The low temperature specific heat of Sm-AI-Co ternary metallic glasses is investigated and a clear anomaly associated with the Boson peak is identified. While this anomaly depends slightly on the chemical composition,...The low temperature specific heat of Sm-AI-Co ternary metallic glasses is investigated and a clear anomaly associated with the Boson peak is identified. While this anomaly depends slightly on the chemical composition, it has no dependence on external magnetic field. To figure out the mechanism of the Boson peak, we interpret the data within various model frameworks. Unlike earlier work, our study shows that this Boson peak is mainly ascribed to an additional T2 term of the specific heat, which may originate from the quasi-two-dimensional and short-range ordered structure units possibly existing in the metallic glasses.展开更多
We investigate the effects of high pressure and physical aging on the boson peak and thermal expansion of a typical metallic glass. Specifically, the thermal expansion coefficient and boson peak intensity monotonicall...We investigate the effects of high pressure and physical aging on the boson peak and thermal expansion of a typical metallic glass. Specifically, the thermal expansion coefficient and boson peak intensity monotonically decrease during physical aging.With the increase of high pressure, the boson peak intensity and the thermal expansion coefficient coincidently experience an incipient decrease and then a subsequent increase. The boson peak intensity shows an approximately linear relationship with the thermal expansion coefficient. The thermal expansion can be affected by structural relaxation or rejuvenation, which can reflect the flow units variation and atomic packing of a metallic glass. Our results indicate a direct link between structural relaxation or rejuvenation and fast boson peak dynamics, providing insights into the boson peak behavior and structural heterogeneity of metallic glasses.展开更多
We study the evolution of the Boson peak for water confined in cement paste obtained by means of Inelastic Neutron Scattering from room temperature to the deep supercooled regime.We analyze the data in terms of a univ...We study the evolution of the Boson peak for water confined in cement paste obtained by means of Inelastic Neutron Scattering from room temperature to the deep supercooled regime.We analyze the data in terms of a universal-like model,developed for glass forming liquids in the frame of the energy landscape.In such a way it is possible to discriminate between the fragile and strong glass forming character of supercooled liquids and the dynamical crossover,fragile to strong,between them.Hence,we confirm the link between the Boson peak and the water polymorphism.In particular,the main result is represented by a crossover from a local energetic minima configuration to that characteristic of saddle points on going towards the deep supercooled regime up to the dynamical arrest.展开更多
Boson peak of glasses,a THz vibrational excess compared to Debye squared-frequency law,remains mysterious in condensed-matter physics and material science.It appears in many different kinds of glassy matters and is al...Boson peak of glasses,a THz vibrational excess compared to Debye squared-frequency law,remains mysterious in condensed-matter physics and material science.It appears in many different kinds of glassy matters and is also argued to exist in damped crystals.A consensus is that boson peak originates from the coupling of the(quasi)-localized non-phonon modes and the plane-wave-like phonon modes,but the coupling behavior is still not fully understood.In this paper,by modulating the content of localized modes and the frequencies of phonon modes,the coupling is clearly reflected in the localization and anharmonicity of low-frequency vibrational modes.The coupling enhances with increasing cooling rate and sample size.For finite sample size,phonon modes do not fully intrude into the low frequency to form a dense spectrum and they are not sufficiently coupled to the localized modes,thus there is no Debye level and boson peak is ill-defined.This suggestion remains valid in the presence of thermal motions induced by temperature,even though the anharmonicity comes into play.Our results point to the coupling of quasi-localized and phonon modes and its relation to the boson peak.展开更多
Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace ...Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.展开更多
By introducing four fundamental types of disorders into a two-dimensional triangular lattice separately, we determine the role of each type of disorder in the vibration of the resulting mass-spring networks. We are co...By introducing four fundamental types of disorders into a two-dimensional triangular lattice separately, we determine the role of each type of disorder in the vibration of the resulting mass-spring networks. We are concerned mainly with the origin of the boson peak and the connection between the boson peak and the transverse Ioffe-Regel limit. For all types of disorders, we observe the emergence of the boson peak and Ioffe-Regel limits. With increasing disorder, the boson peak frequency ωBP, transverse Ioffe-Regel frequency ω^TIR, and longitudinal Ioffe-Regel frequency wLn all decrease. We find that there are two ways for the boson peak to form： developing from and coexisting with （but remaining independent of） the transverse van Hove singularity without and with local coordination number fluctuation. In the presence of a single type of disorder, ωTR 〉 wBp, and ωTIR≈BP only when the disorder is sufficiently strong and causes spatial fluctuation of the local coordination number. Moreover, if there is no positional disorder, ωTIR ≈ωLIR. Therefore, the argument that the boson peak is equivalent to the transverse Ioffe-Regel limit is not general. Our results suggest that both local coordination number and positional disorder are necessary for the argument to hold, which is actually the case for most disordered solids such as marginally jammed solids and structural glasses. We further combine two types of disorders to cause disorder in both the local coordination number and lattice site position. The density of vibrational states of the resulting networks resembles that of marginally jammed solids well. However, the relation between the boson peak and the transverse Ioffe-Regel limit is still indefinite and condition-dependent. Therefore, the interplay between different types of disorders is complicated, and more in-depth studies are required to sort it out.展开更多
We report the pronounced low-temperature specific-heat Cpanomalies in the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)bulk metallic glass(BMG).The extrapolated electron’s temperature coefficientγ0Kis up to 681.8 mJ/(molGd·...We report the pronounced low-temperature specific-heat Cpanomalies in the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)bulk metallic glass(BMG).The extrapolated electron’s temperature coefficientγ0Kis up to 681.8 mJ/(molGd·K^(2))at 0 K,which is a heavy-fermion-like behavior.The low temperature specific heat indicates an enhancement of the conduction-electron effective mass m*below 7.5 K,suggesting that the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)BMG is not free-electron-like solid.The excess specific heat in the Mg-based BMG is interpreted with tunneling states and spin glass state(magnetism)which are determined by subtracting electrons’and phonons’contribution to the specific heat below 12 K.The Boson peak(BP)temperature is located at 27 K,which is much higher than the reported values of other BMGs.And,a BP height of 0.047 mJ/(mol·K^(4))is obtained due to reduced free volume during copper mold casting with a slow cooling rate.The electrical resistivity was also investigated between 2 and 300 K,which has a negative temperature coefficient of resistivity(TCR)below 35 K(Kondo temperature,TK)and a positive value of 3.9×10^(-4)/K above 35 K.There is a minimum at about 35 K for the electrical resistivity,which can be explained by the Kondo effect.For the resistivity above 35 K,it can be explained by the FaberZiman model due to the T-dependence change of structure factor.展开更多
The glass transition involves more than one dynamic relaxation mechanisms in supercooled liquids,such as α relaxation,slow β relaxation and fast β relaxation and so on.For the traditional theoretical system,α rela...The glass transition involves more than one dynamic relaxation mechanisms in supercooled liquids,such as α relaxation,slow β relaxation and fast β relaxation and so on.For the traditional theoretical system,α relaxation is believed mainly responsible for the nature of the glass transition as the beginning of the phenomenon.This idea,however,has been open to a big challenge since recent studies have indicated that slow β relaxation closely relates to α relaxation.Slow β relaxation determines the characteristics of α relaxation and is the precursor and the more microscopic base of glass transition behavior.In order to illuminate the significance of slow β relaxation in the fields of the glass transition and the structure of supercooled liquids,the accomplished progress is summarized from different aspects such as on the correlation between α relaxation and slow β relaxation,on the manner of α-slow β relaxation merging,on the energy landscape,on the excess wing and on the thermodynamically phenomenological models.The tendency of investigation in slow β relaxation is also evaluated.展开更多
Rejuvenation of glassy structures in general is characterized by the exothermic enthalpy prior to the glass transition.In the present work,we find that this situation is not applicable to a heavily-aged Zr-based metal...Rejuvenation of glassy structures in general is characterized by the exothermic enthalpy prior to the glass transition.In the present work,we find that this situation is not applicable to a heavily-aged Zr-based metallic glass that rejuvenates by anelastic deformation before yield.Instead,its rejuvenation can be precisely captured by the low-temperature boson heat capacity peak as well as the effective enthalpy change with the glass-to-liquid transition.These results demonstrate that a structurally stable glass could rejuvenate by decreasing mechanical stability of its basin of potential energy landscape,but without changing the basin's energy level.The underlying mechanism points toward the redistribution of the atomic free volume with a constant system-averaged value.We further find that the rejuvenation limit of this glass is its steady-flow state with self-similar inherent structures at both short-and long-time scales.Our findings refresh the understanding of glass rejuvenation and suggest that the boson peak is a better probe for the structural rejuvenation of glasses.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50601013, 10674061 and 50832002)the National Basic Research Program of China (Grant No. 2006CB921802)
文摘The low temperature specific heat of Sm-AI-Co ternary metallic glasses is investigated and a clear anomaly associated with the Boson peak is identified. While this anomaly depends slightly on the chemical composition, it has no dependence on external magnetic field. To figure out the mechanism of the Boson peak, we interpret the data within various model frameworks. Unlike earlier work, our study shows that this Boson peak is mainly ascribed to an additional T2 term of the specific heat, which may originate from the quasi-two-dimensional and short-range ordered structure units possibly existing in the metallic glasses.
基金supported by the National Natural Science Foundation of China(Grant Nos.51801083,11790291,51461165101,51801124,and51671211)the Natural Science Foundation of Jiangsu Province(Grant No.BK20181044)。
文摘We investigate the effects of high pressure and physical aging on the boson peak and thermal expansion of a typical metallic glass. Specifically, the thermal expansion coefficient and boson peak intensity monotonically decrease during physical aging.With the increase of high pressure, the boson peak intensity and the thermal expansion coefficient coincidently experience an incipient decrease and then a subsequent increase. The boson peak intensity shows an approximately linear relationship with the thermal expansion coefficient. The thermal expansion can be affected by structural relaxation or rejuvenation, which can reflect the flow units variation and atomic packing of a metallic glass. Our results indicate a direct link between structural relaxation or rejuvenation and fast boson peak dynamics, providing insights into the boson peak behavior and structural heterogeneity of metallic glasses.
基金Emiliano Fratini and Piero Baglioni acknowledge partial financial support from Consorzio per lo Sviluppo dei Sistemi a Grande Interfase(CSGI)
文摘We study the evolution of the Boson peak for water confined in cement paste obtained by means of Inelastic Neutron Scattering from room temperature to the deep supercooled regime.We analyze the data in terms of a universal-like model,developed for glass forming liquids in the frame of the energy landscape.In such a way it is possible to discriminate between the fragile and strong glass forming character of supercooled liquids and the dynamical crossover,fragile to strong,between them.Hence,we confirm the link between the Boson peak and the water polymorphism.In particular,the main result is represented by a crossover from a local energetic minima configuration to that characteristic of saddle points on going towards the deep supercooled regime up to the dynamical arrest.
基金Project supported by the National Outstanding Youth Science Fund Project(Grant No.12125206)the Fund from the Basic Science Center for“Multiscale Problems in Nonlinear Mechanics”(Grant No.11988102)the General Project of the National Natural Science Foundation of China(Grant No.11972345)。
文摘Boson peak of glasses,a THz vibrational excess compared to Debye squared-frequency law,remains mysterious in condensed-matter physics and material science.It appears in many different kinds of glassy matters and is also argued to exist in damped crystals.A consensus is that boson peak originates from the coupling of the(quasi)-localized non-phonon modes and the plane-wave-like phonon modes,but the coupling behavior is still not fully understood.In this paper,by modulating the content of localized modes and the frequencies of phonon modes,the coupling is clearly reflected in the localization and anharmonicity of low-frequency vibrational modes.The coupling enhances with increasing cooling rate and sample size.For finite sample size,phonon modes do not fully intrude into the low frequency to form a dense spectrum and they are not sufficiently coupled to the localized modes,thus there is no Debye level and boson peak is ill-defined.This suggestion remains valid in the presence of thermal motions induced by temperature,even though the anharmonicity comes into play.Our results point to the coupling of quasi-localized and phonon modes and its relation to the boson peak.
基金supported by the National Outstanding Youth Science Fund Project (Grant No. 12125206)Basic Science Center for “Multiscale Problems in Nonlinear Mechanics”(Grant No. 11988102)+1 种基金General Project of National Natural Science Foundation of China (Grant No. 11972345)CAS Project for Young Scientists in Basic Research (Grant No. YSBR-096)。
文摘Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.
文摘By introducing four fundamental types of disorders into a two-dimensional triangular lattice separately, we determine the role of each type of disorder in the vibration of the resulting mass-spring networks. We are concerned mainly with the origin of the boson peak and the connection between the boson peak and the transverse Ioffe-Regel limit. For all types of disorders, we observe the emergence of the boson peak and Ioffe-Regel limits. With increasing disorder, the boson peak frequency ωBP, transverse Ioffe-Regel frequency ω^TIR, and longitudinal Ioffe-Regel frequency wLn all decrease. We find that there are two ways for the boson peak to form： developing from and coexisting with （but remaining independent of） the transverse van Hove singularity without and with local coordination number fluctuation. In the presence of a single type of disorder, ωTR 〉 wBp, and ωTIR≈BP only when the disorder is sufficiently strong and causes spatial fluctuation of the local coordination number. Moreover, if there is no positional disorder, ωTIR ≈ωLIR. Therefore, the argument that the boson peak is equivalent to the transverse Ioffe-Regel limit is not general. Our results suggest that both local coordination number and positional disorder are necessary for the argument to hold, which is actually the case for most disordered solids such as marginally jammed solids and structural glasses. We further combine two types of disorders to cause disorder in both the local coordination number and lattice site position. The density of vibrational states of the resulting networks resembles that of marginally jammed solids well. However, the relation between the boson peak and the transverse Ioffe-Regel limit is still indefinite and condition-dependent. Therefore, the interplay between different types of disorders is complicated, and more in-depth studies are required to sort it out.
基金Project supported by the National Natural Science Foundation of China(52171184,51771220,51771095)the Zhejiang Provincial Natural Science Foundation of China(LD19E010001)。
文摘We report the pronounced low-temperature specific-heat Cpanomalies in the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)bulk metallic glass(BMG).The extrapolated electron’s temperature coefficientγ0Kis up to 681.8 mJ/(molGd·K^(2))at 0 K,which is a heavy-fermion-like behavior.The low temperature specific heat indicates an enhancement of the conduction-electron effective mass m*below 7.5 K,suggesting that the Mg_(59.5)Cu_(22.9)Ag_(6.6)Gd_(11)BMG is not free-electron-like solid.The excess specific heat in the Mg-based BMG is interpreted with tunneling states and spin glass state(magnetism)which are determined by subtracting electrons’and phonons’contribution to the specific heat below 12 K.The Boson peak(BP)temperature is located at 27 K,which is much higher than the reported values of other BMGs.And,a BP height of 0.047 mJ/(mol·K^(4))is obtained due to reduced free volume during copper mold casting with a slow cooling rate.The electrical resistivity was also investigated between 2 and 300 K,which has a negative temperature coefficient of resistivity(TCR)below 35 K(Kondo temperature,TK)and a positive value of 3.9×10^(-4)/K above 35 K.There is a minimum at about 35 K for the electrical resistivity,which can be explained by the Kondo effect.For the resistivity above 35 K,it can be explained by the FaberZiman model due to the T-dependence change of structure factor.
基金supported by the National Natural Science Foundation of China (Grant No.50801041)National Basic Research Program of China (Grant No.2007CB613901)Research Fund for the Doctoral Program of Higher Education of China (Grant No.200804221041)
文摘The glass transition involves more than one dynamic relaxation mechanisms in supercooled liquids,such as α relaxation,slow β relaxation and fast β relaxation and so on.For the traditional theoretical system,α relaxation is believed mainly responsible for the nature of the glass transition as the beginning of the phenomenon.This idea,however,has been open to a big challenge since recent studies have indicated that slow β relaxation closely relates to α relaxation.Slow β relaxation determines the characteristics of α relaxation and is the precursor and the more microscopic base of glass transition behavior.In order to illuminate the significance of slow β relaxation in the fields of the glass transition and the structure of supercooled liquids,the accomplished progress is summarized from different aspects such as on the correlation between α relaxation and slow β relaxation,on the manner of α-slow β relaxation merging,on the energy landscape,on the excess wing and on the thermodynamically phenomenological models.The tendency of investigation in slow β relaxation is also evaluated.
基金supported by the General Project(11972345)National Distinguished Youth Science Fund Project(12125206)Major Project(11790292)of National Natural Science Foundation of China(NSFC).
文摘Rejuvenation of glassy structures in general is characterized by the exothermic enthalpy prior to the glass transition.In the present work,we find that this situation is not applicable to a heavily-aged Zr-based metallic glass that rejuvenates by anelastic deformation before yield.Instead,its rejuvenation can be precisely captured by the low-temperature boson heat capacity peak as well as the effective enthalpy change with the glass-to-liquid transition.These results demonstrate that a structurally stable glass could rejuvenate by decreasing mechanical stability of its basin of potential energy landscape,but without changing the basin's energy level.The underlying mechanism points toward the redistribution of the atomic free volume with a constant system-averaged value.We further find that the rejuvenation limit of this glass is its steady-flow state with self-similar inherent structures at both short-and long-time scales.Our findings refresh the understanding of glass rejuvenation and suggest that the boson peak is a better probe for the structural rejuvenation of glasses.
