Suppression Of Phase Transition Research Articles

Competing Mechanisms Determine Oxygen Redox in Doped Ni-Mn Based Layered Oxides for Na-Ion Batteries.

Cation doping is an effective strategy for improving the cyclability of layered oxide cathode materials through suppression of phase transitions in the high voltage region. In this study, Mg and Sc are chosen as dopants in P2-Na0.67Ni0.33Mn0.67O2, and both have found topositively impact the cycling stability, but influence the high voltage regime in different ways. Through a combination of synchrotron-based methods and theoretical calculations it is shown that it is more than just suppression of the P2 to O2 phase transition that is critical for promoting the favorable properties, and that the interplay between Ni and O activity is also a critical aspect that dictates the performance. With Mg doping, the Ni activity can be enhanced while simultaneously suppressing the O activity. This is surprising because it is in contrast to what has been reported in other Mn-based layered oxides where Mg is known to trigger oxygen redox. This contradiction is addressed by proposing a competing mechanism between Ni and Mg that impacts differences in O activity in Na0.67MgxNi0.33- xMn0.67O2 (x<0<0.33). These findings provide a new direction in understanding the effects of cation doping on the electrochemical behavior of layered oxides.

Interlayer‐Engineering and Surface‐Substituting Manganese‐Based Self‐Evolution for High‐Performance Potassium Cathode

AbstractManganese‐based layered oxides cathodes have attracted enormous interest due to their advantages in cost and energy density. The significant challenges of Mn‐based layered oxides for potassium‐ion batteries (PIBs) are complex phase transition and Mn dissolution upon K+intercalation/deintercalation. Here, a P3‐type K0.45Rb0.05Mn0.85Mg0.15O2(KRMMO) cathode material is proposed to address the above challenges. The results show that rubidium acts as a pillar to expand interlayer spacing and stabilize the structure, while magnesium partially replaces Mn to suppress the Jahn–Teller distortion of the Mn3+. The KRMMO cathode exhibits high capacity of 108.0 and 77.3 mAh g−1at 20 and 500 mA g−1, respectively, and retains 98.2% of its initial capacity after 200 cycles. Compared with P3‐K0.5MnO2, the capacity fading of P3‐KRMMO is effectively suppressed, which is mainly due to the synergistic contribution of Rb and Mg ions in the alleviation of volume change and suppression of phase transition. This work may open a new avenue for the design and optimization of layered cathode materials for PIBs and beyond.

Suppression of Phase Transitions in Perovskite Thin Films through Cryogenic Electron Beam Irradiation.

Organic-inorganic hybrid perovskites (OIHPs) with superior optoelectronic properties have emerged as revolutionary semiconductor materials for diverse applications. A fundamental understanding of the interplay between the microscopic molecular-level structure and the macroscopic optoelectronic properties is essential to boost device performance toward theoretical limits. Here, we reveal the critical role of CH3NH3+ (MA) in the regulation of the physicochemical and optoelectronic properties of a MAPbI3 film irradiated by an electron beam at 130 K. The order-to-disorder transformation of the MA cation not only leads to a notably enhanced photoluminescence emission but also results in the suppression of the orthorhombic phase down to 85 K. Taking advantage of the regulation of MA cation dynamics, we demonstrate a perovskite photodetector with 100% photocurrent enhancement and long-term stability exceeding one month. Our study provides a powerful tool for regulating the optoelectronic properties and stabilities of perovskites and highlights potential opportunities related to the organic cation in OIHPs.

A new surface phase of Al2Ti7O15 to enhance the electronic conductivity and interfacial stability of LiCoO2 cathode materials

LiCoO2 (LCO) is one of the most commonly used cathodes for lithium ion batteries applied in consumer electronics products. However, higher upper cutoff voltage (greater than4.2 V vs Li/Li+) is necessary for LCO in pursuit of higher energy density, which comes along with structural and interfacial instability of LCO. Herein, the combined modification of Al-Mg-Ti co-doping and Al2O3 coating of LCO is employed to improve the stability of LCO under 4.5 V (vs Li/Li+). As a result, the electrochemical performance, kinetic performance and the storage performance evaluated at both coin cell and pouch cell levels are promoted after the modification. Further analysis proves that the suppression of phase transition from order to disorder, and the retarded side reaction between LCO and the electrolyte are the main reasons for the enhanced performances of modified LCO. Interestingly, a new phase, Al2Ti7O15 (ATO), is discovered near the surface of the modified LCO, which is beneficial to elevating the electron conductivity and transmission property of lithium ions as demonstrated by the DFT calculation and conductivity measurement. This work provides new insights into the effect of Al-Mg-Ti co-doping on LCO materials.

Resolving the Role of Configurational Entropy in Improving Cycling Performance of Multicomponent Hexacyanoferrate Cathodes for Sodium‐Ion Batteries

AbstractMn‐based hexacyanoferrate (Mn‐HCF) cathodes for Na‐ion batteries usually suffer from poor reversibility and capacity decay resulting from unfavorable phase transitions and structural degradation during cycling. To address this issue, the high‐entropy concept is here applied to Mn‐HCF materials, significantly improving the sodium storage capabilities of this system via a solid‐solution mechanism with minor crystallographic changes upon de‐/sodiation. Complementary structural, electrochemical, and computational characterization methods are used to compare the behavior of high‐, medium‐, and low‐entropy multicomponent Mn‐HCFs resolving, to our knowledge for the first time, the link between configurational entropy/compositional disorder (entropy‐mediated suppression of phase transitions, etc.) and cycling performance/stability in this promising class of next‐generation cathode materials.

Nd-Nb co-dopant effect on suppression of phase transition, ionic conductivity and dielectrics relaxation phenomenon of La2Mo2O9 system

In the present paper, Nd, Nb co-doped La2Mo2O9 system is investigated to understand phase transition, ionic conductivity and dielectric relaxation phenomenon. X-ray diffraction study confirms order-disorder phase transition by disappearance of peak splitting of (231) in co-doped LMX system, which is associated with monoclinic phase and is observed for LMX-Pure at around 2θ = 47–48°. In co-doped system, two dielectric relaxation peaks are observed, which are associated with diffusion process between O(1)-O(2) and O(1)-O(3) oxygen ion ←→ vacancies sites, while diffusion process O(1)-O(3) is supposed to be occurred in parent system having single relaxation peak. Thus dielectric relaxation phenomenon indicates phase transition is proceeding with static-to-dynamic disorder transition. Electric modulus data are revealed to ascertain correlation of relaxation dynamics and oxy-ion conductivity in co-doped LMX system. The extracted data of activation energy of oxy-ion conductivity at intermediate temperature range (500–700 °C) of co-doped samples is found relatively lower than that of the parent sample. The study reveals that incorporation of Nd, Nb co-doped in LMX system successfully suppress the phase transition and enhanced ionic conductivity at intermediate temperature range and found suitable as electrolytes for intermediate temperature solid oxide fuel cells.

Crystallization and Phase Transition of 1‐Butene Copolymers with Distinct Cyclic Co‐Units

Comprehensive SummaryThe dimethylpyridylamidohafnium catalyst was used to synthesize 1‐butene/cyclohexene and 1‐butene/vinylcyclohexane random copolymers, which have extra six‐membered cyclic co‐units in main chain and side chain, respectively. For the obtained copolymers of different incorporations, the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry. Both of the incorporated cyclic co‐units decrease the crystallization kinetics, but the presence of cyclohexene keeps the melting temperature of copolymers constant. Interestingly, the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature, as the content of co‐units was increased. The 1‐butene/vinylcyclohexane copolymer with 1.52 mol% co‐units exhibits a rather strong memory effect with the broad Domain IIa width of 43°C and the crystallization temperature raising of 24°C. Furthermore, the transition of tetragonal phase into trigonal phase was also explored for different co‐units and incorporations. It was found that both of the cyclohexene co‐units and vinylcyclohexane co‐units effectively slow down the kinetics of phase transition. However, the vinylcyclohexane co‐units have a much higher efficiency in suppressing phase transition than the cyclohexene co‐units, where 0.53 mol% vinylcyclohexane can completely stop phase transition within 1320 h. Considering the fact that copolymers with vinylcyclohexane co‐units actually have lower glass transition temperatures, it was indicated that the suppression of phase transition is also largely influenced by the steric co‐units in the side chain for the helical and positional adjustments, not only by the segmental mobility.

Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.

Negative and Zero Thermal Expansion NiTi Superelastic Shape Memory Alloy by Microstructure Engineering

We report recent progress in tailoring the thermal expansion (TE) of nanocrystalline (NC) NiTi by microstructure hierarchical design and control without composition change. Fabrication and characterization methods are outlined and preliminary results of both experiment and mechanism-based modeling are presented to understand and get insight into the unusual TE phenomena. The important roles of the intrinsic thermal expansion anisotropy of B19′ lattice and the suppression of phase transition by the extrinsic fabricated microstructure (cold rolling and annealing, grain size, defects, textures and volume fractions of nanoscaled B2 and B19′ lattices) in the overall macroscopic TE behaviors of the superelastic NC NiTi polycrystal SMAs are emphasized.

Suppression of phase transitions at low temperature by chromium substitution in vanadium spinel Fe(V1−xCrx)2O4

Synchrotron powder diffraction, magnetization, and specific heat measurements have been used to investigate the structural and magnetic phase transitions in the spinel-type vanadate Fe(V1−xCrx)2O4 (0.0 ⩽ x ⩽ 1.0). We observed five different transitions in our polycrystalline samples. The canted-type ferrimagnetic phase transition accompanied by the lattice distortion was suppressed by Cr substitution (x = 0.2). Additionally, high-resolution synchrotron powder diffraction revealed that the low-temperature orthorhombic phase appears in FeV2O4 below 30 K and disappears by subtle Cr doping. In contrast, for x ⩾ 0.7, we observed a different magnetic transition of possibly conical-type ferrimagnetic ordering that did not induce significant lattice distortion at the transition temperature. We performed structural refinements for low-temperature phases and suggest that the crystal system of Fe(V1−xCrx)2O4 at 15K is an orthorhombic lattice for all x values. In the orthorhombic phase, a unique behaviour was observed, with the lattice constants a and b approaching each other as Cr doping increased. This behaviour can be explained by the change of orbitally ordered states of the Fe2+ ions.

Consequences of nonconformist behaviors in a continuous opinion model

.We investigate opinion formation in a kinetic exchange opinion model, where opinions are represented by numbers in the real interval [−1, 1] and agents are typified by the individual degree of conviction about the opinion that they support. Opinions evolve through pairwise interactions governed by competitive positive and negative couplings, that promote imitation and dissent, respectively. The model also contemplates another type of nonconformity such that agents can occasionally choose their opinions independently of the interactions with other agents. The steady states of the model as a function of the parameters that describe conviction, dissent and independence are analyzed, with particular emphasis on the emergence of extreme opinions. Then, we characterize the possible ordered and disordered phases and the occurrence or suppression of phase transitions that arise spontaneously due to the disorder introduced by the heterogeneity of the agents and/or their interactions.

Ionic liquids and γ-butyrolactone mixtures as electrolytes for supercapacitors operating over extended temperature ranges

Ionic liquid/solvent as high conductive electrolyte (2 mS cm−1at −50 °C) with suppression of phase transition and large electrochemical window (8 V).

Berry phases, current lattices, and suppression of phase transitions in a lattice gauge theory of quantum antiferromagnets

We consider a lattice model of two complex scalar matter fields ${z}_{a},\phantom{\rule{0.16em}{0ex}}a=1,2$, under a ${\mathbb{CP}}^{1}$ constraint $|{z}_{1}{|}^{2}+{|{z}_{2}|}^{2}=1$, minimally coupled to a compact gauge field, with an additional Berry-phase term. This model has been the origin of a large body of works addressing novel paradigms for quantum criticality, in particular ``spin-quark'' (spinon) deconfinement in $S=1/2$ quantum antiferromagnets. We map the model exactly onto a link-current model, which permits the use of classical worm algorithms to study the model in large-scale Monte Carlo simulations on lattices of size ${L}^{3}$, up to $L=512$. We show that the addition of a Berry-phase term to the lattice ${\mathbb{CP}}^{1}$ model completely suppresses the phase transition in the $\mathrm{O}(3)$ universality class of the ${\mathbb{CP}}^{1}$ model, such that the original spin system described by the compact gauge theory is always in the ordered phase. The link-current formulation of the model is useful in identifying the mechanism by which the phase transition from an ordered to a disordered state is suppressed.

Influence of field on frustrations in low-dimensional magnets

On the base of exact analytical solutions for maximum eigenvalue of Kramers–Wannier transfer matrix the phenomena of frustrations appearance and suppression of phase transition or, on the contrary, the phase transition appearance and suppression of frustrations are studied on the base of exact analytical solutions for 1D Ising model, 3-state, and 4-state standard Potts models with allowance for the interactions between nearest J and next-nearest neighbors J′, for 6-state and 8-state modified Potts models with allowance for the interaction between only nearest neighbors J. In all the models investigated we obtained exact numbers and values of frustrating fields depending, in particular, on mutual orientation of the field and spin directions.In 2D case on the example of Ising model we studied these phenomena by the numerical replica Monte Carlo method, taking into account the interactions only between nearest neighbors J and an external magnetic field of arbitrary value.We formulated the notion of thermodynamic order parameter and obtained the expressions for the entropy and heat capacity in terms of this order parameter. We also introduced the notion of frustration degree in tight connection with the order parameter. It is shown that when passing across any frustration point (either in presence or absence of magnetic field) cardinal changes of magnetic structure take place in a system.

Impact of Surface-Functionalized CdSe Nanoparticles on Phase Transitions of 8CB And CE8 Liquid Crystals

The impact of the surface–functionalised CdSe nanoparticles on various phase transitions of the two liquid crystals, 8CB and CE8, has been examined by means of high-resolution calorimetry. The addition of nanoparticles results in suppression of phase transitions and change in heat capacity anomalies. In contrast to silica aerosils CdSe nanoparticles do not form a rigid network. As a consequence, the impact of CdSe impurities on phase transitions resembles so called floppy phase regime, which exists at low concentrations of aerosils mixtures.

Suppression of Phase Transitions in a Confined Rodlike Liquid Crystal

The nematic-to-isotropic, crystal-to-nematic, and supercooled liquid-to-glass temperatures are studied in the liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) confined in self-ordered nanoporous alumina. The nematic-to-isotropic and the crystal-to-nematic transition temperatures are reduced linearly with the inverse pore diameter. The finding that the crystalline phase is completely suppressed in pores having diameters of 35 nm and below yields an estimate of the critical nucleus size. The liquid-to-glass temperature is reduced in confinement as anticipated by the model of rotational diffusion within a cavity. These results provide the pertinent phase diagram for a confined liquid crystal and are of technological relevance for the design of liquid crystal-based devices with tunable optical, thermal, and dielectric properties.

Frustrations and Phase Transitions in Low-Dimensional Magnetic Systems

The phenomena of frustrations appearance and suppression of phase transition or, on the contrary, the phase transition appearance and suppression of frustrations are studied on the base of exact solutions for 1D 3-state [1], 4-state standard [2] Potts models and the Ising model [3] with allowance for the interactions between nearest J and next-nearest neighbors J'. We also studied these phenomena in the Ising model on 2D triangular, honeycomb, and kagome lattices, using the exact analytical solutions for maximum eigenvalue of Kramers-Wannier transfer matrix [4] и [5]. In 1D case we mainly used the analytical expressions for spin-spin correlation functions and formulas for entropy and binding energy, while in 2D case, specific heat, entropy, and binding energy expressed through the maximum eigenvalue of Kramers-Wannier transfer matrix were used.

Effect of N-implantation on the structural and electrical characteristics of Ge2Sb2Te5 phase change film

In this paper, the effect of nitrogen implantation on the structure and sheet resistance of Ge2Sb2Te5 film was studied in details. It is indicated that the phase transition of Ge2Sb2Te5 film from face-centered-cubic (FCC) to hexagonal (HEX) structure was suppressed by nitrogen implantation. From the results of X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy measurements, more Te atom bonds to Sb–Sb bond and N atom bonds to Ge atom forming Ge3N4 in the nitrogen-doped Ge2Sb2Te5 film with the increase of implant dose. The sheet resistance of Ge2Sb2Te5–N film decreases with the increase of implant dose at low annealing temperature because the unit cell of crystalline Ge2Sb2Te5 film with FCC structure was distorted due to nitrogen atom occupying the tetrahedral interstitial site and the defects in film increased, which results in larger number of current carrier. On the contrary, the sheet resistance of Ge2Sb2Te5–N film increases slightly with the increase of implant dose at high annealing temperature. The two major reasons may be that the grain refinement, which results in being scattered of current carrier by grain boundary, and the suppression of phase transition from FCC to HEX structure.

Effect of O-implantation on the structure and resistance of Ge 2Sb 2Te 5 film

Ge 2Sb 2Te 5 films were deposited by rf magnetron sputtering on Si(1 0 0)/SiO 2 substrates. In order to increase the Ge 2Sb 2Te 5 sheet resistance, O + ion was implanted into Ge 2Sb 2Te 5 films. The effect of oxygen implantation on the structure of Ge 2Sb 2Te 5 film was studied in details using XRD, Raman spectra, and XPS methods. It is indicated that the structure of crystalline Ge 2Sb 2Te 5-O annealed at 250 °C is identified as a FCC structure even when oxygen implant fluence reaches 1.29 × 10 17 ions per cm 2 and the lattice parameter increases as oxygen implant fluence increasing. However, phase separation takes place when annealing temperature is 450 °C. In the case of the high fluence (higher than 6.44 × 10 16 ions per cm 2) samples, phase separation no longer takes place and phase transition from FCC to hexagonal structure is suppressed by oxygen implantation. Oxygen implantation has great effect on the resistance-annealing behaviour of Ge 2Sb 2Te 5 film, which may be origin from the structural changes including defect formation, phase separation, suppression of phase transition from FCC to hexagonal structure, and the refinement of grain size, etc. The R s of Ge 2Sb 2Te 5-O film is higher than that of Ge 2Sb 2Te 5 film when annealing temperature is higher than 340 °C, which may be caused by phase separation and current carrier scattering by crystallite boundary.

Suppression of Phase Transitions in Li-rich Lithium Cobaltite Cathodes Observed by Microparticle Cyclic Voltammetry

The electrochemical behavior of several Li-rich LiCoO 2 electrodes has been examined by microparticle cyclic voltammetry. A 10 M NaOH solution has been shown to provide a convenient aqueous phase capable to simulate the routinely employed organic Li-ion electrolytes. The voltammetric spectra show that the intercalation process undergoes to significant modifications in the case of nonstoichiometric electrodes with a nominal Li/Co atomic ratio 1.08 and beyond. In these samples the irreversible phase transitions, which are commonly believed to be responsible for the capacity fading of stoichiometric Li cobaltite materials, are clearly inhibited. The suppression effect reaches a maximum for a Li/Co ratio equal to 1.10.