F.Y. Meng

Lattice, elastic, polarization, and electrostrictive properties of BaTiO3 from first-principles

Predicting the domain structures and properties in both bulk single crystal and thin film ferroelectrics using the phase-field approach requires the knowledge of fundamental mechanical, electrical, and electromechanical coupling properties of a single-domain state. In this work, the elastic properties and structural parameters of cubic single crystals as well as tetragonal, orthorhombic, and rhombohedral BaTiO3 single domain states are obtained using first-principles calculations under the local density approximation. The calculated lattice constants, bulk modulus, and elastic constants are in good agreement with experiments for both the cubic paraelectric phase and the low-temperature ferroelectric phases. Spontaneous polarizations for all three ferroelectric phases and the electrostrictive coefficients of cubic BaTiO3 are also computed using the Berry’s phase approach, and the results agree well with existing experimentally measured values.

Micromagnetic simulation of spin-transfer switching in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar

We investigated the spin-transfer switching in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar through micromagnetic simulation. A two-step switching hysteresis loop due to the fourfold in-plane magnetocrystalline anisotropy of Co2FeAl0.5Si0.5 layers was obtained. The simulation explains the experimental result of the resistance versus current hysteresis loop and yields good agreement with the measured critical current. Furthermore, the magnetization trajectory and magnetization distribution were shown and analyzed to elucidate the different characters of two-step switching.

The thermal conductivity of carbon nanotubes with defects and intramolecular junctions

The thermal conductivity of various carbon nanotubes with defects or intramolecular junctions was studied using nonequilibrium molecular dynamics approach. The results show that the thermal conductivity of both armchair and zigzag carbon nanotubes increased with the decrease of the radius of the tube. The thermal conductivity of armchair tube is higher than that of zigzag tube when the radii of the two tubes are kept almost same. Discontinuities appear on the temperature profile along the tube axial at the region of IMJ, resulting in the large temperature gradient and thus lower thermal conductivity of (n, n)/(m, 0) tube with one IMJ and (m, 0)/(n, n)/(m, 0) tube with two IMJs. For the (m, 0)/(n, n)/(m, 0) tube with two IMJs, phonon mean free path of the middle (n, n) tube is much smaller than that of the isolate (n, n) tube.

Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.g. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI resulting in SCC.

First-Principle study on the interaction between Fe and trivacancy in graphene

Ab initio calculations using density functional theory (DFT) have been performed in order to explore structure and energy gap opening of graphene with bridged-trivacancy and single adsorbed with Fe atom. Compared to the previous reconstructed trivacancy adsorbed with Fe atom with the energy gap of 0.10 eV, one interesting structure for the Fe-doped bridged-trivacancy complex has been identified, with one Fe atom above the graphene plane, and possesses energy gap with the value of 0.32 eV in the bridged circumstance. The band gap can be explained by the decrease of the free electrons. These results provide insights to engineer graphenes properties through defect addition and manipulation for industrial semiconductor applications such as the photocatalytic technology and graphene based electronics.