clarified based on the simulations. In the end, we provide a new interpretation of the experimentally observed morphological changes.

In-plane ordering and nature of N-doping in hard carbon synthesized at low temperature govern the sodium-ion intercalation

Graphical abstract depicting the simultaneous effect of increased in-plane ordering and N doping concentration and distribution, on the intercalation capacity of N -doped carbon microspheres (NDCMS). The highest interaction capacity is depicted by NDCMS-600 (depicting lower inplane order and high pyrrolic content), followed by NDCMS-800 (depicting longer inplane order and but lower pyrrolic N. While as lowest intercalation capacity is depicted by NDCMS-1000 which has structural features equivalent to NDCMS-600 but the lowest nitrogen concentration with negligible pyrrolic N in its structure. • The rare disorder–order-disorder structural transition and its correlation with electrochemical storage is the novel element in this work. • The simultaneous effect of hard carbon structuring and N doping (percentage and structuring) on Na storage through intercalation is observed herein. • The low-temperature carbonization proceeding with high in-plane graphitization, with high I G /I D ratios, is a unique observation presented here. • The possible influence of interplay between the N doping distribution and corresponding structural modification on the electrochemical behavior is highlighted. The inclusion of heteroatom in the hard carbon structure influences the crystal structure and electrochemical behavior to a considerable degree. Herein, we probe N- doped hard carbon series synthesized from a dairy waste at three synthesis temperatures of 600 °C, 800 °C and 1000 °C. The N -doped carbon microspheres (NDCMS) thus achieved, depict varying structural features that have been observed to hugely influence their electrochemical behavior. The rare disorder–order-disorder structural transition in the in-plane order has been observed among the NDCMS samples with NDCMS-800 depicting a high I G /I D ratio of 2.7 while NDCMS-600 and NDCMS-1000 depicted I G /I D ratio of 1.4 and 1.0 respectively. The N doping concentration varied as 4.1, 3.9, and 2.7 atom % for NDCMS-600, NDCMS-800, and NDCMS-1000, respectively. The doped N existed as pyridinic, pyrrolic, graphitic, and pyridinic oxide functionalities with NDCMS-600 possessing the 23.8 % pyrrolic N and 12.8 % graphitic N content. The N distribution changes to 8.8 % pyrrolic and 20.5 % graphitic in NDCMS-800 while the pyrrolic N content settles to 1.6 atom % and graphitic content increasing to 29.8% in NDCMS-1000. The electrochemical behavior, typically the intercalation exhibited a strong dependence on the above structural features. The NDCMS-600 with short-range order and high pyrrolic N content depicted the highest intercalation capacity of 130 mAhg −1 (total observed capacity is 171 mAhg −1 ). The NDCMS-800 which depicts lower pyrrolic content and long-range in-plane order exhibited an intercalation capacity of 102 mAhg −1 (total observed capacity is 125 mAhg −1 ). The NDCMS-1000 with reduced in-plane order and least pyrrolic content exhibits the lowest intercalation capacity of 51 mAh g −1 (total observed capacity is 75 mAh g −1 ). The intercalation kinetics is also seen to be influenced by structural variations among the NDCMS samples with R ct of ∼ 539 Ω, 787 Ω, and 1037 Ω for NDCMS-600, NDCMS-800, and NDCMS-1000 respectively.

Spectroscopic investigation of order-disorder phase transition in 4-carboxyanilinium nitrate

Co-crystal 4-carboxyanilinium nitrate (4-CAN) and its deuterated counterpart d4-CAN were studied using vibrational spectroscopy. This study is carried out to understand (i) the intra-and inter-molecular interactions in the co-crystals, 4-CAN in comparison with the parent compounds and (ii) which vibration bands of 4-CAN are affected on structural transition from monoclinic to orthorhombic phases. The Raman and infrared vibrational frequencies of 4-CAN and d4-CAN were assigned using the known frequencies of para-amino benzoic acid (PABA), partially deuterated PABA (dPABA) and HNO3. Close comparison of the spectral features of PABA and 4-CAN suggest a stronger NH…O hydrogen bond interaction and a relatively weaker hydrogen-bond interaction with the carbonyl group in 4-CAN. Temperature dependent IR study of 4-CAN across the order-disorder structural transition indicated that the vibrational bands of -NH3+ and -COOH moieties of 4-CAN are affected due to the changes taking place in hydrogen bond interaction. Present results corroborate well with the reported structural data of 4-CAN.

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

Temperature-Stimulus Responsive Ferroelastic Molecular–Ionic Crystal: (C8H20N)[BF4

Molecular–ionic crystals, which are built of organic cations and discrete anionic components with AMX4 stoichiometry, easily induce structural order–disorder transitions. These phenomena can generate interesting ferroic properties. Herein, we have synthesized and characterized a novel AMX4-type crystal, (C8H20N)[BF4] (1). Thermal analysis, (DSC, TGA) indicates one structural phase transition (PT) at 257/259 K (cooling/heating, I ↔ II). The structure of 1 has been solved at two temperatures, 120 and 298 K, with single-crystal X-ray diffraction. The high-temperature phase I (1-HT) shows a tetragonal structure with the space group I4/mmm, whereas the low-temperature phase II (1-LT) is monoclinic with the space group P21/a. The PT belongs, thus, to the improper ferroelastic species 4/mmmF2/m with a 4-fold multiplication of the unit cell. All four possible ferroelastic domains of phase II have been identified in polarized light microscopy. The monoclinic deformation has been shown to give rise to a characteristic parquet-like texture preserving integrity of 1. The molecular mechanism of PT involving changes in the cationic and anionic dynamics has been postulated based on measurements of the 1H and 19F NMR spin–lattice relaxation times, T1, and second-moment, M2, and of the dielectric responses. The ac and dc conductivity measurements have been used to determine the transport properties of the charge carriers in 1. The intrinsic features of molecular–ionic crystals, such as the dynamics of molecular motions, structural instability with a lattice-symmetry change, formation of domain patterns, etc., provide a crystal with unique ferroelastic properties. This type of crystal may be useful as an functional material.

Identification of an α-MoRF in the Intrinsically Disordered Region of the Escargot Transcription Factor.

Molecular recognition features (MoRFs) are common in intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs). MoRFs are in constant order–disorder structural transitions and adopt well-defined structures once they are bound to their targets. Here, we study Escargot (Esg), a transcription factor in Drosophila melanogaster that regulates multiple cellular functions, and consists of a disordered N-terminal domain and a group of zinc fingers at its C-terminal domain. We analyzed the N-terminal domain of Esg with disorder predictors and identified a region of 45 amino acids with high probability to form ordered structures, which we named S2. Through 54 μs of molecular dynamics (MD) simulations using CHARMM36 and implicit solvent (generalized Born/surface area (GBSA)), we characterized the conformational landscape of S2 and found an α-MoRF of ∼16 amino acids stabilized by key contacts within the helix. To test the importance of these contacts in the stability of the α-MoRF, we evaluated the effect of point mutations that would impair these interactions, running 24 μs of MD for each mutation. The mutations had mild effects on the MoRF, and in some cases, led to gain of residual structure through long-range contacts of the α-MoRF and the rest of the S2 region. As this could be an effect of the force field and solvent model we used, we benchmarked our simulation protocol by carrying out 32 μs of MD for the (AAQAA)3 peptide. The results of the benchmark indicate that the global amount of helix in shorter peptides like (AAQAA)3 is reasonably predicted. Careful analysis of the runs of S2 and its mutants suggests that the mutation to hydrophobic residues may have nucleated long-range hydrophobic and aromatic interactions that stabilize the MoRF. Finally, we have identified a set of residues that stabilize an α-MoRF in a region still without functional annotations in Esg.

Inhibited spontaneous emission using gaplike resonance in disordered photonic structures

We study the mesoscopic light transport and emission dynamics in a photonic structure made up of monodisperse scatterers as it undergoes an order-disorder structural transition. We have found a prominent tunable gaplike resonance in samples with 100% induced disorder due to the formation of clusters which consist of scatterers with short-range order. The wavelength-dependent decay rate for an emitter embedded inside the photonic structure at different levels of induced disorder is investigated. Surprisingly, the sample with 100% induced disorder exhibits comparable emission rates with 0% induced-disorder sample which indicates a similar local density of photon states (LDOS) variations in both limits of the disorder. The results are interpreted as the effect of LDOS suppression on the emission of light caused by the gaplike resonance which is in accordance with the theory.

Order-Disorder Structural Transitions in Mazes Built by Evaporating Drops.

We show that the evaporation of surfactant solutions confined in quasi-two-dimensional porous media creates micron-sized labyrinthine patterns composing the walls of a centimeter-sized maze. These walls are made of solid deposits formed during drying via a sequence of individual Haines jumps occurring at the pore scale. We rationalize this process driven by simple iterative rules with a cellular automaton that acts as a maze generator. This model well describes the formation dynamics and final structure of an experimental maze as functions of the wettability heterogeneities of a porous medium and its geometry. Also, our findings unveil the crucial role of two geometric dimensionless quantities that control the structural order of a maze.

Order-Disorder Transition in Doped Microgel Colloidal Crystals and Its Application for Optical Sensing.

Hydrogel photonic crystal-based optical sensors usually can only be used as free-standing films. Here, a doped microgel colloidal crystal film was developed as glucose sensor, which exploits structural order-disorder transition, instead of change in lattice constant, to report an analyte. Changing glucose concentration induces a change in structural order degree in the crystal and hence a change in the intensity of the stop band, and thus reports glucose concentration in the media. The response is fast and reversible. As the overall swelling degree of the gel does not change, it can be used as substrate-attached film.

Exploitation of Eu3+ red luminescence through order-disorder structural transitions in lanthanide stannate pyrochlores for warm white LED applications.

Eu3+ ions epitomize excellent structural probes for the detection of disorder induced by structural variations in stannate pyrochlores due to their relatively simple energy level structure. In this context, we have synthesized a series of Eu3+ doped Ln2.85YSnNbO10.5:0.15Eu3+ (Ln = La, Gd, Y, and Lu) red phosphors via a high temperature solid state reaction method to explore the influence of phase evolution on the luminescence properties. The substitution of Ln3+ ions in the A sites of the pyrochlore induces a structural transition from an ordered pyrochlore to a disordered fluorite structure with decreasing ionic radius. The diminishing trend of the characteristic superstructure peaks in the XRD pattern and the broadening of Raman modes with lanthanide substitution clearly substantiate the disorder induced in the cationic sublattice. These phosphors exhibit strong absorption in the near UV region and emit red luminescence under 392 nm excitation, which also correlates to their crystal structures. Their luminescence properties were enhanced with the increased ordering of cations from Lu to La. The more ordered structure of the La system favors a more uniform distribution of Eu3+ ions, preventing cluster formation, and thus improving the luminescence properties. The splitting of the 5D0-7F1 transition of the Eu3+ ions further provides a clue for the structural transition in support of the XRD and Raman analysis. The long range ordering, ligand polarizability, and covalent nature of the Eu3+ bonding influence the emission probability and improve the quantum efficiency of the La host. Eu3+ emissions resulting from 5D0-7FJ transitions are significantly improved with increases in the concentration of Eu3+ ions in the La host. The distortion of the A site symmetry and the red shift of the charge transfer band with Eu3+ doping in the La3YSnNbO10.5 system leads to an enhanced electric dipole transition. The extent of the distortion in the EuO8 polyhedra is reflected in the quantum efficiency values and J-O intensity parameters, Ω2 and Ω4, which are a measure of the degree of polarizability of the Eu-O bonds in the lattice. Our results suggest that we can manipulate the Eu3+ red luminescence in lanthanide stannate pyrochlores through order-disorder structural transitions.

Lowered pH Leads to Fusion Peptide Release and a Highly Dynamic Intermediate of Influenza Hemagglutinin.

Hemagglutinin (HA), the membrane-bound fusion protein of the influenza virus, enables the entry of virus into host cells via a structural rearrangement. There is strong evidence that the primary trigger for this rearrangement is the low pH environment of a late endosome. To understand the structural basis and the dynamic consequences of the pH trigger, we employed explicit-solvent molecular dynamics simulations to investigate the initial stages of the HA transition. Our results indicate that lowered pH destabilizes HA and speeds up the dissociation of the fusion peptides (FPs). A buried salt bridge between the N-terminus and Asp1122 of HA stem domain locks the FPs and may act as one of the pH sensors. In line with recent observations from simplified protein models, we find that, after the dissociation of FPs, a structural order-disorder transition in a loop connecting the central coiled-coil to the C-terminal domains produces a highly mobile HA. This motion suggests the existence of a long-lived asymmetric or "symmetry-broken" intermediate during the HA conformational change. This intermediate conformation is consistent with models of hemifusion, and its early formation during the conformational change has implications for the aggregation seen in HA activity.

Suppressing FePt order-disorder structural phase transition temperature by Ag doping: First principles investigation for enhancing magnetic recording density

ABSTRACTIn this work, we used density functional theory to study the structures, formation energy and order–disorder structural transition temperature (To) of L10 FePt with Ag additive. The results show that an Ag atom substituting for a Fe site is more energetically preferable than that of substituting for a Pt, thus Ag atom should replace Fe site. We found that To is significantly suppressed by Ag impurity because of the increasing in configurational entropy, whereas the magnetism tends to decrease due to the absence of some Fe atom in doping processes. The decrease in To could open the opportunity to prepare FePt with lower temperature and small grain size for the high density magnetic recording media application.

Order–disorder structural transition in a confined fluid

In this paper we analyze the amorphous/solid to disordered liquid structural phase transitions of an anomalous confined fluid in terms of their fractal dimensions. The model studied is composed by particles interaction through a two-length scales potential confined by two infinite plates. This fluid that in the bulk exhibits water-like anomalies under confinement forms layers of particles. We show that the fluid at the contact layer forms at high densities structures and transitions that can be mapped into fractal dimensions. The multi-fractal singularity spectrum is obtained in all these cases and it is used as the order parameter to quantify the structural transitions for each stage on the confined liquid. This mapping shows that the fractal dimension increases with the density and with the temperature.