Graphene/hexagonal boron nitride (h-BN) van der Waals (vdW) heterostructure has aroused great interest because of the unique Moiré pattern. In this study, we use molecular dynamics simulation to ...investigate the influence of the interlayer rotation angle θ on the interfacial thermal transport across graphene/h-BN heterostructure. The interfacial thermal conductance G of graphene/h-BN interface reaches 509 MW/(m2K) at 500 K without rotation, and it decreases monotonically with the increase of the rotation angle, exhibiting around 50% reduction of G with θ = 26.33°. The phonon transmission function reveals that G is dominantly contributed by the low-frequency phonons below 10 THz. Upon rotation, the surface fluctuation in the interfacial graphene layer is enhanced, and the transmission function for the low-frequency phonon is reduced with increasing θ, leading to the rotation angle-dependent G. This work uncovers the physical mechanisms for controlling interfacial thermal transport across vdW heterostructure via interlayer rotation.
One of the greatest obstacles to the real application of solid-state refrigeration is the huge driving fields. Here, we report a giant barocaloric effect in inorganic NH
I with reversible entropy ...changes of Formula: see text ∼71 J K
kg
around room temperature, associated with a structural phase transition. The phase transition temperature, T
, varies dramatically with pressure at a rate of dT
/dP ∼0.79 K MPa
, which leads to a very small saturation driving pressure of ΔP ∼40 MPa, an extremely large barocaloric strength of Formula: see text ∼1.78 J K
kg
MPa
, as well as a broad temperature span of ∼41 K under 80 MPa. Comprehensive characterizations of the crystal structures and atomic dynamics by neutron scattering reveal that a strong reorientation-vibration coupling is responsible for the large pressure sensitivity of T
. This work is expected to advance the practical application of barocaloric refrigeration.
Recently, increasing efforts are being made to control thermal transport
via
coherent phonons in periodic phononic structures; however, the direct observation of coherent phonon transport is ...experimentally very difficult at ambient temperature, and the importance of coherent phonons to the total thermal conductivity has not been critically assessed to date. In this study, using the non-equilibrium molecular dynamics simulations, we studied coherent phonon transport in a C
3
N phononic crystal (CNPnC) structure at room temperature by changing the porosity. When the holes were randomly distributed to construct the disordered C
3
N (D-C
3
N) structure, the localization of the coherent phonons was revealed by the phonon transmission coefficient, phonon wave packet simulation, phonon participation ratio and spatial energy density, which led to a significant reduction in the thermal conductivity. Finally, the effects of the length, temperature and strain on the thermal conductivity of CNPnC and D-C
3
N have also been discussed. Our study provides a solid understanding of the coherent phonon transport behavior, which will be beneficial for phononic-related control based on coherent phonons.
κ
CNPnC
showed a non-monotonic dependence on porosity, and the localization of coherent phonons induced a substantial suppression of
κ
D-C
3
N
.
Refrigeration is of vital importance for modern society-for example, for food storage and air conditioning-and 25 to 30 per cent of the world's electricity is consumed for refrigeration
. Current ...refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential
. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades
. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies.
(Bi0.5Na0.5)TiO3–BiAlO3 lead‐free materials exhibit excellent ferroelectric properties, but its depolarization temperature is relatively low which is the major obstacle limiting the material's ...practical application. In this study, the effects of Manganese (Mn) modification on the microstructure, ferroelectric properties and depolarization behavior of 0.96(Bi0.5Na0.5)(Ti1−xMnx)O3–0.04BiAlO3 ceramics were investigated. It was found that the average grain size was enlarged and ferroelectric properties were enhanced with small Mn addition, meanwhile the tangent loss decreased. The remnant polarization (Pr) of the samples reached an optimal value (~41 μC/cm2) as Mn content increased up to 0.7 mol%, whereas further addition resulted in the decrease in Pr. Moreover, appropriate Mn addition (x=0.7%) can improve the depolarization temperature from 140°C to 161°C determined from thermally stimulated depolarization currents measurement.
AbstractTo reduce the rate of collision accidents between mobile cranes and immobile obstacles in construction sites during lift operations, this paper develops a real-time automated anticollision ...system that can warn crane operators about potential collisions and automatically implement collision-avoidance strategies. This system does not require additional devices and can be installed in existing crane controllers. Before the lift operation, the location and shape data of all immobile objects in the work area are collected by a boom head and stored in track-sector database of the system based on the position parameters of the boom head. During the operation of the lift, the proposed system calculates a three-dimensional safe zone for the crane, including boom, cable, and lift object based on the object data in real time, and the movement and position of the crane including boom, cable, and lift object are consistently monitored and predicted in real time through weighted linear-regression models. If the predicted position of the crane is reaching the boundary of the precalculated safety operation zone, three different levels of decelerations and an emergency stop will be automatically executed in order, according to the distance between crane and the obstacles, by the lifting controller to prevent the crane from potential collisions with immobile obstacles. A tentative application of this real-time anticollision system at real construction sites has demonstrated its ability to prevent collisions between cranes and immobile obstacles in work zones during lift operations.
The control of thermal waves by the phononic crystal exhibits peculiar behaviors different from the particle picture of phonons and thus has attracted increasing interest. However, the wave nature of ...phonons is only indirectly reflected in most studies via the macroscopic thermal transport coefficient, such as thermal conductivity. In this work, we investigate directly the coherent interference effect in a graphene superlattice structure at the microscopic phonon mode level via wave-packet simulations. The constructive interference and destructive interference between the reflected phonons give rise to valleys and peaks in the transmission coefficient, respectively, leading to the periodic oscillation of the transmission function with the variation of the superlattice period length. More importantly, both total-transmission and total-reflection of individual phonons have been clearly demonstrated. The physical conditions for realizing the phonon interference have been proposed, which are quantitatively in good agreement with independent wave-packet simulations. Our study provides direct evidence for the coherent phonon interference effect, which might be helpful for the regulation of phonon transport based on its wave nature.
We report anisotropic magnetocaloric effect and magnetoresistance in antiferromagnetic HoNiGe3 single crystal grown by Ge flux method. HoNiGe3 single crystal exhibits antiferromagnetic order and ...large magnetocrystalline anisotropy below the Néel temperature TN = 10.5 K. Meanwhile, with increasing the magnetic field, HoNiGe3 undergoes the spin-flip transition induced by the magnetic field along the a axis, while the spin-flop transition occurs for the field along the other orientations, which gives rise to anisotropic magnetoresistance behavior along three axes. With the magnetic field change of 0–50 kOe, the maximum magnetic entropy changes obtained along the a, b, and c axes are −13.9, 2.5 and −7.7 J kg−1K−1, respectively. The maximum rotating magnetic entropy change is −12.3 J kg−1K−1 under 50 kOe by rotating the magnetic field from the b axis to the a axis, and the corresponding refrigeration capacity is 193 J/kg, which demonstrates HoNiGe3 to be an attractive candidate for novel rotating magnetic refrigeration at low temperature region.
•Field-induced spin-flip and -flop transition is observed in HoNiGe3 single crystal.•Large rotating magnetocaloric effect is obtained in HoNiGe3 single crystal.•Magnetoresistance related to the spin-flip and -flop transitions is observed.
Single-crystalline Bi2Fe4O9 nanocrystals (NCs) of various sizes (from 78 to 14 nm), synthesized using the sol–gel method, exhibit size-dependent magnetic properties, which can be attributed to the ...uncompensated spins on the surface of the antiferromagnetic NCs. These tunable magnetic properties have a profound significance and can be widely applied in spintronics. As the crystal size decreases, the energy gap of the Bi2Fe4O9 semiconductor NCs increases from 1.91 to 2.04 eV, which results from quantum confinement effect. The Bi2Fe4O9 NCs exhibit excellent photocatalytic oxidation of methylene blue (MB) under visible light irradiation with the assistance of a small amount of H2O2. Interestingly, smaller NCs exhibit higher photocatalytic activities. The size-dependence of photocatalytic properties of the Bi2Fe4O9 NCs was ascribed to the lower recombination rate of the photogenerated electron/hole pair within smaller NCs and higher specific surface areas, which allow for stronger photon absorption on the surface of smaller crystals.
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