Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback co...Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback control on nuclear spin precession in a metastability exchange optical pumping(MEOP)-based polarized^(3)He system.We analyze the effects of feedback theoretically and validate our predictions experimentally.With optimized feedback parameters,the spin coherence time T_(2)is extended by an order of magnitude.When the feedback strength surpasses a critical threshold,robust maser oscillations are spontaneously excited,demonstrating remarkable resistance to environmental noise and maintaining stable oscillation.This proof-of-principle experiment highlights the viability of MEOP-based^(3)He spin oscillators,especially in low-frequency domains.The operational simplicity and easy integration associated with MEOP-based systems make them particularly promising for fast,high-precision magnetic field measurements.展开更多
In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable...In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable states and free energy of the model are investigated. The states are defined in terms of local minima of the free energy of system. The numerical calculations are presented for several values of exchange interactions on the simple cubic lattice with q = 6.展开更多
This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of m...This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.展开更多
The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-p...The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-phase field forging of the cast ingot exhibits uniform composition distribution on its cross-section.However,various degrees of deformation are detected at different positions on the cross-section,which is attributed to the characteristics of the forging process.Under the forging condition,the microstructure is mainly composed ofβ-phase matrix and coarsened discontinuous primaryα-phases.After solution and following artificial aging treatment,the primaryα-phases disappear,while needle-like secondaryα-phases precipitate in the matrix.Additionally,dispersed white zones are observed in the samples after aging,which are analyzed to be the precipitation-free zones of secondaryα-phase.Despite a uniform compositional distribution among various regions,these dispersed white zones exhibit higher content and larger size in the positions that have undergone lower forging deformation.It indicates that the insufficient forging deformation inhibits the precipitation of the secondaryα-phase,ultimately resulting in the lower strengthening effect by heat treatment.Thus,consistent with the characteristics of the forging process,a periodic variation of sample in strength is detected along the circumferential direction of the forged round bar.展开更多
High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transit...High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transition kinetics remain poorly understood.Here,we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β-Sn Ge under rapid decompression at different rates.High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures:an almost perfect st12 Ge crystal,nanosized bc8/r8 structures with amorphous boundaries,and amorphous Ge with nanosized clusters (0.8–2.5 nm).Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate,temperature,and stress.This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.展开更多
Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study use...Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study uses molecular dynamics(MD)simulations to investigate the interactions between two quartz plates separated by a water film,focusing on the relationship between adhesion force and separation distance.The density and orientation angle profiles were calculated from simulation data to investigate the relationship between the interfacial structure of the water film and contact potential.The simulations reveal multiple metastable states of the contact potential,consistent with existing theoretical models.The results show that the contact force is influenced by the structure of the water film,including oscillation forces and stratification.This provided verification and development for existing theoretical models based on metastable contacts.展开更多
The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)M...The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.展开更多
TiAl alloys with the(α2+γ)lamellar structure are highly valued for their excellent high-temperature strength and creep resistance.Understanding the formation mechanism of the lamellar structure is crucial for tuning...TiAl alloys with the(α2+γ)lamellar structure are highly valued for their excellent high-temperature strength and creep resistance.Understanding the formation mechanism of the lamellar structure is crucial for tuning the microstructure and properties.This work investigates the formation of lamellar structure in Ti-48AI-7Nb-2.5V-1Cr alloy,revealing the presence of hcp-based long-period superstructure(hcp-LPS)as a metastable phase during lamellar formation.The identification of hcp-LPS demonstrates that the necessary solute enrichment for the formation ofγlamellae occurs on the hexagonalαmatrix,implying that phase separation ofα→Al-richαlamellae+Al-depletedαlamellae is the first step of lamellar formation.Once phase separation is completed,all subsequent phase transitions occur within the Al-richαlamellae.Additionally,the formation of twin lamellae is further discussed.The formation of the twin lamellae occurs sequentially.Pre-existing lamella promotes the formation of later lamella by inducing so-lute enrichment in its surrounding region,and then the successive slip of Shockley partial dislocations with opposite Burgers vectors ensures special stacking of later lamellae.These findings not only con-tribute to the fundamental understanding of spinodal mechanisms in hexagonal crystals,but also provide novel insights into the formation of twin lamellae.展开更多
The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures...The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures and electronic properties are essential,and phase engineering provides a transformative approach by modulating crystallographic symmetry and electronic configurations.Two-dimensional(2D)LaMnO_(3) perovskites show promise due to their exposed active sites and tunable electronic properties.However,the conventional stable rhombohedral phase limits oxygen diffusion despite good electron transport.Unconventional metastable phases with superior symmetry enhance lattice oxygen activity in saline environments but are challenging to synthesize.Herein,we propose a microwave shock method incorporating Co atoms to rapidly produce 2D LaMnO_(3) in rhombohedral,hexagonal,and metastable cubic phases.This strategy circumvents the limitations of high-temperature synthesis,preserving the 2D morphology while enabling the formation of metastable cubic phases.The metastable cubic phase exhibits superior OER activity and stability even in alkaline seawater due to optimal symmetry,interlayer spacing,and Mn-O covalency.X-ray absorption spectroscopy and theoretical calculations further highlight its balanced oxygen adsorption and desorption.This work underscores the role of metastable phase engineering in advancing seawater electrolysis and establishes a scalable route for designing high-performance 2D electrocatalysts.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.U2230207)。
文摘Achieving long spin coherence times is crucial for quantum precision measurements,and closed-loop control techniques are often employed to accomplish this goal.Here,we demonstrate the impact of closed-loop feedback control on nuclear spin precession in a metastability exchange optical pumping(MEOP)-based polarized^(3)He system.We analyze the effects of feedback theoretically and validate our predictions experimentally.With optimized feedback parameters,the spin coherence time T_(2)is extended by an order of magnitude.When the feedback strength surpasses a critical threshold,robust maser oscillations are spontaneously excited,demonstrating remarkable resistance to environmental noise and maintaining stable oscillation.This proof-of-principle experiment highlights the viability of MEOP-based^(3)He spin oscillators,especially in low-frequency domains.The operational simplicity and easy integration associated with MEOP-based systems make them particularly promising for fast,high-precision magnetic field measurements.
文摘In this paper, the equilibrium properties of spin-1 Blume–Emery–Griffiths model are studied by using constant-coupling approximation. The dipolar and quadrupolar order parameters, the stable, metastable and unstable states and free energy of the model are investigated. The states are defined in terms of local minima of the free energy of system. The numerical calculations are presented for several values of exchange interactions on the simple cubic lattice with q = 6.
文摘This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.
基金Qin Chuangyuan Cites High-Level Innovation,Entrepreneurship Talent Project(QCYRCXM-2023-003)Innovation Capability Support Program of Shaanxi(2022KJXX-84)。
文摘The effect of hot deformation onα-phase precipitation during the subsequent heat treatment,as well as the mechanical properties of TB18 Ti-alloy,was investigated.Results show that the round bar obtained by the dual-phase field forging of the cast ingot exhibits uniform composition distribution on its cross-section.However,various degrees of deformation are detected at different positions on the cross-section,which is attributed to the characteristics of the forging process.Under the forging condition,the microstructure is mainly composed ofβ-phase matrix and coarsened discontinuous primaryα-phases.After solution and following artificial aging treatment,the primaryα-phases disappear,while needle-like secondaryα-phases precipitate in the matrix.Additionally,dispersed white zones are observed in the samples after aging,which are analyzed to be the precipitation-free zones of secondaryα-phase.Despite a uniform compositional distribution among various regions,these dispersed white zones exhibit higher content and larger size in the positions that have undergone lower forging deformation.It indicates that the insufficient forging deformation inhibits the precipitation of the secondaryα-phase,ultimately resulting in the lower strengthening effect by heat treatment.Thus,consistent with the characteristics of the forging process,a periodic variation of sample in strength is detected along the circumferential direction of the forged round bar.
基金supported by the National Nature Science Foundation of China(NSFC)(Grant No.11974033)Xuqiang Liu acknowledges support from the National Postdoctoral Foundation Project of China under Grant No.GZC20230215+2 种基金the National Nature Science Foundation of China under Grants No.12404001The XRD measurements at room and high temperatures were performed at the 4W2 HPStation of the Beijing Synchrotron Radiation Facility(BSRF)and beamline 15U1 of the Shanghai Synchrotron Radiation Facility(SSRF)In situ high-pressure,low-temperature XRD measurements were conducted at sector 16 ID-B,HPCAT of the Advanced Photon Source,and were supported by DOE-NNSA under Award No.DE-NA0001974.
文摘High-pressure β-Sn germanium may transform into diverse metastable allotropes with distinctive nanostructures and unique physical properties via multiple pathways under decompression.However,the mechanism and transition kinetics remain poorly understood.Here,we investigate the formation of metastable phases and nanostructures in germanium via controllable transition pathways of β-Sn Ge under rapid decompression at different rates.High-resolution transmission electron microscopy reveals three distinct metastable phases with the distinctive nanostructures:an almost perfect st12 Ge crystal,nanosized bc8/r8 structures with amorphous boundaries,and amorphous Ge with nanosized clusters (0.8–2.5 nm).Fast in situ x-ray diffraction and x-ray absorption measurements indicate that these nanostructured products form in certain pressure regions via distinct kinetic pathways and are strongly correlated with nucleation rates and electronic transitions mediated by compression rate,temperature,and stress.This work provides deep insight into the controllable synthesis of metastable materials with unique crystal symmetries and nanostructures for potential applications.
文摘Laboratory and field observations have suggested a correlation between contact dynamics and slow dynamics.The underlying mechanical mechanisms at the contact level require investigation at the nanoscale.This study uses molecular dynamics(MD)simulations to investigate the interactions between two quartz plates separated by a water film,focusing on the relationship between adhesion force and separation distance.The density and orientation angle profiles were calculated from simulation data to investigate the relationship between the interfacial structure of the water film and contact potential.The simulations reveal multiple metastable states of the contact potential,consistent with existing theoretical models.The results show that the contact force is influenced by the structure of the water film,including oscillation forces and stratification.This provided verification and development for existing theoretical models based on metastable contacts.
基金financial support by the National Natural Science Foundation of China(No.51364032)the Inner Mongolia Natural Science Foundation(No.2022MS05028)。
文摘The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.
基金supported by the National Science and Technology Major Project of China(No.J2019-VI-0011-0125)ND Basic Research Funds of China(No.G2022WD)Shaanxi Province Innovation Capability Support Program(No.2023-CX-TD-47).
文摘TiAl alloys with the(α2+γ)lamellar structure are highly valued for their excellent high-temperature strength and creep resistance.Understanding the formation mechanism of the lamellar structure is crucial for tuning the microstructure and properties.This work investigates the formation of lamellar structure in Ti-48AI-7Nb-2.5V-1Cr alloy,revealing the presence of hcp-based long-period superstructure(hcp-LPS)as a metastable phase during lamellar formation.The identification of hcp-LPS demonstrates that the necessary solute enrichment for the formation ofγlamellae occurs on the hexagonalαmatrix,implying that phase separation ofα→Al-richαlamellae+Al-depletedαlamellae is the first step of lamellar formation.Once phase separation is completed,all subsequent phase transitions occur within the Al-richαlamellae.Additionally,the formation of twin lamellae is further discussed.The formation of the twin lamellae occurs sequentially.Pre-existing lamella promotes the formation of later lamella by inducing so-lute enrichment in its surrounding region,and then the successive slip of Shockley partial dislocations with opposite Burgers vectors ensures special stacking of later lamellae.These findings not only con-tribute to the fundamental understanding of spinodal mechanisms in hexagonal crystals,but also provide novel insights into the formation of twin lamellae.
文摘The electrolysis of alkaline seawater is critical for sustainable hydrogen production but is hindered by the sluggish oxygen evolution reaction in saline environments.Advanced electrocatalysts with tailored structures and electronic properties are essential,and phase engineering provides a transformative approach by modulating crystallographic symmetry and electronic configurations.Two-dimensional(2D)LaMnO_(3) perovskites show promise due to their exposed active sites and tunable electronic properties.However,the conventional stable rhombohedral phase limits oxygen diffusion despite good electron transport.Unconventional metastable phases with superior symmetry enhance lattice oxygen activity in saline environments but are challenging to synthesize.Herein,we propose a microwave shock method incorporating Co atoms to rapidly produce 2D LaMnO_(3) in rhombohedral,hexagonal,and metastable cubic phases.This strategy circumvents the limitations of high-temperature synthesis,preserving the 2D morphology while enabling the formation of metastable cubic phases.The metastable cubic phase exhibits superior OER activity and stability even in alkaline seawater due to optimal symmetry,interlayer spacing,and Mn-O covalency.X-ray absorption spectroscopy and theoretical calculations further highlight its balanced oxygen adsorption and desorption.This work underscores the role of metastable phase engineering in advancing seawater electrolysis and establishes a scalable route for designing high-performance 2D electrocatalysts.
