Thermodynamic Transition Research Articles

Improvement of Thermodynamic Phase Stability and High-Rate Capability of Li Layered Oxides.

The use of elemental doping in lithium cobalt oxide (LCO) cathode material at high cutoff voltage is a widely adopted technique in the field of rechargeable batteries to mitigate multiple unfavorable phase transitions. However, there is still a lack of fundamental understanding regarding the rationality of each doping element implemented in this method, specifically considering the various thermodynamic stability and phase transitions. Herein, we investigated the effect of Ti doping on an O2 phase LCO (LCTO) cathode material that exhibited enhanced rate performance. We suggest that the incorporation of Ti into an O2 phase LCO results in the mitigation of multiple-phase transitions and the improvement of phase stability, thereby yielding a high-rate-capable cathode material. Through a combination of experimental and computational calculations, we demonstrate that Ti doping improves the thermodynamic stability and kinetics of Li-ions during the cycling process.

Tunable electrocaloric effect in selective ferroelectric bilayers via electrostatics for solid-state refrigeration and microelectronics thermal management

Ferroelectric (FE) electrocaloric materials research has been blossoming worldwide for solid-state refrigeration and potential cooling systems replacing thermoelectric Peltier coolers in microelectronics. In this work, we report the outcomes from a systematic study of combined phase transition (thermodynamics) based on the phenomenological Landau theory and distributed electric field (electrostatics of thin film interfaces) in FE bilayer films. Specifically, the compositional variation of ferroelectric bilayers results in broken spatial inversion symmetry leading to asymmetric thermodynamic potentials due to a combination of normal (first- and second-order phase transition) and relaxor (dispersive dielectric constant) ferroelectric behaviors devised for efficient electrocaloric cooling effects. Extensive theoretical analyses conducted for bilayers consisting of insulating materials highlight modified phase transition temperature behavior and self-poling by effective electric field amplification arising due to bilayers’ electrostatic coupling yielding significant changes in isothermal entropy (ΔS) and adiabatic temperature (ΔT). The theoretical calculation insights supported with experimental results signify, through case studies for a combination of materials experimental parameters, that amplification of the local electric field and materials engineering maximize the number of coexisting phases at or away from the morphotropic phase boundary of constituent layers in bilayer thin film architectures, which can be applicable toward other classes of materials and multilayer systems. These are effective ways for efficient cooling, in general, and for microelectronics thermal management either directly or by developing a thermal switch with phase change materials integrated with thermoelectric coolers for residual heat dissipation, both at the system and on-chip levels.

Unusual Thermal Quenching of Photoluminescence from an Organic–Inorganic Hybrid [MnBr4]2−‐based Halide Mediated by Crystalline–Crystalline Phase Transition

AbstractThe ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)2MnBr4 (DMML=N,N‐dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr4]2− tetrahedrons that leads to non‐radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire‐new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.

Unusual Thermal Quenching of Photoluminescence from an Organic-Inorganic Hybrid [MnBr4 ]2- -based Halide Mediated by Crystalline-Crystalline Phase Transition.

The ability to generate and manipulate photoluminescence (PL) behavior has been of primary importance for applications in information security. Excavating novel optical effects to create more possibilities for information encoding has become a continuous challenge. Herein, we present an unprecedented PL temporary quenching that highly couples with thermodynamic phase transition in a hybrid crystal (DMML)2 MnBr4 (DMML=N,N-dimethylmorpholinium). Such unusual PL behavior originates from the anomalous variation of [MnBr4 ]2- tetrahedrons that leads to non-radiation recombination near the phase transition temperature of 340 K. Remarkably, the suitable detectable temperature, narrow response window, high sensitivity, and good cyclability of this PL temporary quenching will endow encryption applications with high concealment, operational flexibility, durability, and commercial popularization. Profited from these attributes, a fire-new optical encryption model is devised to demonstrate high confidential information security. This unprecedented optical effect would provide new insights and paradigms for the development of luminescent materials to enlighten future information encryption.

Control of thermodynamic liquid-liquid phase transition in a fragility-tunable glassy model.

We propose a distinguishable-particle glassy model suitable for the molecular dynamics simulation of structural glasses. This model can sensitively tune the kinetic fragility of supercooled liquids in a wide range by simply changing the distribution of particle interactions. In the model liquid, we observe the occurrence of thermodynamic liquid-liquid phase transitions above glass transition. The phase transition is facilitated by lowering fragility. Prior to the liquid-liquid phase transition, our simulations verify the existence of a constant-volume heat capacity maximum varying with fragility. We reveal the characteristics of the equilibrium potential energy landscape in liquids with different fragility. Within the Gaussian excitation model, the liquid-liquid transition as well as the response to fragility is reasonably interpreted in configuration space.

Stochastic thermodynamic engines under time-varying temperature profile

A recently developed stochastic control formalism (Stochastic Thermodynamics) has opened for the first time the possibility to quantify energy exchange and entropy production in finite-time thermodynamic transitions, based on Langevin models for mesoscopic thermodynamic systems. Within this framework we quantify power output and efficiency of overdamped stochastic thermodynamic engines that are powered by a heat bath with temperature that varies periodically with time. Our setting is in contrast to most of the existing literature that considers the Carnot paradigm, alternating contact with heat baths having different fixed temperatures, hot and cold. Specifically, we consider a periodic and bounded but otherwise arbitrary temperature profile and derive explicit bounds on the power and efficiency achievable by a suitably controlling potential that couples the thermodynamic engine to the external world – the time-varying potential represents the control input to the system. A standing assumption in our analysis is that the norm of the gradient of the potentials is bounded – in the absence of any such constraint on the control input, the physically questionable conclusion of arbitrarily large power can be drawn.

Thermodynamical and spectral phase transition for local diffeomorphisms in the circle

It is known that all uniformly expanding dynamics have no phase transition with respect to Hölder continuous potentials. In this paper we show that given a local diffeomorphism f on the circle, that is neither a uniformly expanding dynamics nor invertible, the topological pressure function is not analytical. In other words, f has a thermodynamic phase transition with respect to geometric potential. Assuming that f is transitive and that Df is Hölder continuous, we show that there exists such that the transfer operator , acting on the space of Hölder continuous functions, has the spectral gap property for all and has not the spectral gap property for all . Similar results are also obtained when the transfer operator acts on the space of bounded variations functions and smooth functions. In particular, we show that in the transitive case f has a unique thermodynamic phase transition and it occurs in t 0. In addition, if the loss of expansion of the dynamics occurs because of an indifferent fixed point or the dynamics admits an absolutely continuous invariant probability with positive Lyapunov exponent then

Boundary-induced singularity in strongly-correlated quantum systems at finite temperature

Exploring the bulk-boundary correspondences and the boundary-induced phenomena in the strongly-correlated quantum systems belongs to the most fundamental topics of condensed matter physics. In this work, we study the bulk-boundary competition in a simulative Hamiltonian, with which the thermodynamic properties of the infinite-size translationally-invariant system can be optimally mimicked. The simulative Hamiltonian is constructed by introducing local interactions on the boundaries, coined as the entanglement-bath Hamiltonian (EBH) that is analogous to the heat bath. The terms within the EBH are variationally determined by a thermal tensor network method, with coefficients varying with the temperature of the infinite-size system. By treating the temperature as an adjustable hyper-parameter of the EBH, we identify a discontinuity point of the coefficients, dubbed as the ‘boundary quench point’ (BQP), whose physical implication is to distinguish the point, below which the thermal fluctuations from the boundaries to the bulk become insignificant. Fruitful phenomena are revealed when considering the simulative Hamiltonian, with the EBH featuring its own hyper-parameter, under the canonical ensembles at different temperatures. Specifically, a discontinuity in bulk entropy at the BQP is observed. The exotic entropic distribution, the relations between the symmetries of Hamiltonian and BQP, and the impacts from the entanglement-bath dimension are also explored. Our results show that such a singularity differs from those in the conventional thermodynamic phase transition points that normally fall into the Landau–Ginzburg paradigm. Our work provides the opportunities on exploring the exotic phenomena induced by the competition between the bulk and boundaries.

Einstein-AdS Gravity Coupled to Nonlinear Electrodynamics, Magnetic Black Holes, Thermodynamics in an Extended Phase Space and Joule–Thomson Expansion

We studied Einstein’s gravity with negative cosmological constant coupled to nonlinear electrodynamics proposed earlier. The metric and mass functions and corrections to the Reissner–Nordström solution are obtained. Black hole solutions can have one or two horizons. Thermodynamics and phase transitions of magnetically charged black holes in Anti-de Sitter spacetime are investigated. The first law of black hole thermodynamics is formulated and the generalized Smarr relation is proofed. By calculating the Gibbs free energy and heat capacity we study the black hole stability. Zero-order (reentrant), first-order, and second-order phase transitions are analyzed. The Joule–Thomson expansion is considered, showing the cooling and heating phase transitions. It was shown that the principles of causality and unitarity are satisfied in the model under consideration.

Determination of thermodynamic properties and phase transition temperatures of phenylbenzoate-based calamitic liquid crystals by inverse gas chromatography method

ABSTRACT In this study, Phenylbenzoate-based calamitic liquid crystals (LCs) were synthesized and characterized, and then the thermodynamic properties and phase transition temperatures were investigated by inverse gas chromatography (IGC) at infinite dilution. The phase transition temperatures of the LCs were determined in the range of 40–170°C by the IGC method. Finally, in the thermodynamic equilibrium region (the range of 160–200°C), Flory-Huggins theory and the equation of state theory with the LC-solvent interaction parameters, the effective exchange energy parameters, the weight fraction activity coefficient, and also the partial molar heat of mixing at infinite dilution of solvent, the molar heat of vaporization of solvent, and the partial molar heat of sorption of solvent were calculated.

Thermodynamical phase transitions of AdS black hole in Horava–Lifshitz gravity

In this paper, we investigate the thermodynamical phase transitions of the spherically symmetric AdS black hole in Horava–Lifshitz (HL) gravity for the detailed balance violation parameter [Formula: see text]. First, by calculating the HP temperature [Formula: see text], the minimum temperature [Formula: see text] and the Gibbs free energy [Formula: see text] of the AdS black hole in different values of parameter [Formula: see text], we find that the HP phase transition can occur at all pressures. Comparing the HP temperature [Formula: see text] with the minimum temperature [Formula: see text], we notice that the ratio of [Formula: see text] tends to 1 when [Formula: see text]. Second, for the small–large black hole phase transition of the AdS black hole, we discover that the black hole heat capacity is divergent at the minimum temperature [Formula: see text], the small–large black hole phase transition occurs at the same time. Furthermore, the black hole entropy also exists [Formula: see text] when [Formula: see text], and [Formula: see text] when the black hole temperature has its minimum [Formula: see text], we surprisingly find that the ratio of [Formula: see text] tends to [Formula: see text] when the dimension [Formula: see text], which provides a general relation between the Hawking–Page phase transition and the small–large black hole phase transition of the AdS black hole in the large dimension. All in all, the ratios of typical temperature and entropy of two kinds of phase transitions tend to natural constant in the large dimension limit, which may imply to understand the nature of two different phase transitions.

Role of Native Defects in Fe-Doped β-Ga2O3.

Iron impurities are believed to act as deep acceptors that can compensate for the n-type conductivity in as-grown Ga2O3, but several scientific issues, such as the site occupation of the Fe heteroatom and the complexes of Fe-doped β-Ga2O3 with native defects, are still lacking. In this paper, based on first-principle density functional theory calculations with the generalized gradient approximation approach, the controversy regarding the preferential Fe incorporation on the Ga site in the β-Ga2O3 crystal has been addressed, and our result demonstrates that Fe dopant is energetically favored on the octahedrally coordinated Ga site. The structural stabilities are confirmed by the formation energy calculations, the phonon dispersion relationships, and the strain-dependent analyses. The thermodynamic transition level Fe3+/Fe2+ is located at 0.52 eV below the conduction band minimum, which is consistent with Ingebrigtsen's theoretical conclusion, but slightly smaller than some experimental values between 0.78 eV and 1.2 eV. In order to provide direct guidance for material synthesis and property design in Fe-doped β-Ga2O3, the defect formation energies, charge transitional levels, and optical properties of the defective complexes with different kinds of native defects are investigated. Our results show that VGa and Oi can be easily formed for the Fe-doped β-Ga2O3 crystals under O-rich conditions, where the +3 charge state FeGaGai and -2 charge state FeGaOi are energetically favorable when the Fermi level approaches the valence and conduction band edges, respectively. Optical absorption shows that the complexes of FeGaGai and FeGaVGa can significantly enhance the optical absorption in the visible-infrared region, while the energy-loss function in the β-Ga2O3 material is almost negligible after the extra introduction of various intrinsic defects.

Analysis of radiation defects in gallium nitride using deep level transient spectra and first principles methods

Radiation defects in gallium nitride devices were analyzed by combining experiments with simulation methods. Various forms of native defects, impurities, and these hydrogenated defect complexes in GaN were studied with first-principles calculations employing hybrid functionals which exhibit a reference data base for experimental analysis. We consider hydrogen complexes made of the combinations of single point defects (VGa, VN), di-vacancies (VGa-VGa, VN-VN, VGa-VN) and impurities (C, O, Si). Formation energies were computed for configurations with different charge states after full geometry optimizations. From the calculated formation energies, thermodynamic transition levels were evaluated, which are related to the thermal activation energies observed in experimental techniques such as deep level transient spectroscopy (DLTS). Hydrogen interstitial atoms were identified by the combination of DLTS and first-principles calculations. The transition level measured by DLTS was EC-0.5 eV, which is consistent with the calculation value. The signal of EC-0.9 eV peak in DLTS may be consisting of [VGa]-3/-2 and [VN-VN]+1/+2. According to the degradation of the electrical performance of the AlGaN/GaN high electron mobility transistors and the calculation results, the hydrogen passivation may be caused by [VGa]-3, [VGa-VGa]-2 and [VGa-VN]-1.

Hybrid DFT of electronic and vibrational properties of irondoped Β-GA2O3 crystals

This paper presents the results of calculations of energy and electron-opticalproperties of iron-doped β-Ga2O3. By analyzing the arrangement of the electronic levels of theimpurity in the band gap for different charge states, it is shown that Fe is an acceptor impurity.Evaluation of both optical and thermodynamic transition levels indicates the deep nature of theiron acceptor impurity. In addition, iron can play the role of a donor at very low Fermi energies,but the probability of forming such a state is extremely low. We find that iron modifies Ramanscattering in an ambiguous manner. Due to the low effective atomic mass of the substitutediron atom, doping leads to a pronounced enhancement of phonon modes of vibrations in thehigh-frequency range (~ 600÷800 cm-1). The results obtained are in good agreement withexperimental observations, confirming the acceptor character of the iron impurity.

Order–disorder phase transition and elastic-to-plastic vortex creep crossover in a triclinic iron pnictide superconductor (Ca_{0.85}La_{0.15})_{10}(Pt_3As_8)(Fe_2As_2)_5

Vortex matter in layered high-T_c superconductors, including iron-pnictides, undergo several thermodynamic phase transitions due to the complex interplay of pinning energy, thermal energy and elastic energy. Moreover, the presence of anisotropy makes their vortex physics even more intriguing. Here, we report a detailed vortex dynamics study, using dc magnetization measurements, in a triclinic iron-pnictide superconductor (Ca_{0.85}La_{0.15})_{10}(Pt_3As_8)(Fe_2As_2)_5, with a superconducting transition temperature, T_csim 31 K. A second magnetization peak (SMP) feature is observed for magnetic field perpendicular (Hparallelc) and parallel (Hparallelab) to the crystal plane. However, its fundamental origin is quite different in both directions. For Hparallelc, the SMP can be well explained using an elastic-to-plastic vortex creep crossover, using collective creep theory. In addition, a possible rhombic-to-square vortex lattice phase transition is also observed for fields in between the onset-field and peak-field related to the SMP. On the other hand, for Hparallelab, a clear signature of an order-disorder vortex phase transition is observed in the isothermal M(H) measurements at Tge 6 K. The disordered phase exhibits the characteristics of entangled pinned vortex-liquid. We construct a comprehensive vortex phase diagram by displaying characteristic temperatures and magnetic fields for both crystal geometries in this unique superconducting compound. Our study sheds light on the intricate vortex dynamics and pinning in an iron-pnictide superconductor with triclinic symmetry.

In-situ manifestation of the anisotropic structural thermodynamic transition of deuterated potassium dihydrogen phosphate under a strong electromagnetic field

The interaction between light and matter is a fundamental issue in nature, accompanied by the transfer of different kinds of energy and phase transitions. The discovery of the thermodynamic transition processes under strong irradiations could trigger novel phenomena and inspire the understanding of the interaction process, but it is still a challenge to observe in-situ. In this work, with the deuterated potassium dihydrogen phosphate (DKDP) crystal as a representative, the structural thermodynamic transition processes are originally investigated by introducing the in-situ neutron diffraction technique. The chemical bond fracture and breaking are found to be anisotropic, but suppressing, the destruction is not synchronous, which firstly presents the cumulative effect of energy in the structure and clarifies the relationship of the microcosmic chemical bonds and macroscopical destructions. Our results not only have important reference significance for understanding the research and development of materials under strong fields but also play an important role in understanding the physical processes of the interaction between light and matter.

Hyper Thermostability and Liquid-Crystal-Like Properties of Designed α-Helical Peptide Nanofibers.

Structural and thermodynamic transitions of artificially designed α-helical nanofibers were investigated using eight peptide variants, including four peptides with amide-modified carboxyl termini (CB peptides) and four unmodified peptides (CF peptides). Temperature-dependent circular dichroism spectroscopy and differential scanning calorimetry showed that CB peptides exhibit thermostability up to 50 °C higher than CF peptides. As a result, one of the denaturation temperatures approached nearly 130 °C, which is exceptionally high for a biomacromolecule. Thermodynamic analysis and microscopy observations also showed that CB peptides undergo a thermal transition similar to the phase transition in liquid crystals. In addition, one of the peptides showed a sharp and highly cooperative transition with a small enthalpy change at around 25 °C, which was ascribed to a giga-bundle burst of the molecular assembly. These macroscopic changes in the thermostability and crystallinity of CB peptides may be attributed to an increased amphiphilicity of the molecule in the direction of the helix axis, originating from the microscopic modification of the carboxyl-terminus.

Thermodynamic and Dynamic Transitions and Interaction Aspects in Reorientation Dynamics of Molecular Probe in Organic Compounds: A Series of 1-alkanols with TEMPO.

The spectral and dynamic properties of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in a series of 1-alkanols ranging from methanol to 1-decanol over a temperature range 100-300 K were investigated by electron spin resonance (ESR). The main characteristic ESR temperatures connected with slow to fast motion regime transition; T50G 's and TX1fast 's are situated above the corresponding glass temperatures, Tg, and for the shorter members, the T50G 's lie above or close to melting point, Tm, while the longer ones the T50G < Tm relationship indicates that the TEMPO molecules are in the local disordered regions of the crystalline media. The T50G 's and especially TX1fast 's are compared with the dynamic crossover temperatures, TXVISC = 8.72M0.66, as obtained by fitting the viscosity data in the liquid n-alkanols with the empirical power law. In particular, for NC > 6, the TX1fast 's lie rather close to the TXVISC resembling apolar n-alkanes [PCCP 2018,20,11145-11151], while for NC < 6, they are situated in the vicinity of Tm. The absence of a coincidence for lower1-alkanols indicates that the T50G is significantly influenced by the mutual interaction between the polar TEMPO and the protic polar medium due to the increased polarity and proticity destroyed by the larger-scale melting transition.

Alkali metal ion-mediated ice nucleation

Understanding the effects of ion specificities on ice nucleation is essential for atmospheric science and biology. Although valence and concentration changes of ions can regulate ice nucleation, it is unclear if alkali metal ions of different species with the same valence can regulate ice nucleation. This study investigated the behavior of ice nucleation on alkali metal ion-modified surfaces with atomic-scale roughness and (sub)nanometer thickness to decouple the effect of alkali metal ions on ice nucleation. The results showed that modulating the type of alkali metal ion could regulate ice nucleation. Additionally, it was found that different hydration shells of alkali metal ions may influence the structure of interfacial water and the thermodynamic phase transition to play a key role in regulating ice nucleation. This study shed light on a long-standing problem of the mechanism of alkali metal ions in ice nucleation and provided a strategy for effectively regulating ice nucleation .

Intercalation and Functionalization in 2D Materials

The large surface areas and interlayer gaps of 2D materials enable surface functionalization and intercalation as effective post-synthesis design knobs to tune the properties of 2D materials using ions, atoms, and organic molecules. For complete engineering control, detailed understanding of the interactions between the 2D materials and the molecules adsorbed on 2D materials surface or between the 2D materials and the intercalants is necessary.I will first discuss surface functionalization to tune the electrical properties of 2D materials. We developed an experimental approach to quantitatively measure the doping powers of organic electron donors (OEDs) to monolayer MoS2. Using novel and previously studied OEDs, we demonstrate experimentally that the measured doping power is a sensitive function of molecule’s reduction potential, size, surface coverage, and orientation to 2D materials [1, 2].I will then discuss electrochemical intercalation into 2D materials to induce novel phases that were previously undetected and to study heterointerface effects on the intercalation induced phase transition [3, 4]. We discover new structural phases in Td-WTe2 and T’-MoTe2 with lithium intercalation and these new phases are semiconducting even though the initial WTe2 and MoTe2 are semimetallic and lithium ions donate electrons to the host materials. In the lithium intercalation-induced phase transition from the 2H to 1T’ phase of MoS2, we show that the nucleation of the 1T’ phase proceeds via heterogeneous nucleation where the nature of heterointerface dictates the thermodynamics of the phase transition. For these studies, multi-modal, in-situ probes were necessary to track the changes in the structure-property relation of the layered materials as a function of intercalation.[1] Advanced Electronic Materials 7, 2000873 (2021).[2] Nano Letters 22, p.4501 (2022).[3] ACS Applied Materials & Interfaces 13, p.10603-10611 (2021).[4] Advanced Materials 34, 2200861 (2022).