Relaxation Behavior Research Articles

Slow Magnetic Relaxation in a Californium Complex.

We report the synthesis and characterization of the macrocyclic californium derivative Na[Cf(H2O)(DOTA)] (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), 1-Cf, which was studied in comparison to its dysprosium counterpart, Na[Dy(H2O)(DOTA)], 1-Dy. Divergent spectroscopic and magnetic behaviors were observed between 1-Cf and 1-Dy. Based upon spectroscopic measurements, we propose that accessible 5f → 6d transitions (potentially operating in tandem with charge-transfer transitions) are the major contributors to the observed broadband photoluminescence in 1-Cf. Dc magnetic susceptibility data for 1-Cf revealed lower magnetic moments than those previously observed for 1-Dy and expected for an f9 free ion, which calculations suggest is the result of greater ligand field effects. Notably, 1-Cf displays slow magnetic relaxation on the time scale of ac susceptibility measurements, making it the first example of a californium-based single-molecule magnet. A side-by-side comparison of the ac susceptibility data reveals magnetic relaxation properties that widely differ between 1-Cf and 1-Dy. This divergent relaxation behavior is attributed mainly to the inherent difference in spin-orbit coupling between Dy3+ and Cf3+.

Fatigue Behavior of Polymer Nanocomposites under Low-Strain Cyclic Loading: Insights from Molecular Dynamics Simulation.

Understanding the structural evolution and bond-breaking behavior under cyclic loading is crucial for designing polymer nanocomposites (PNCs) with superior fatigue resistance. Coarse-grained models of PNCs filled with spherical carbon black nanoparticles (NPs) at varying filling fractions of φ were successfully constructed using molecular dynamics simulations. Structural and dynamic simulation results reveal that higher φ leads to increased aggregation of NPs and markedly restricts the relaxation behavior of the polymer matrix. Subsequently, fatigue testing of PNCs was conducted under low-strain cyclic tensile deformation, and the real-time bond-breaking behavior was tracked. The decay behavior of the bond number autocorrelation function was found to be accurately described by the KWW equation, enabling precise determination of the characteristic lifetime τf. With increasing φ, the dominant factor influencing bond-breaking behavior gradually shifts from the polymer network, including entanglements and cross-linking networks, to the filler network. This suggests the presence of a critical filling fraction φc where τf is maximized. For low-strain failure mechanisms, temperature field observations at varying cycles reveal that localized temperature rise emerges as the predominant factor. Furthermore, the mobility of both polymers and NPs increases with cycles. Specifically, the diffusion coefficient of polymer monomers shows a clear power-law relationship with the bond-breaking rate, characterized by . Finally, the stiffness of polymer chains significantly influences the fatigue behavior, evidenced by an initial increase followed by a decrease in the τf with increasing bending energy k. This behavior is attributed to the competitive relationship between high entanglement density at low k and enhanced preorientation at high k. In summary, this study provides a general paradigm for describing failure behavior under cyclic deformation and offers insights into fatigue mechanisms at the molecular level, thereby guiding the development of improved fatigue-resistant PNCs.

Enhanced relaxor behavior and excellent anti-fatigue performance in lanthanum-modified Sr0.7Bi0.2TiO3 ceramics

Ferroelectric ceramics have attracted increasing attention for their wide applications in pulsed-power systems. Wherein relaxor ferroelectric ceramics with fast discharge speed and great stability are considered promising candidate materials. In this study, we introduced the rare-earth element La into Sr0.7Bi0.2TiO3 relaxor ferroelectric ceramics. Due to the lattice distortion triggered by La ions, the microdomains broke and transformed into high dynamic polar nano-regions (PNRs), thus improving the relaxor characteristic. We have identified this phenomenon through various characterizations, including the continuous waveform P-E (CWPE) test and the first-order reversal curve (FORC) test. With the high dynamic PNRs replacing the original domains, a better energy storage performance was achieved (Wrec = 3.22J/cm3 and η = 88.83% under 330kV/cm), and the pulse charge-discharge speed has been further improved (t0.9 = 70-81ns under 40-200kV/cm). Simultaneously, Sr0.658Bi0.188La0.04TiO3 ceramics owed remarkable anti-fatigue characteristics (0.40% attenuation after 107 cycles in the P-E test, 5.82% attenuation after 106 times in the pulse repetition frequency discharge test) due to the weak links of PNRs, revealing the great application potential of the Sr0.658Bi0.188La0.04TiO3 ceramic.

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.

Hypnotic-based intervention for people with non-communicable diseases : A scoping review

This scoping study aimed to explore the use of hypnotic-based interventions for individuals with Non-Communicable Diseases (NCDs). Four research questions were addressed: the types of hypnosis-based interventions, the types of NCDs studied, the targeted outcomes, and the evidence of effectiveness. Using Arksey and O'Malley's framework, a systematic search of databases (Cochrane Library, Google Scholar, Scopus, PubMed) was conducted from March to April 2021. Studies published in English between 2001 and 2021, employing Randomized Controlled Trials (RCTs), were included. Out of 6,382 unique records, 11 primary studies met the inclusion criteria, encompassing 589 participants across four NCD subgroups: diabetes, chronic respiratory diseases, cancer, and cardiovascular diseases. Five types of hypnotic interventions were identified: mindfulness, relaxation, self-hypnosis, hypnotherapy, and cognitive behavior therapy plus hypnosis. The outcomes assessed included pain, fatigue, anxiety, sleep quality, dyspnoea, emotion, panic, and quality of life. While the results suggest that hypnotic-based interventions hold promise as supportive therapy for NCD patients, especially in addressing psychological symptoms, the evidence remains inconclusive. Further research is needed to establish the overall effectiveness of hypnosis in this context. Nonetheless, these findings highlight the potential of hypnosis to complement medical treatments for NCDs.

In vitro bioprinted 3D model enhancing osteoblast-to-osteocyte differentiation

Abstract In vitro bone models are pivotal for understanding tissue behavior and cellular responses, particularly in unravelling certain pathologies' mechanisms and assessing the impact of new therapeutic interventions. A desirable in vitro bone model should incorporate primary human cells within a 3D environment that mimics the mechanical properties characteristics of osteoid and faithfully replicate all stages of osteogenic differentiation from osteoblasts to osteocytes. However, to date, no bio-printed model using primary osteoblasts has demonstrated the expression of osteocytic protein markers. This study aimed to develop bio-printed in vitro model that accurately captures the differentiation process of human primary osteoblasts into osteocytes. Given the considerable impact of hydrogel stiffness and relaxation behavior on osteoblast activity, we employed three distinct cross-linking solutions to fabricate hydrogels. These hydrogels were designed to exhibit either similar elastic behavior with different elastic moduli, or similar elastic moduli with varying relaxation behavior. These hydrogels, composed of gelatin (5% w/v), alginate (1%w/v) and fibrinogen (2%w/v), were designed to be compatible with micro-extrusion bioprinting and proliferative. The modulation of their biomechanical properties, including stiffness and viscoelastic behavior, was achieved by applying various concentrations of cross-linkers targeting both gelatin covalent bonding (transglutaminase) and alginate chains’ ionic cross-linking (calcium). Among the conditions tested, the hydrogel with a low elastic modulus of 8 kPa and a viscoelastic behavior over time exhibited promising outcomes regarding osteoblast-to-osteocyte differentiation. The cessation of cell proliferation coincided with a significant increase in alkaline phosphatase (ALP) activity, the development of dendrites, and the expression of the osteocyte marker PHEX. Within this hydrogel, cells actively influenced their environment, as evidenced by hydrogel contraction and the secretion of collagen I. This bio-printed model, demonstrating primary human osteoblasts expressing an osteocyte-specific protein, marks a significant achievement. We envision its substantial utility in advancing research on bone pathologies, including osteoporosis and bone tumors.

Preparation and Mechanical Properties Analysis of Rare Earth Filling Ethylene‐Allene Monomer Rubber Composite

AbstractEthylene propylene diene monomer (EPDM) rubber is used in critical sectors such as national defense, military, and aerospace. However, it has performance limitations under high temperatures, affecting its dynamic mechanical properties, creep, and stress relaxation. To overcome these limitations, rare earth cerium oxide (CeO2) was incorporated as a filler into EPDM in this study, which enhances its properties and makes it suitable for the demanding applications. It could be seen that the CeO2‐enriched EPDM has significantly improved mechanical characteristics at elevated temperatures. The Young's modulus of CeO2‐enriched EPDM increased by about 100 %, while the energy storage modulus reaches a maximum increase of around 140 % at 165 °C. The addition of CeO2 improves its damping properties, provides better creep and stress relaxation resistance, and results in greater residual strain recovery. At room temperature, the impact on the stress relaxation rate at 50 % strain is minimal for the material EPDM, and it is almost negligible for the material EPDM/CeO2.These findings demonstrate that CeO2‐enriched EPDM has enhanced performance under high‐temperature conditions. Under elevated temperature conditions, EPDM enriched with CeO2 exhibits enhanced mechanical properties, superior creep resistance, and stable stress relaxation behavior, rendering it more adept at withstanding the rigorous conditions encountered in aerospace applications.

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.