查看更多>>摘要：Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems.The search for refrigeration materials displaying a unique combination of pronounced caloric effect,low hysteresis,and high reversibility on phase transformation was very active in recent years.Here,we achieved increase in the elastocaloric reversibility and decrease in the friction dissipation of martensite transformations in the superelastic nano-grained NiTi alloys obtained by cold rolling and annealing treatment,with very low stress hysteresis(6.3 MPa)under a large applied strain(5％).Large adiabatic temperature changes(△Tmax=16.3 K at ε=5％)and moderate COPmater values(maximum COPmater=11.8 at ε=2％)were achieved.The present nano-grained NiTi alloys exhibited great potential for applications as a highly efficient elastocaloric material.
查看更多>>摘要：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.
查看更多>>摘要：Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi0.7Sb0.3)2Te3 nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle-dependent HDPC,it is found that the HDPC is mainly contributed by the circular photogalvanic effect(CPGE)current when the incident plane is perpendicular to the connection of the two contacts,whereas the circular photon drag effect(CPDE)dominates the HDPC when the incident plane is parallel to the connection of the two contacts.In addition,the CPGE of the(Bi0.7Sb0.3)2Te3 nanoplate is regulated by temperature,light power,excitation wavelength,the source-drain and ionic liquid top-gate volt-ages,and the regulation mechanisms are discussed.It is demonstrated that(Bi0.7Sb0.3)2Te3 nanoplates may provide a good platform for novel opto-spintronics devices.
查看更多>>摘要：Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling.These two properties,however,hardly coexist in single phase materials except previously reported hexagonal Cr1-xTe half metal where a relatively high magnetic entropy change(-△SM)of～2.4 J.kg-1·K-1@5 T and a moderate thermoelectric figure of merit(ZT)of～1.2 × 10-2@300 K are simultaneously recorded.Herein we aim to increase the thermoelectric performance of Cr1-xTe by compositing with semiconducting Ag2Te.It is discovered that the in-situ synthesis of Cr1-xTe/Ag2Te composites by reacting their constitute elements above melting temperatures is unsuccessful because of strong phase competition.Specifically,at elevated temperatures(T＞800 K),Cr1-xTe has a much lower deformation energy than Ag2Te and tends to become more Cr-deficient by capturing Te from Ag2Te.Therefore,Ag is insufficiently reacted and as a metal it deteriorates ZT.We then rationalize the synthesis of Cr1-xTe/Ag2Te composites by ex-situ mix of the pre-prepared Cr1-xTe and Ag2Te binary compounds followed by densification at a low sintering temperature of 573 K under a pressure of 3.5 GPa.We show that by compositing with 7 mol％Ag2Te,the Seebeck coefficient of Cr1-xTe is largely increased while the lattice thermal conductivity is considerably reduced,leading to 72％improvement of ZT.By comparison,-△SM is only slightly reduced by 10％in the composite.Our work demonstrates the potential of Cr1-xTe/Ag2Te composites for thermoelectromagnetic cooling.
查看更多>>摘要：We utilize the calculation of hierarchical equations of motion to demonstrate that the spin-dependent properties be-tween adjacent quantum dots(QDs)can be changed by breaking the internal symmetry configuration,corresponding to the inversion of dominant chiral states.In the linear triple quantum dots(LTQDs)connected to two electron reservoirs,we can observe that the blockage appears at the triangle triple quantum dots(TTQDs)by gradually increasing the coupling strength between next-nearest double QDs.When the initial coupling between LTQDs has altered,the internal chiral cir-culation also undergoes the corresponding transform,thus achieving qualitative regulation and detection of the blocking region.We also investigate the response of the chiral circulation to the dot-lead coupling strength,indicating the overall robust chiral circulation of the TTQDs frustration.
查看更多>>摘要：The first-principles calculations are performed to examine structural,mechanical,and electronic properties at large strain for a monolayer C4N4,which has been predicted as an anchoring promising material to attenuate shuttle effect in Li-S batteries stemming from its large absorption energy and low diffusion energy barrier.Our results show that the ideal strengths of C4N4 under tension and pure shear deformation conditions reach 13.9 GPa and 12.5 GPa when the strains are 0.07 and 0.28,respectively.The folded five-membered rings and diverse bonding modes between carbon and nitrogen atoms enhance the ability to resist plastic deformation of C4N4.The orderly bond-rearranging behaviors under the weak tensile loading path along the[100]direction cause the impressive semiconductor-metal transition and inverse semiconductor-metal transition.The present results enrich the knowledge of the structure and electronic properties of C4N4 under deformations and shed light on exploring other two-dimensional materials under diverse loading conditions.
查看更多>>摘要：Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity(RC)was reported.Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K.In addition,we find that the magnetic entropy change(-△SM)originates from the sample undergoing a ferromagnetic(FM)to paramagnetic(PM)transition around 20 K.Under a field change from 0 T to 7 T,the value of maximum magnetic entropy change(-△.SmaxM)reaches 12.5 J/kg·K,and the corre-sponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K.The large RC and wide temperature range make the Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass be a promising material for application in magnetic refrigerators.
查看更多>>摘要：Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric properties.New Bi-based perovskite thin films Bi(Cu1/2Ti1/2)O3-PbTiO3(BCT-PT)are deposited on Pt(111)/Ti/SiO2/Si substrates in the present study by the traditional sol-gel method.Their structures and related ferro-electric and fatigue characteristics are studied in-depth.The BCT-PT thin films exhibit good crystallization within the phase-pure perovskite structure,besides,they have a predominant(100)orientation together with a dense and homoge-neous microstructure.The remnant polarization(2Pr)values at 30 μC/cm2 and 16 μC/cm2 are observed in 0.1BCT-0.9PT and 0.2BCT-0.8PT thin films,respectively.More intriguingly,although the polarization values are not so high,0.2BCT-0.8PT thin films show outstanding polarization fatigue properties,with a high switchable polarization of 93.6％of the starting values after 108 cycles,indicating promising applications in ferroelectric memories.
查看更多>>摘要：Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted mag-netic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn)and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant-dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,super-exchange and Zener's p-d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.
查看更多>>摘要：Combining the first-principles calculations and structural enumeration with recognition,the delithiation process of LiNiO2 is investigated,where various supercell shapes are considered in order to obtain the formation energy of LixNiO2.Meanwhile,the voltage profile is simulated and the ordered phases of lithium vacancies corresponding to concentrations of 1/4,2/5,3/7,1/2,2/3,3/4,5/6,and 6/7 are predicted.To understand the capacity decay in the experiment during the charge/discharge cycles,deoxygenation and Li/Ni antisite defects are calculated,revealing that the chains of oxygen vacancies will be energetically preferrable.It can be inferred that in the absence of oxygen atom in high delithiate state,the diffusion of Ni atoms is facilitated and the formation of Li/Ni antisite is induced.
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