Based on first principles calculations and self-consistent solution of the linearized Boltzmann-Peierls equation for phonon transport approach within a three-phonon scattering framework, we characterize lattice thermal conductivities k of freestanding silicene, germanene and stanene under different isotropic tensile strains and temperatures. We find a strong size dependence of k for silicene with tensile strain, i.e., divergent k with increasing system size; however, the intrinsic room temperature k for unstrained silicene converges with system size to 19.34 W m(-1) K(-1) at 178 nm. The room temperature k of strained silicene becomes as large as that of bulk silicon at 84 μm, indicating the possibility of using strain in silicene to manipulate k for thermal management. The relative contribution to the intrinsic k from out-of-plane acoustic modes is largest for unstrained silicene, ∼39% at room temperature. The single mode relaxation time approximation, which works reasonably well for bulk silicon, fails to appropriately describe phonon thermal transport in silicene, germanene and stanene within the temperature range considered. For large samples of silicene, k increases with tensile strain, peaks at ∼7% strain and then decreases with further strain. In germanene and stanene, increasing strain hardens and stabilizes long wavelength out-of-plane acoustic phonons, and leads to similar k behaviors to those of silicene. These findings further our understanding of phonon dynamics in group-IV buckled monolayers and may guide transfer and fabrication techniques for these freestanding samples and engineering of k by size and strain for applications of thermal management and thermoelectricity.

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The electrocaloric effect of BaTiO 3 multilayer thick film structure was investigated by direct measurement and theoretical calculation. The samples were prepared by the tape-casting method, which had 180 dielectric layers with an average thickness of 1.4μm. The thermodynamic calculation based on the polarizationtemperature curves predicted a peak heat adsorption of 0.32J/g at 80 o C under 176kV/cm electric field. The direct measurement via differential scanning calorimeter showed a much higher electrocaloric effect of 0.91J/g at 80 o C under same electric field. The difference could result from the different trends of changes of electric polarization and lattice elastic energy under ultrahigh electric field.

Two-dimensional (2D) piezoelectric materials have gained considerable attention since they could play important roles in the nanoelectromechanical systems. Herein, we report a firstprinciples study on the piezoelectric properties of monolayer group-V binary compounds with theoretically stable honeycomb phases (αphase and β-phase). Our calculations for the first time reveal that a majority of the monolayers possess extremely high piezoelectric coefficients d 11 , i.e., 118.29, 142.44, and 243.45 pm/V for α-SbN, α-SbP, and α-SbAs, respectively, comparable to those of recently reported group-IV monochalcogenides (d 11 = 75−250 pm/V) with an identical mm2 symmetry. It is found that the giant piezoelectric responses of α-phase monolayers as compared to those of β-phase monolayers are induced by their flexible structures and special symmetry. Meanwhile, the piezoelectric coefficients of α-phase monolayers are found to be surprisingly anisotropic and obey a unique periodic trend which is not exactly identical to that for the β-phase monolayers. To gain a comprehensive understanding of the periodic trends in piezoelectricity, several factors which influence the piezoelectric coefficients are quantitatively determined.

HIGHLIGHTS • WS 2-rGO nanosheets with ultra-small thicknesses and ultra-lightweight, were successfully prepared by a facile hydrothermal method. • The WS 2-rGO isomorphic heterostructures exhibited remarkable microwave absorption properties. ABSTRACT Two-dimensional (2D) nanomaterials are categorized as a new class of microwave absorption (MA) materials owing to their high specific surface area and peculiar electronic properties. In this study, 2D WS 2-reduced graphene oxide (WS 2-rGO) heterostructure nanosheets were synthesized via a facile hydrothermal process; moreover, their dielectric and MA properties were reported for the first time. Remarkably, the maximum reflection loss (RL) of the sample-wax composites containing 40 wt% WS 2-rGO was − 41.5 dB at a thickness of 2.7 mm; furthermore, the bandwidth where RL < − 10 dB can reach up to 13.62 GHz (4.38-18 GHz). Synergistic mechanisms derived from the interfacial dielectric coupling and multiple-interface scattering after hybridization of WS 2 with rGO were discussed to explain the drastically enhanced microwave absorption performance. The results indicate these lightweight WS 2-rGO nanosheets to be potential materials for practical electromagnetic wave-absorbing applications.