Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous...Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous SiO_(2)film during nanoindentation are probed using molecular dynamics simulation by varying the indenter’s size.The results show that the indentation force(stress)declines sharply at the initial and decreases almost linearly toward the end of holding for tested samples.The amount of stress relaxation of SiO_(2)/Si samples indented with different indenters during holding increases with growing indenter size,and the corresponding plastic deformation characteristics are carefully analyzed.The deformation mechanism for confined amorphous SiO_(2)film is depicted based on the amorphous plasticity theories,revealing that the more activated shear transformation zones(STZs)and free volume within indented SiO_(2)film promote stress relaxation.The phase transformation takes place to monocrystalline silicon,the generated atoms of Si-II and bct-5 phases within monocrystalline silicon substrate during holding are much higher than those for smaller indenter.展开更多
Intermittent shear flow including start-up flow and small oscillatory amplitude time sweep or stress relaxation aftercessation of shear flow was used to study the rheological behavior and internal structure of thermot...Intermittent shear flow including start-up flow and small oscillatory amplitude time sweep or stress relaxation aftercessation of shear flow was used to study the rheological behavior and internal structure of thermotropic liquid crystallinepolymer(TLCP).There are two kinds of intermittent shear flow:all start-up flows are in the same direction(intermittent flowforward:IFF)and start-up flows change their directions alternately(intermittent flow reversal:IFR).The results show thatthe stress of start-up flow of IFF and IFR in the test process is not superposed,indicating different changes of internalstructure of thermotropic LCP(TLCP).Two main factors affect structure changes in the experimental time scale.One relatesto long-term texture relaxation process,the other is an interchain reaction that becomes important after 30 min.The twofactors raise the stress of IFF,but express complex effects for the stress of IFR.The latter factor becomes very important atlong time annealing process.The relaxation behavior was also studied by the application of wide range relaxation spectrumcalculated from the combined dynamic modulus,which gave three characteristic relaxation times(0.3,10 and 600 s)ascribable to the relaxations of less-phase orientation,domain orientation,and domain deformation,respectively.The resultalso shows that the domain coalescence(texture relaxation),a long relaxation time,is a much slow process and lasts beyond2400 s of the test time.展开更多
The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coa...The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coating supports a higher saturated water content, Mχ, and helps to facilitate absorption D. The three parameters of stretched exponential function called the William-Watt equation, Eo, τ, and β, are determined to fit the degraded stress relaxation behavior in the water absorption process because this function quantitatively describes the relaxing ability and has been successfully used by a number of researchers. An increasing in the water content is shown to correlate strongly with a decrease in Eo and fl early in the absorption process between Mt/M（χ） = 0 and Mt/Mχ≈ 0.5. The adhesive characteristics of the coatings are correlated with water content, and shown to exhibit higher cohesive failure in coating epoxies under saturated conditions. This suggests that water interferes with the intermolecular bonding between polymer chains which degrades the bulk materials ability to diffuse stress concentrations and reduces its overall strength.展开更多
The linear and nonlinear magnetizations of La0.9Tb0.1MnO3 at low temperatures were reported in de- tail. The temperature dependence of magnetization shows peaks at 50, 100 and 150 K, respectively. When LaMnO3 is Tb-do...The linear and nonlinear magnetizations of La0.9Tb0.1MnO3 at low temperatures were reported in de- tail. The temperature dependence of magnetization shows peaks at 50, 100 and 150 K, respectively. When LaMnO3 is Tb-doped, its magnetic structure exhibits a canted an- tiparallel spin order. This is different from classical antiferromagnetic （AFM） in which the relaxation behavior takes place at about 150 K. At 50 K, Tb-doped LaMnO3 exhibits canonical spin glass behavior, arising from the competition of exchange and super-exchange between spins. The peak at 100 K shows neither spin glass behavior nor canted AFM behavior. Its peak value increases with frequency increasing, and the transition temperature of the peak shifts to higher temperatures with frequency increasing. The study of aging behavior at 100 K shows a periodical variable metastability, which is ascribed to the competition between ferromagnetic （FM）-, AFM- and sinusoidal-order interactions. This work should shed a light on understanding the complex magnetic structure of the perovskite oxides.展开更多
Piezoelectric materials with unique properties are hugely appealing for high sensitivity sensors and ultrasonic transducers.Here,Pb(Ni_(1/3)Nb_(2/3))O_(3)-Pb(Yb_(1/2)Nb_(1/2))O_(3)-PbTiO_(3)piezoelectric system was de...Piezoelectric materials with unique properties are hugely appealing for high sensitivity sensors and ultrasonic transducers.Here,Pb(Ni_(1/3)Nb_(2/3))O_(3)-Pb(Yb_(1/2)Nb_(1/2))O_(3)-PbTiO_(3)piezoelectric system was designed and investigated in detail.The optimized piezoelectric response(d_(33)=826 pC/N,d_(33)∗=1017 pm/V)together with good temperature stability and negligible performance degradation up to 10^(6) cycles was achieved in 0.58PNN-0.10PYN-0.32PT composition.Rayleigh analysis revealed the amplification of intrinsic and extrinsic contributions in MPB region due to more spontaneous polarization orientations and an increase in chemical disorder of system after the introduction of PYN.The origin of high piezoelectric response was investigated through the combination of scanning electron microscopy and piezoresponse force microscopy.The diversity of B-site cations was shown to enhance local structural heterogeneity,weaken long-range ferroelectric ordered domains,and lower free energy barrier via the formation of nanodomain configuration that promoted polarization rotation,thereby improving piezoelectric properties of the material.Therefore,it is suggested that increasing the diversity of B-site cations is an effective strategy for achieving outstanding piezoelectric performance.展开更多
基金the National Natural Science Foundation of China(Nos.51375364,51575372)Doctor Funds of Taiyuan University of Science and Technology(No.20202004)。
文摘Long-lasting constant loading commonly exists in silicon-based microelectronic contact and can lead to the appearance of plastic deformation.Stress relaxation behaviors of monocrystalline silicon coated with amorphous SiO_(2)film during nanoindentation are probed using molecular dynamics simulation by varying the indenter’s size.The results show that the indentation force(stress)declines sharply at the initial and decreases almost linearly toward the end of holding for tested samples.The amount of stress relaxation of SiO_(2)/Si samples indented with different indenters during holding increases with growing indenter size,and the corresponding plastic deformation characteristics are carefully analyzed.The deformation mechanism for confined amorphous SiO_(2)film is depicted based on the amorphous plasticity theories,revealing that the more activated shear transformation zones(STZs)and free volume within indented SiO_(2)film promote stress relaxation.The phase transformation takes place to monocrystalline silicon,the generated atoms of Si-II and bct-5 phases within monocrystalline silicon substrate during holding are much higher than those for smaller indenter.
基金This work was supported by the National Natural Science Foundation of China(Nos.201740242020400750290090).
文摘Intermittent shear flow including start-up flow and small oscillatory amplitude time sweep or stress relaxation aftercessation of shear flow was used to study the rheological behavior and internal structure of thermotropic liquid crystallinepolymer(TLCP).There are two kinds of intermittent shear flow:all start-up flows are in the same direction(intermittent flowforward:IFF)and start-up flows change their directions alternately(intermittent flow reversal:IFR).The results show thatthe stress of start-up flow of IFF and IFR in the test process is not superposed,indicating different changes of internalstructure of thermotropic LCP(TLCP).Two main factors affect structure changes in the experimental time scale.One relatesto long-term texture relaxation process,the other is an interchain reaction that becomes important after 30 min.The twofactors raise the stress of IFF,but express complex effects for the stress of IFR.The latter factor becomes very important atlong time annealing process.The relaxation behavior was also studied by the application of wide range relaxation spectrumcalculated from the combined dynamic modulus,which gave three characteristic relaxation times(0.3,10 and 600 s)ascribable to the relaxations of less-phase orientation,domain orientation,and domain deformation,respectively.The resultalso shows that the domain coalescence(texture relaxation),a long relaxation time,is a much slow process and lasts beyond2400 s of the test time.
文摘The kinetics of water absorption in water-borne anticorrosive urethane/epoxy coatings, which were actually introduced in the industrial field, are studied. It is found that the high water affinity of a water-borne coating supports a higher saturated water content, Mχ, and helps to facilitate absorption D. The three parameters of stretched exponential function called the William-Watt equation, Eo, τ, and β, are determined to fit the degraded stress relaxation behavior in the water absorption process because this function quantitatively describes the relaxing ability and has been successfully used by a number of researchers. An increasing in the water content is shown to correlate strongly with a decrease in Eo and fl early in the absorption process between Mt/M（χ） = 0 and Mt/Mχ≈ 0.5. The adhesive characteristics of the coatings are correlated with water content, and shown to exhibit higher cohesive failure in coating epoxies under saturated conditions. This suggests that water interferes with the intermolecular bonding between polymer chains which degrades the bulk materials ability to diffuse stress concentrations and reduces its overall strength.
基金supported by the Special Program for State Key Laboratory of Electrical Insulation and Power Equipment(No.EIPE11207)the Special Program for State Key Laboratory Breeding Base of Dielectrics Engineering(No.DE2011A01)+1 种基金the Special Program for Education Bureau of Province(No.12JK0953)the National Natural Science Foundation of China(No.51201094)
文摘The linear and nonlinear magnetizations of La0.9Tb0.1MnO3 at low temperatures were reported in de- tail. The temperature dependence of magnetization shows peaks at 50, 100 and 150 K, respectively. When LaMnO3 is Tb-doped, its magnetic structure exhibits a canted an- tiparallel spin order. This is different from classical antiferromagnetic （AFM） in which the relaxation behavior takes place at about 150 K. At 50 K, Tb-doped LaMnO3 exhibits canonical spin glass behavior, arising from the competition of exchange and super-exchange between spins. The peak at 100 K shows neither spin glass behavior nor canted AFM behavior. Its peak value increases with frequency increasing, and the transition temperature of the peak shifts to higher temperatures with frequency increasing. The study of aging behavior at 100 K shows a periodical variable metastability, which is ascribed to the competition between ferromagnetic （FM）-, AFM- and sinusoidal-order interactions. This work should shed a light on understanding the complex magnetic structure of the perovskite oxides.
基金supported by the National Natural Science Foundation of China(No.52173227)the Key Research and Development Program of Shaanxi(No.2022GY-184)the Innovation Fund of Xidian University,and the Fundamental Research Funds for the Central Universities(No.ZYTS23083).
文摘Piezoelectric materials with unique properties are hugely appealing for high sensitivity sensors and ultrasonic transducers.Here,Pb(Ni_(1/3)Nb_(2/3))O_(3)-Pb(Yb_(1/2)Nb_(1/2))O_(3)-PbTiO_(3)piezoelectric system was designed and investigated in detail.The optimized piezoelectric response(d_(33)=826 pC/N,d_(33)∗=1017 pm/V)together with good temperature stability and negligible performance degradation up to 10^(6) cycles was achieved in 0.58PNN-0.10PYN-0.32PT composition.Rayleigh analysis revealed the amplification of intrinsic and extrinsic contributions in MPB region due to more spontaneous polarization orientations and an increase in chemical disorder of system after the introduction of PYN.The origin of high piezoelectric response was investigated through the combination of scanning electron microscopy and piezoresponse force microscopy.The diversity of B-site cations was shown to enhance local structural heterogeneity,weaken long-range ferroelectric ordered domains,and lower free energy barrier via the formation of nanodomain configuration that promoted polarization rotation,thereby improving piezoelectric properties of the material.Therefore,it is suggested that increasing the diversity of B-site cations is an effective strategy for achieving outstanding piezoelectric performance.
