Relaxation Behavior Research Articles

What will be the Euclidean dimension of an Ising ferromagnetic cubic shell?

The equilibrium and nonequilibrium properties of an Ising ferromagnetic cubic shell have been extensively studied by Monte Carlo simulation using Metropolis single spin flip algorithm. Although, geometrically the Euclidean dimension of the cubical shell is three, interestingly, the Ising ferromagnetic cubic shell undergoes ferromagnetic phase transition at a temperature which is very close to that for two-dimensional Ising ferromagnet. Surprisingly, the Ising ferromagnetic cubic shell shows a strange (neither exponential nor stretched exponential) kind of relaxation behaviour, instead of exponential relaxation as usually observed in the two dimensional Ising ferromagnet. The metastable lifetime of a ferromagnetic Ising cubical shell is studied as a function of the applied magnetic field. Here also, the cubic shell behaves more likely a two-dimensional object as found from statistical analysis and comparison with Becker-Döring prediction of classical nucleation theory.

Lanthanide‐Based Molecular Magnetic Semiconductors

AbstractMagnetic semiconductors, with integrated properties of ferromagnets and semiconductors, are significant for developing next‐generation spintronic devices. Herein two atomically precise clusters of dysprosium(III) tellurides, formulated respectively as [Na2(15‐crown‐5)3(py)2][(η5‐Cp*Dy)5(Te)6](py)4 (Dy5Te6, Cp*=pentamethylcyclopentadienyl; py=pyridine) and [K(2,2,2‐cryptand)]2[(η5‐Cp*Dy)6(Te3)(Te2)2(Te)3] (Dy6Te10), are reported. Crystallographic studies revealed the presence of multifarious tellurido ligands within the polyhedral cluster cores. Spectroscopic and magnetic studies showed that both clusters are single‐molecule magnets exhibiting slow magnetic relaxation behaviors at low temperatures and semiconductors with low optical band gaps comparable to benchmark semiconductors. These clusters represent probably the first lanthanide‐based molecular magnetic semiconductors.

Chiral Homodinuclear Dysprosium Macrocyclic Complexes with Single‐Molecule Magnetic Behaviours

AbstractA pair of enantiomerically chiral dysprosium homodinuclear complexes: [(acac)4Dy2(R,R,R,R‐L)] (R‐Dy) and [(acac)4Dy2(S,S,S,S‐L)] (S‐Dy) (Hacac=acetylacetone) have been synthesized based on macrocyclic chiral ligands (R,R,R,R‐H2L or S,S,S,S‐H2L), derived from the [2+2] template condensation of 4‐tert‐butyl‐2,6‐diformylphenol, dysprosium acetylacetonate and (1R,2R)‐/(1S,2S)‐1,2‐cyclohexanediamine, respectively. Circular dichroism spectra confirms their enantiomeric chirality. Single‐crystal structures show two crystallographic independent dysprosium(III) ions have square antiprismatic coordination with different D4d local symmetry. Furthermore, the selected R‐Dy complex owns the slow magnetic relaxation behaviour with the ferromagnetic Dy3+⋅⋅⋅Dy3+ coupling.

The impact of relative humidity on the nanoindentation relaxation in calcium silicate hydrates

Despite extensive research efforts, understanding the time-dependent behavior of concrete remains an enigma due to the complex nature of cement microstructure. In this study, the statistical nanoindentation was employed to investigate the influence of relative humidity (RH) on the relaxation behavior of calcium silicate hydrates (C-S-H) in a cement paste. Our experiments, performed at RH levels of 33 % and 86 %, revealed significant enhancements in both the indentation modulus and hardness of the C-S-H as RH increased. Remarkably, the internal water exerted a significant influence on the asymptotic relaxation behavior, displaying a clear power-law fashion. Further analysis identified the presence of short- and long-term viscoelastic behaviors within the C-S-H, distinguished by a transition observed within the initial seconds. These findings advance the understanding of nanoscale mechanisms driving concrete creep under different humidity conditions.

Enhanced functionalities of isovalently substituted 0.67(Bi1-xLaxFe0.97Ga0.03O3)-0.33(BaTiO3) relaxor piezoceramics synthesized via air quenching

The isovalently substituted lead-free binary solid solution, 0.67(Bi1-xLaxFe0.97Ga0.03O3)-0.33(BaTiO3) (BF-BT) (x ≤ 0.07), has been synthesized by solid state ceramic method via air quenching sintering. FTIR and XRD along with Rietveld structure refinement confirmed a pure perovskite phase with a pseudocubic structure (space group Pm3‾m) for developed compositions. SEM revealed a dense microstructure with fine grain size (<1.5 μm) and minimal porosity. XPS analysis reveals predominantly Bi+3 and Fe+3 states, along with oxygen vacancies (VO··). Ferroelectric studies demonstrated a maximum remanent polarization (Pr) of 12.3 μC/cm2 and coercive field EC of 30.95 kV/cm for La3+ concentration of x = 0.03. Overall decrement in Pr can be attributed to dipolar defect-induced random fields reducing the activation barrier for domain nucleation. Leakage current measurement reveals improved resistivity (∼108 Ω cm) up to an applied field of 30 kV/cm. Dielectric measurements unveiled two frequency-dependent anomalies in temperature dependence above room temperature, indicative of diffuse phase transitions. The Vogel-Fulcher model depicted an increasing freezing temperature (from 465 K for x = 0.01–551 K for x = 0.07) and decreasing activation energy (from ∼0.61 eV to 0.07 eV) with increasing La3+ concentration. The estimated diffuseness parameter around ∼2 suggested relaxor behavior. Doping with La resulted in increased dielectric permittivity at 10 kHz (from 4100 to 24066), showcasing the efficacy of site engineering in augmenting the functional properties of BF-BT for high-temperature dielectric and transducer applications.

Improving the Energy Storage Performance in Bi0.5Na0.5TiO3-Based Ceramics by Combining Relaxor and Antiferroelectric Properties.

Ceramic capacitors have received great attention for use in pulse power systems owing to their ultra-fast charge-discharge rate, good temperature stability, and excellent fatigue resistance. However, the low energy storage density and low breakdown strength (BDS) of ceramic capacitors limit the practical applications of energy storage technologies. In this work, we present a series of relaxor ferroelectric ceramics (1-x) [0.94 Bi0.5Na0.5TiO3 -0.06BaTiO3]- x Sr0.7Bi0.2TiO3 (1-x BNT-BT- x SBT; x = 0, 0.20, 0.225, 0.25, 0.275 and 0.30) with improved energy storage performances by combining relaxor and antiferroelectric properties. XRD, Raman spectra, and SEM characterizations of BNT-BT-SBT ceramics revealed a rhombohedral-tetragonal phase, highly dynamic polar nanoregions, and a reduction in grain size with a homogeneous and dense microstructure, respectively. A high dielectric constant of 1654 at 1 kHz and low remnant polarization of 1.39 µC/cm2 were obtained with the addition of SBT for x = 0.275; these are beneficial for improving energy storage performance. The diffuse phase transition of these ceramics displays relaxor behavior, which is improved with SBT and confirmed by modified the Curie-Weiss law. The combining relaxor and antiferroelectric properties with fine grain size by the incorporation of SBT enables an enhanced maximum polarization of a minimized P-E loop, leading to an improved BDS. As a result, a high recoverable energy density Wrec of 1.02 J/cm3 and a high energy efficiency η of 75.98% at 89 kV/cm were achieved for an optimum composition of 0.725 [0.94BNT-0.06BT]-0.275 SBT. These results demonstrate that BNT-based relaxor ferroelectric ceramics are good candidates for next-generation ceramic capacitors and offer a potential strategy for exploiting novel high-performance ceramic materials.

Nanoscopically Confined 1,4-Polybutadiene Melts: Exploring Confinement by Alumina Nanorod and Nanopore Systems.

We present molecular dynamics simulations of a chemically realistic model of 1,4-polybutadiene (PBD) in contact with curved alumina surfaces. We contrast the behavior of PBD infiltrated into alumina pores with a curvature radius of about three times the radius of gyration of the chains to its behavior next to a melt dispersed alumina rod of equal absolute curvature. These confinement types represent situations occurring in polymer melts loaded with nanoparticles due to nanoparticle aggregation. While there are observable differences in structure and dynamics due to the different types of geometric confinement, the main effects stem from the strong attraction of PBD to the alumina surfaces. This strong attraction leads to a deformation of the chains in contact to the surfaces. We focus on temperatures well above the bulk glass transition temperature, but even at these high temperatures, the layers next to the alumina surfaces show glass-like relaxation behavior. We analyze the signature of this glassy behavior for neutron scattering or nuclear magnetic resonances experiments.

Synergistic regulation of Nd2O3 doping and components accommodation to attain enhanced electrical performance in BiScO3-PbTiO3 high temperature ceramics

Nd2O3-modified BiScO3-PbTiO3 (Nd: BS-PT) ceramics were synthesized with the aim of augmenting the piezoelectric response. A comprehensive investigation was conducted to explore the impact of Nd and PT content on the structure, microstructure, and electrical properties of Nd: BS-PT ceramics. The introduction of Nd ions resulted in notable enhancements in the piezoelectric and dielectric properties of BS-PT ceramics. In the case of 0.02Nd: BS-0.64PT, the piezoelectric coefficient (d33) reached an impressive 550 pC/N. Furthermore, the room-temperature dielectric constants exhibited a continuous increase with rising Nd content. The relaxation behavior demonstrated a progressive augmentation corresponding to the increased Nd content. Conversely, both saturation polarization and remnant polarization exhibited a gradual decline with increasing Nd content. These variations are attributed to the refined microstructure and enhanced relaxation behavior induced by Nd doping. This innovative Nd: BS-PT ceramic demonstrates that judicious incorporation of Nd can markedly enhance the piezoelectric properties of BS-PT ceramics. Such a modification significantly augments the performance of BS-PT ceramics across various applications, notably in sensors and actuators.

Analysis of the Sr2GdTi2Nb3O15 ceramic: Investigation into its structural properties and complex impedance spectroscopy

In this study, we successfully synthesized tetragonal tungsten bronze with the nominal formula Sr2GdTi2Nb3O15 and systematically examined of its structure, dielectric, and electrical properties. The material was synthesized through the solid-state reaction technique at a temperature of 1350 °C. The formation of the tetragonal tungsten bronze in the P4/mbm space group was verified via Rietveld refinement using X-ray diffraction data. The electrical characteristics of the ceramic were examined using non-destructive complex impedance spectroscopy (CIS) across a range of frequencies (10–106 Hz) at various temperatures. The real component of impedance (Z') displayed a decrease with rising frequency, suggesting a negative temperature coefficient of resistance (NTCR) for this sample. The Cole-Cole plot of the compound exhibits two semicircles, with the compound's resistance gradually decreasing as the temperature increased. Moreover, the activation energy (Ea) was found to be approximately 0.9 eV, which confirms that oxygen vacancies are responsible for the observed relaxation behavior. Complex modulus analysis confirmed the presence of non-Debye relaxations. These results contribute to a thorough comprehension of the structural and electrical characteristics of Sr2GdTi2Nb3O15, opening avenues for potential applications in diverse electronic devices.

Abnormal Relaxation Behavior of Excited Electrons in the Flat Band of Kagome Compound Nb3Cl8.

Carrier dynamics is crucial in semiconductors, and it determines their conductivity, response time, and overall functionality. In flat bands (FBs), carriers with high effective masses are predicted to host unconventional transport properties. The FBs usually overlap with other trivial energy bands, however, making it difficult to accurately distinguish their carrier dynamics. In this paper, we have investigated the flat-band carrier dynamics of excited electrons in Nb3Cl8, which hosts ideal nonoverlapping FBs near the Fermi level. The optical transition between Hubbard bands is abnormally weakened, exhibiting weak interband absorption and its related slow photoresponse with a time constant of ∼120 s, which are associated with flat-band Mottness-induced large electron effective mass and parity-forbidden transitions. Besides, the localized states created by chlorine vacancies also act as trapping centers for carriers with a time constant of ∼600 s, which are similar to those of the compact localized states of the FB, making the relaxation behavior even more extraordinary. The presence and impacts of atomic defects are confirmed experimentally and theoretically. This work has revealed the abnormal flat-band carrier dynamics of Nb3Cl8, which is essential for understanding the optical, electrical, and thermal transport properties of flat-band materials.

Automated Robustness Verification of Concurrent Data Structure Libraries against Relaxed Memory Models

Clients reason about the behavior of concurrent data structure libraries such as sets, queues, or stacks using specifications that capture well-understood correctness conditions, such as linearizability. The implementation of these libraries, however, focused as they are on performance, may additionally exploit relaxed memory behavior allowed by the language or underlying hardware that weaken the strong ordering and visibility constraints on shared-memory accesses that would otherwise be imposed by a sequentially consistent (SC) memory model. As an alternative to developing new specification and verification mechanisms for reasoning about libraries under relaxed memory model, we instead consider the orthogonal problem of library robustness , a property that holds when all possible behaviors of a library implementation under relaxed memory model are also possible under SC. In this paper, we develop a new automated technique for verifying robustness of library implementations in the context of a C11-style memory model. This task is challenging because a most-general client may invoke an unbounded number of concurrently executing library operations that can manipulate an unbounded number of shared locations. We establish a novel inductive technique for verifying library robustness that leverages prior work on the robustness problem for the C11 memory model based on the search for a non-robustness witness under SC executions. We crucially rely on the fact that this search is carried out over SC executions, and use high-level SC specifications (including linearizability) of the library to verify the absence of a non-robustness witness. Our technique is compositional - we show how we can safely preserve robustness of multiple interacting library implementations and clients using additional SC fences to guarantee robustness of entire executions. Experimental results on a number of complex realistic library implementations demonstrate the feasibility of our approach.

Investigation on Polyether Sulfone Toughening Epoxy Vitrimer: Curing and Dynamic Properties.

Diglycidyl ether of bisphenol A crosslinking with glutaric anhydride is used to form the conventional "covalent adaptive network", polyether sulfone (PES) by coiling and aggregating on the adaptive network is used to significantly increase the uncured resin viscosity for improving the processability of epoxy resin, but inevitably affecting the curing reaction and dynamic transesterification reaction. This study investigates the crucial roles of PES in curing dynamics and stress relaxation behavior. The results indicate that although PES does not directly participate in the crosslinking reaction of polyester-based epoxy vitrimers. Moreover, the isothermal curing studies reveal that the addition of PES can greatly bring forward the reaction rate peak from conversion α = 0.6 to α = 0.2, meaning that the curing mechanism transfers from chemical control to diffusion control. Dynamic property analysis shows that the addition of PES significantly accelerates stress relaxation, especially at lower temperatures, leading to low viscous flow activation energy Eτ and relatively insensitive stress relaxation behavior to temperature. Introducing PES into vitrimer resin greatly improves crosslinking density (2.31×10⁴molm- 3), enhancing glass transition temperature (82.68°C), tensile strength (68.66MPa), and fracture toughness (6.25%). Additionally, the modified vitrimer resin exhibits satisfying shape memory performance and reprocessing capability.

Exploring the Magnetism of C5/C2B3 Heteroleptic Organolanthanide Sandwiches

Comprehensive SummaryTwo families of cyclopentadienyl (Cp)/carboranyl heteroleptic sandwiched organolanthanide complexes, namely [Ln{η5:σ‐Me2C(C5H4)(C2B10H10)}2][Li(DME)3] (1Ln, Ln = Tb, Dy, Ho, Er) and [2‐THF‐2'‐(μ2‐Cl)Li(THF)3‐2,2'‐Ln(nido‐1,7‐C2B9H11)Cp*] (2Dy), were synthesized. Family of 1Ln has been proposed based on the mixing‐ligands idea by linking Cp and nido‐dicarborllide. However, the carborane cage of [Me2C(C5H4)(C2B10H10)]2− deprotons and forms a mono‐C− anion rather than deboron to form dicarborllide dianion. Hence, the family of 1Ln features a dysprosocenium skeleton with extra two coordination of C− anions of carborllides. Such coordination geometry is more like a tetrahedron if abstracting the centroids of two coordinated Cp rings. In this cubic‐type geometry, no significant magnetic axiality is presented; only 1Dy and 1Tb show field‐induced slow magnetic relaxation behavior below 10 K. Inspired by 1Ln, the free pentamethylcyclopentadienyl (Cp*−) and nido‐dicarborllide ligands are used to sandwich central Dy3+ ion, achieving heteroleptic complex 2Dy. The bending angle by linking the centroid of Cp*−, Dy3+ and C2B32− in 2Dy is increased to 132.8(1)°. As such, the effective energy barrier for magnetic reversal (Ueff) and magnetic blocking temperature TB (ZFC) are both increased (Ueff = 616(10) K; TB = 6 K). The effort of further enhancing Ueff and TB in such heteroleptic organolanthanide sandwiches should rely on keeping increasing the ligand axiality.

A cooperative relaxation model with two physical parameters for investigating the temperature and cure dependence of relaxation mechanisms in resins

Modeling the relaxation properties of resin matrix during cure plays an important role in predicting process-induced residual stresses and final distortions of resin-based composites. This paper develops a physical characterization model, which explains the temperature and cure-degree dependence of relaxation behaviors in terms of the size of cooperatively rearranging region, and special emphasis is placed on investigating the general physical mechanism of cure degree affecting the relaxation properties. In this model, the relaxation time is governed by a modified Adam-Gibbs equation, which is extended here to include the cure dependence. In addition, the relaxation modulus is modeled in a chemo-rheologically simple manner (CSM) based on the free volume theory. Material characterization is carried out using experimental data of two typical resins. It is shown that two cure-dependent model parameters, i.e., the smallest size of the cooperatively rearranging region and the glass transition temperature, are sufficient in accounting for the effect of cure on the relaxation modulus, and could provide a physical explanation of the influence of cure on relaxation behaviors. Furthermore, the proposed model is numerically realized by incorporating ABAQUS with UMAT subroutine, and its validity in predicting the residual stresses and final distortion of composites is also numerically verified by comparing with the results available in literature.

Enhanced energy storage performance of tungsten bronze structured BaNb2O6-modified (Bi0.5Na0.5)TiO3 ceramics

The rapid development of the electronic devices and increasing attention to environmental problems have put forward a huge demand for high-performance lead-free dielectric energy storage ceramics. In this work, tungsten bronze structured BaNb2O6 (BN) modified perovskite structured (Bi0.5Na0.5)TiO3 (BNT) ceramics, BNT-xBN (0 <x< 0.15), were prepared to optimize the energy storage performance of BNT. The results show that the lattice distortion and dielectric relaxation behavior of BNT ceramic can be induced by BN addition. Meanwhile, the introduction of tungsten bronze structured BN results in the grain refinement and the increasing of resistivity, thereby significantly enhancing the electrical breakdown strength (Eb). Accordingly, the BNT-0.1BN ceramic displays good energy storage performance with high recoverable energy density (Wrec ∼ 3.41 J/cm3) at an great Eb of 358 kV/cm, accompanied by the wide temperature stability at 30–150 °C (Wrec varies within ±12.8 %, efficiency (η) varies within ±6.7 %). The enhanced energy storage performance demonstrates that introducing tungsten bronze structure is a feasible method to prepare high-performance perovskite energy storage ceramics.

Advanced sensor performance: Investigating complexities of electrical resistance relaxation behavior in piezoresistive materials

Advanced sensor performance: Investigating complexities of electrical resistance relaxation behavior in piezoresistive materials

Microscopic analysis of relaxation behavior in nonlinear optical conductivity of graphene

We produce a general formalism to study the interband dynamical optical conductivity in the nonlinear regime of graphene in the presence of a quantum bath comprising phonons and electrons. When a quantum solid of graphene is subjected to an intense electric field in the optical frequency range, the observation of a nonlinear response is facilitated by formulating a quantum master equation of the density operator associated with the Hamiltonian encapsulated in a spin-boson model of dissipative quantum statistical mechanics. Our results reveal the nonlinear steady-state regime’s population inversion and decoherence. The present method enables us to investigate further the nonlinear interband optical conductivity of pristine and gapped graphene characterized by a single dimensionless parameter at finite temperatures. Different bath spectra’ effects on phonons and electrons are examined in detail. The temperature dependence of conductivity reveals that changing temperature can enable us to make a transition from the linear to the nonlinear regime for fixed optical field parameters. Interestingly, a fascinating switching-like behavior is observed for the low-temperature optical conductivity of the gapped graphene while we vary the energy gap as well as the frequency of the externally applied field. Although our general formulation can address a variety of nonequilibrium responses of the two-band system, it also facilitates a connection with the phenomenological modeling of nonlinear optical conductivity.

Effect of trace grain boundary segregation element bismuth on stress relaxation behavior of copper

The stress relaxation resistance of copper-based materials determines the reliability of contact and stable transmission of connector plugs. This study investigates the effect of trace bismuth (110 wt ppm) on the stress relaxation resistance of pure copper at temperatures of 25 °C, 100 °C, and 200 °C. The relationship between microstructure and stress relaxation resistance was analyzed using SEM, EBSD, and HAADF-STEM. The results demonstrate that trace bismuth significantly enhances the stress relaxation resistance of pure copper, especially at higher temperatures of 100 °C and 200 °C, where the stress relaxation rates of Cu-0.011Bi samples after 48 h decreased by 21.36 % and 18.06 %, respectively, compared to Cu samples. Trace bismuth elements exist in copper mainly in the form of double atomic layers segregated at grain boundaries, which pin the grain boundaries, inhibit grain growth, and hinder dislocation slip. At room temperature (25 °C), bismuth mainly improves stress relaxation resistance by refining grains. At higher temperatures of 100 °C and 200 °C, the significant enhancement in stress relaxation resistance is primarily related to bismuth's inhibition of the reduction in dislocation density and recrystallization during the stress relaxation process.

Investigating the multiferroic properties within triphasic systems to comprehend the mechanisms of water splitting

In the present study, a triphasic-based system was prepared using constituents such as Lanthanum Calcium Manganite (LCM), Cobalt Ferrite (CF), and Barium Titanate (BT) in different proportions. The composition (1-x)LCM: x(0.7CF-0.3BT), where x = 0, 0.1, 0.2, 0.3, and 1, was employed to produce the triphasic system-based materials using a solid-state reaction technique. X-ray diffraction results confirmed the development of the triphasic phase in the composites through the JCPDS card number of the major peaks. The average crystallite size calculated from XRD data was found to vary with increasing 0.7CF-0.3BT concentration in LCM. FTIR spectroscopy indicates alterations in the main peaks with an increase in content of 0.7CF-0.3BT, suggesting the formation of triphasic composites. The upward trend in dielectric permittivity suggests the successful occurrence of Maxwell-Wagner polarization, indicating relaxor behavior at lower frequency values. Impedance spectroscopy reveals dielectric relaxation and the contribution of charge carriers in triphasic composites, along with the impact of grain and grain boundaries. Magnetization analysis at room temperature approves an increase in saturation magnetization in composites i.e., 0.7LCM-0.3(0.7CF-0.3BT) triphasic material exhibiting a maximum saturation magnetization of 13.04 emu/g. Magnetoelectric behaviour is observed in triphasic materials at different AC magnetic fields. The 0.9LCM-0.1(0.7CF-0.3BT) triphasic hydroelectric cell achieved a peak current of 1.29 mA and showed enhanced stability over time. Its I-V characteristics revealed a short-circuit current of 3.5 mA, an open-circuit voltage of 0.85 V, and an off-load power output of 2.97 mW. The triphasic system demonstrates improved structural, electrical, and hydroelectric cell (HEC) performance offering promising prospects for use in magnetoelectric and hydroelectric devices.

Effect of alumina or zirconia particles on the performance of lead-free BCZT piezoceramics

The barium titanate derivative Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) offers high dielectric and piezoelectric performance but has poor mechanical properties. Ceramic composite materials combining BCZT with tougher Al2O3 or ZrO2 could be the solution to the inherent brittleness of electroceramics. This work focuses on BCZT with 1–5 vol.% addition of reinforcing phase dispersed in the microstructure. While hardness was improved in all composites, especially in ZrO2-reinforced BCZT, toughness was positively affected only by Al2O3. The chemical reactivity of BCZT during sintering resulted in the formation of new barium aluminate phases at the grain boundaries and possibly also within the grains, which affected the electrical properties of the composites. The addition of zirconia resulted in the formation of BaZrO3 or Ba(Zr,Ti)O3, which is a natural part of the BCZT solid solution and shifts the phase composition towards relaxor behaviour. ZrO2-reinforced composites exhibited higher permittivity but lower ferroelectric properties, accompanied by a substantial Curie temperature decrease.