Relaxation Processes In Glasses Research Articles

Dark matter searches and energy accumulation and release in materials

Efforts to identify dark matter by detecting nuclear recoils produced by dark matter particles reveal low-energy backgrounds of unknown origin in different types of detectors. In many cases, energy accumulation and delayed burst-like releases of stored energy could provide an explanation. These dynamics follow Prigogine’s ideas on systems with energy flow and the general Self-Organized Criticality scenario. We compare these models with properties of excess backgrounds in cryogenic solid-state detectors, relaxation processes in glasses and crystals, our observations of delayed luminescence in NaI(Tl), and make predictions for more phenomena present in these systems and in superconducting photon detectors and qubits. Experiments to create accurate phenomenological models are needed.

Crystal nucleation in a glass during relaxation well below Tg.

Until quite recently, in almost all papers on crystal nucleation in glass-forming substances, it was assumed that nucleation proceeds in a completely relaxed supercooled liquid and, hence, at constant values of the critical parameters determining the nucleation rate for any given set of temperature, pressure, and composition. Here, we analyze the validity of this hypothesis for a model system by studying nucleation in a lithium silicate glass treated for very long times (up to 250 days) in deeply supercooled states, reaching 60K below the laboratory glass transition temperature, Tg. At all temperatures in the considered range, T < Tg, we observed an enormous difference between the experimental number of nucleated crystals, N(t), and its theoretically expected value computed by assuming the metastable state of the relaxing glass has been reached. Analyzing the origin of this discrepancy, we confirmed that the key parameters determining the nucleation rates change with time as a result of the glass relaxation process. Finally, we demonstrate that, for temperatures below 683K, this particular glass almost fully crystallizes prior to reaching the ultimate steady-state nucleation regime (e.g., at 663K, it would take 176 years for the glass to reach 99% crystallization, while 2600 years would be needed for complete relaxation). This comprehensive study proves that structural relaxation strongly affects crystal nucleation in deeply supercooled states at temperatures well below Tg; hence, this phenomenon has to be accounted for in any crystal nucleation model.

Resolving the mixed-alkali effect on the viscoelastic behavior of supercooled liquids

Relaxation processes in mixed-alkali metaphosphate glasses and supercooled liquids are studied using a combination of calorimetric, electrical impedance spectroscopic and rheological measurements to investigate the atomistic nature of the mixed-alkali effect (MAE) on the glass transition temperature Tg and viscous flow. While Tg and fragility index of single-alkali liquids are controlled by the segmental motion of phosphate chains, the mixed-alkali liquids exhibit the presence of a second relaxation process, which is slower than chain motion and is characterized by a lower activation energy. This process is assigned to the scission and renewal of P-O bonds that relieve the accumulated stress in the network resulting from its matrix-mediated coupling with pairwise hopping of dissimilar alkalis. The viscous flow and glass transition in mixed-alkali phosphate liquids appear to be controlled by this P-O bond scission-renewal process, which is shown to be consistent with a lowering of their fragility index and a concomitant decrease in the stretching exponent of structural relaxation, compared to their single-alkali counterparts.

Governing mechanism of ion transport in lithium-iron-phosphate glasses

We show a fundamental relationship between network structural attributes and ionic transport of lithium iron phosphate glasses xLi2O–2Fe2O3–3 P2O5 (xLFPO; x = 0.375, 0.75, 1.5, 3.0) used for a cathode in lithium-ion batteries. The glass samples have been synthesized using a solid-state reaction method. We have investigated the electrical characteristics of the glass by combinational measurements of electrical impedance in the frequency 100 Hz – 30 MHz and temperature from ambient to 240 °C, differential thermal analysis, X-ray diffraction pattern, and Raman spectroscopy. The ionic hopping and relaxation processes in xLFPO glasses are analyzed by using Cole-Cole, power law, and modulus representations. We reveal that the exponential increase in dc conductivity with increasing Li2O in xLFPO glasses is caused by the combination of an increase in non-bridging oxygen sites and a change in the bonding forces of iron valence surrounding the iron phosphate clusters inside the network. The power law conductivity, which is driven by the fractional Rayleigh equation, exhibits that the rate of increase in dc ionic conductivity is the same as the rate of increasing numbers of the ionic charge carriers. Raman spectra show that the increase of depolymerization of the iron phosphate network with the addition of Li2O content is due to the conversion of Q2 to Q1 and Q0 species.

Modeling the relaxation and crystallization kinetics of glass without fictive temperature: Toy landscape approach

AbstractRelaxation and crystallization are key kinetic processes that must be understood to build a comprehensive understanding of the supercooled liquid and glassy states. Traditional approaches have been unable to capture the underlying physics accurately due to assumptions about phenomenological order parameters such as fictive temperature. In this work, we show that glass relaxation can be accurately modeled through a simplified “toy” enthalpy landscape approach, bypassing the use of fictive temperature. Moreover, the same simplified enthalpy landscape provides insights into the thermodynamics and kinetics of crystallization. The toy landscape approach recovers key predictions from the traditional fictive temperature description, but it is based on a more accurate physical framework, giving fundamental knowledge of the glass relaxation and crystallization processes.

Influence of molecular geometry on the formation, architecture and dynamics of H-bonded supramolecular associates in 1-phenyl alcohols

Combination of calorimetric, dielectric, infrared, diffraction studies and quantum DFT computations was used to analyze the impact of the molecular architecture of a set of four 1-phenyl alcohols (1-phenylethanol, 1-phenyl-1-propanol, 1-phenyl-1-butanol and 2-methyl-1-phenyl-1-propanol) on their glass transition temperature, molecular dynamics, relaxation processes, hydrogen-bonding pattern and intermolecular association. We showed that all these alcohols form H-bonded supramolecular nanoassociates even at room temperature, despite containing a steric hindrance in the form of the phenyl ring in the most disfavored position. However, the concentration and the size of the H-bonded structures as well as the mutual arrangement of molecules in these clusters are tremendously affected by the molecular architecture. In linear-shaped 1-phenyl alcohols, i.e., 1-phenylethanol, 1-phenyl-1-propanol, 1-phenyl-1-butanol, the intermolecular O-H···O bonds organize themselves into chain-like patterns. Moreover, these alcohols are characterized by similar strength of intermolecular H bonds at each temperature and similar glass transition temperature. In turn, the globular molecular shape of 2-methyl-1-phenyl-1-propanol leads to a weakening of H bonds in this system, an increase in the glass transition temperature and the formation of supramolecular clusters in which O-H···O connections imply ring-like organization of molecules. Finally, these studies clearly show that unlike the glass transition temperature, the molecular dynamics of the 1-phenyl alcohols in the liquid state is not only affected by the molecular architecture and hydrogen bond strength but also by the morphology of the associates composed of H-linked molecules.

The Structure and Magnetic Properties of Rapidly Quenched Fe72Ni8Nb4Si2B14 Alloy.

The complex structural and magnetic studies of the annealed rapidly quenched Cu-free Fe72Ni8Nb4Si2B14 alloy (metallic ribbons form) are reported here. Based on the calorimetric results, the conventional heat treatment process (with heating rate 10 °C/min and subsequent isothermal annealing for 20 min) for wound toroidal cores has been optimized to obtain the least lossy magnetic properties (for the minimum value of coercivity and magnetic core losses at 50 Hz). For optimal conditions, the complex permeability in the 104–108 Hz frequency range together with core power losses obtained from magnetic induction dependence up to the frequency of 400 kHz was successfully measured. The average and local crystal structure was investigated by the use of the X-ray diffraction method and the transmission electron microscopy observations and proved its fully glassy state. Additionally, for the three temperature values, i.e., 310, 340 and 370 °C, the glass relaxation process study in the function of annealing time was carried out to obtain a deeper insight into the soft magnetic properties: magnetic permeability and cut-off frequency. For this type of Cu-free soft magnetic materials, the control of glass relaxation process (time and temperature) is extremely important to obtain proper magnetic properties.

Revealing the ultra-low-temperature relaxation peak in a model metallic glass

By systematically investigating the relaxation behavior of a model metallic glass based on the extensive molecular dynamics (MD) simulations combined with the dynamic mechanical spectroscopy method, a pronounced ultra-low temperature peak on the loss modulus spectrum was discovered for the first time in MD simulations. It was found that the relaxation peak occurs at a much lower temperature than the typical temperature for the conventional β relation peak as reported in the literature. According to the atomic displacement analysis, we unravel that the reversible atomic motions, rather than the thermal vibrations or local structural rearrangements, mainly contribute to this relaxation peak. We further identify the atomic level mechanism of this fast relaxation process by characterizing the local geometrical anisotropy. Furthermore, by tracing the dynamic behaviors of these “reversible” atoms, we demonstrate the intrinsic hierarchy of the relaxation modes, which are triggered by atomic vibrations and gradually developed to include the reversible and irreversible atomic movements. Our findings provide an important piece of the puzzle about the holistic picture of the rich relaxation processes in metallic glasses.

Exploring the role of lignin structure in molecular dynamics of lignin/bio-derived thermoplastic elastomer polyurethane blends

The relaxation behavior of two lignins (Alcell organosolv, OSL, and hydroxypropyl modified Kraft, ML) and bio-based thermoplastic polyurethane (TPU) blends have been studied by Differential scanning calorimetry (DSC), Dynamic-mechanical analysis (DMA) and Dielectric relaxation spectroscopy (DRS). The effect of blending on the glass and local relaxation processes as a function of composition, frequency, and temperature has been assessed. The dielectric spectra were resolved into dipolar relaxations as well as conductive processes for differing blend compositions. Characteristic relaxation times, activation energies and dielectric relaxation strengths of lignin/xTPU blends were also investigated. It was found that blending suppresses the α-relaxation process of the blends compared to virgin TPU. On the other hand, while the position of the β-relaxation was not influenced by blending, a reduction of the activation energies, Ea, of this process was observed in the lignin/xTPU blends. Finally, changes are observed in the conductivity behavior of both blends, with conductivity processes more favorable for the OSL/xTPU blends.

Intrinsic heterogeneity of shear banding: Hints from diffusion and relaxation measurements of Co micro-alloyed PdNiP-based glass

The influence of Co micro-alloying (1 at. %) on the shear band diffusion and the relaxation processes in a model PdNiP bulk metallic glass is investigated. The shear bands are induced by one-pass cold-rolling. In addition to a fast shear band diffusion branch (Dsb≃10−16m2/s at 473 K), with the diffusivity being similar to that observed for the cold-rolled standard Pd40Ni40P20 composition, an ultrafast diffusion branch (Dsb≃10−14m2/s at the same temperature) is found to exist in the micro-alloyed glass. Combined with previously reported observations of faster relaxation of both the Boson peak height and the fictive temperature, the results indicate that Co micro-alloying affects the excess free volume distribution and thus changes the potential energy landscape of the glass, introducing a higher number of local atomic arrangements prone to the formation of shear transformation zones under plastic deformation.

Revealing the Low-Temperature Fast Relaxation Peak in a Model Metallic Glass

By systematically investigating the relaxation behavior of a model metallic glass based on the extensive molecular dynamics (MD) simulations combined with the dynamic mechanical spectroscopy method, a pronounced ultra-low temperature peak on the loss modulus spectrum was discovered for the first time in MD simulations. It was found that the relation peak occurs at a much lower temperature than the typical temperature for the conventional β relation peak as reported in the literature. According to the atomic displacement analysis, we unravel that the atomic motions, rather than the thermal vibrations or local structural rearrangements, mainly contribute to this relaxation peak. We further identify the atomic level mechanism of this fast relaxation process by characterizing the local geometrical anisotropy. Furthermore, by tracing the dynamic behaviors of these reversible atoms, we demonstrate the intrinsic hierarchy of the local relaxation modes, which are triggered by atomic vibrations and gradually developed to the and irreversible atomic movements. Our findings shed light on a general picture of the relaxation processes in metallic glasses.

Physical properties and conductivity relaxation processes in sodium sulfo-borophosphate glasses

Many physical properties of a sodium-borophosphate glass system (BPSx) having the starting composition (30H3BO3 + xNa2SO4 + (60 − 2x) NaH2PO4 + 10ZnO) were detremined. It was found that the glass density ρ, the transition temperature Tg, and the optical gap energy decrease whereas the molar volume and Urbach ▵E energy increases with the substitution of Na2O by Na2SO4.The analysis of the evolution of the complex dielectric permittivity ε* and the complex electric modulus M* with temperature and composition of the glass indicates that the dielectric loss is dominated by ionic conduction, and the relaxation processes are non-Debye type. The evolution of the Kohlrausch–Williams–Watts (KWW) exponent β, estimated from the imaginary part of the electric modulus indicates that the investigated glass behaves as an intermediate elastic system as compared to flexible and stressed rigid phase. The obtained values of the decoupling index are of the same order of magnitude as observed for fast-ion conducting glasses.From the analysis of the experimental data, we may suggest that the glass sample BPS4 is the more thermally stable and has the highest ionic conductivity since it has the highest dielectric constant favorable for the dissociation of sodium salt.

A Microporous Co(II)‐Based 3‐D Metal Organic Framework Built from Magnetic Infinite Rod‐Shaped Secondary Building Units

The synthesis and characterization of {[Co5(INA)3(HCOO)7(DMF)(H2O)]·2DMF·4H2O}∞ (INA– = the anion of isonicotinic acid) denoted as Co5‐INA·2DMF·4H2O is reported. The compound was isolated from the reaction of Co(NO3)2·6H2O with HINA in the presence of HCOOH in N,N‐dimethylformamide (DMF) at 100 °C. It exhibits a rigid 3‐D porous structure based on Co5 repeating units which are linked through carboxylate ligands (from HCOO– and INA–) to form an infinite rod‐shaped secondary building unit (SBU). The rods are connected through isonicotinate ligands to produce a unique (3,3,4,4,4‐coordinated) 5‐nodal 3D network with point symbol (4.5.6.72.9)(4.5.62.7.8)(4.5.7)2(5.62.73). Gas sorption studies revealed that Co5‐INA displays a microporous structure with BET area 264.5 m2 g–1 and CO2 uptake of 1.96/1.29 mmol·g–1 at 273/298 K (1 bar), respectively. Magnetism studies revealed that Co5‐INA displays spin canting behavior with a spin glass relaxation process at ca. 5.0 K.

Predicting Complex Relaxation Processes in Metallic Glass.

Relaxation processes significantly influence the properties of glass materials. However, understanding their specific origins is difficult; even more challenging is to forecast them theoretically. In this study, using microseconds molecular dynamics simulations together with an accurate many-body interaction potential, we predict that an Al_{90}Sm_{10} metallic glass would have complex relaxation behaviors: In addition to the main (α) relaxation, the glass (i)shows a pronounced secondary (β) relaxation at cryogenic temperatures and (ii)exhibits an anomalous relaxation process (α_{2}) accompanying α relaxation. Both of the predictions are verified by experiments. Computational simulations reveal the microscopic origins of relaxation processes: while the pronounced β relaxation is attributed to the abundance of stringlike cooperative atomic rearrangements, the anomalous α_{2} process is found to correlate with the decoupling of the faster motions of Al with slower Sm atoms. The combination of simulations and experiments represents a first glimpse of what may become a predictive routine and integral step for glass physics.

Effect of iron oxide on the electrical conductivity of soda-lime silicate glasses by dielectric spectroscopy

A survey of relaxation processes in glasses exhibiting ionic and electronic–ionic conductivity mechanisms is presented. Electrical conductivity and dielectric properties are investigated using complex impedance spectroscopy in a frequency range from 0.1 to 106 Hz and a temperature range from 253 to 423 K. The results reveal that ionic conduction depends on the alkali concentration and ion mobility while electrical conduction is only slightly influenced by alkali ions and a mixed electronic–ionic conduction can occur. The Jonscher’s expression of ac electric conductivity is modified by adding a new term taking into account the displacement current density associated with the dielectric relaxation. The change in the activation energy depends upon the chemical composition indicating a changeover of the predominant conduction mechanism from ionic to polaronic. Quantum mechanical tunneling (QMT) model was suggested to describe the conduction mechanism of alkali-silicate glass G1 where frequency exponent s 1, whose conduction mechanism may be considered in terms of the optical phonon assisted hopping of small polarons between overlapping states. The electrical modulus exhibited relaxation character.

Method for calculating stress evolution in glass-metal composite taking into account structural and mechanical relaxation processes

Technological modes of annealing layered glass-metal composite material are investigated. A cylindrical glass-metal composite vessel with an internal glass cylinder is used as a model sample in the experimental studies of highly compressed fragile rocks mass. A mathematical model of the evolution of technological and residual stresses during its annealing is considered. The difficulty in modeling is due to the glass transition process and the elastic-plastic behavior of the metal. Structural and mechanical relaxation processes in glass are calculated using the Tula-Naariswami-Moynihan-Mazurin method, which is based on the concept of structural temperature, and the Boltzman-Volterra superposition principle. The dependence of viscosity and coefficient of linear temperature expansion on the structural temperature is taken into account. Elastic state in the stress space is limited by the surface of the Mises limit state for metal shell. In this paper, a finite-difference scheme for calculating structural changes and process stresses over the entire temperature treatment interval is proposed. To assess the accuracy of the developed calculation algorithm, we used an analytical solution of the problem with the Maxwell core in the absence of temperature-time analogy in glass and elastic deformation of the metal layer. Calculations of technological stresses in glass metal composite based on borosilicate glass and low carbon steel for various temperature regimes of annealing were carried out. The proposed mathematical model and calculation method can be used for evaluating residual stresses in the technology of applying glass coatings on metal pipes.

The impact of micro-alloying on relaxation dynamics in Pd40Ni40P20 bulk metallic glass

The impact of Co micro-alloying on low temperature specific heat capacity and the relaxation processes in a model Pd40Ni40P20 bulk metallic glass in both as-cast and cold-rolled states was investigated. In addition to an excess (Boson) peak at low temperatures of about 12 to 14 K, a magnetic heat capacity anomaly in the Co alloyed glass below 10 K was observed. The measured Boson peak heights and the fictive temperatures both advocate a much faster β relaxation in the micro-alloyed glass. Yet, the micro-alloying does not measurably affect the enthalpy associated with α-relaxation. The impact of shear bands on the thermodynamic properties of the micro-alloyed glass is discussed.

Main α relaxation and slow β relaxation processes in a La30Ce30Al15Co25 metallic glass

Dynamic relaxation processes are fundamental to understand the mechanical and physical properties of metallic glasses. In the current work, mechanical relaxations in a La30Ce30Al15Co25 bulk metallic glass were probed by dynamic mechanical analysis. In contrast to many metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced slow β relaxation peak. Physical aging below the glass transition temperature Tg leads to an increase of the apparent activation energy and a decrease of the slow β relaxation magnitude. The correlation between the slow β relaxation and the main α relaxation is discussed.

Influence of Concentration Fluctuations on Relaxation Processes in Spin Glasses

Using the unique combination of atomically resolved atom probe tomography (APT) and volume averaged neutron (resonance) spin echo (NRSE and NSE) experiments, the influence of nano-scaled clusters on the spin relaxation in spin glasses was studied. For this purpose, the phase transition from the paramagnetic phase to the spin glass phase in an Fe-Cr spin glass with a composition of Fe 17 . 8 Cr 82 . 2 was studied in detail by means of NRSE. The microstructure was characterised by APT measurements, which show local concentration fluctuations of Fe and Cr on a length scale of 2 to 5 nm, which lead (i) to the coexistence of ferro- and anti-ferromagnetic clusters and (ii) a change of the magnetic properties of the whole sample, even in the spin glass phase, where spins are supposed to be randomly frozen. We show that a generalized spin glass relaxation function, which was successfully used to describe the phase transition in diluted spin glasses, can also be used for fitting the spin dynamics in spin glasses with significant concentration fluctuations.

Influence of vibration on basalt fiber crystallization at high temperature

The influence of low-frequency vibrational treatment on the crystallization of basalt wool fibers was studied. In this work, three series of samples were investigated. The first sample set was only one-sided heated at temperatures from 300 °C to 900 °C for 24 h. The second sample set was after only vibrational treatment with a frequency of 50 Hz and oscillations amplitude of 1 mm for 6–48 h. The third sample set was after simultaneous treatment of one-sided heating and vibration at temperatures from 300 °C to 600 °C with a frequency of 50 Hz and oscillations amplitude of 1 mm for 24 h. It is shown that at temperatures close to the glass transition temperature, vibration can influence on the relaxation processes in glasses and accelerate them. Mechanism of glass structure transformation in the basalt fiber does not change, but it starts at a slightly lower temperature. That is a consequence of an additional low-energy vibrational treatment. The vibrational treatment intensifies the crystallization process in basalt fibers and decreases the service temperature of the material by at least 40–50 °C.