Although Fe 3 O 4 particles have exhibited excellent microwave absorbing capacity and widely used in practical application due to the synergistic effect of magnetic loss and dielectric loss, their applications are still limited for the required high mass fraction in absorbers. To overcome this problem, the development of Fe 3 O 4 materials with low dimensional structures is necessary. In this study, the shape anisotropic Fe 3 O 4 nanotubes (NTs) with low mass ratios were applied to realize efficient microwave absorption. The NTs with different aspect ratios were prepared through facile electrospinning followed by two-step thermal treatments and mechanical shearing. The cross-linked nanotubular structure enabled the absorbers to have much higher electrical conductivity, multiple scattering, polarization relaxation and better anti-reflection surface, while the shape anisotropic NTs maintained significant multiple resonances with stronger coercivity. These all were beneficial to microwave absorption with enhanced dielectric loss, magnetic loss and sterling impedance matching. Results showed that the absorber with 33.3 wt.% of short Fe 3 O 4 NTs had minimum reflection loss of −58.36 dB at 17.32 GHz with a thickness of 1.27 mm, and had the maximum effective absorbing bandwidth (EAB) of 5.27 GHz when the thickness was 1.53 mm. The absorber with 14.3 wt.% of long Fe 3 O 4 NTs presented the widest EAB in certain radar band with attenuated 80.75% X band and 85% Ku band energy bellow −10 dB at the thickness of 2.65 and 1.53 mm, respectively. This study provided an approach for the development of shape anisotropic magnetic absorbing materials, and broadened their practical applications as magnetic absorbers.

In gas phase synthesis systems, clusters form and grow via condensation, in which a monomer binds to an existing cluster. While a hard-sphere equation is frequently used to predict the condensation rate coefficient, this equation neglects the influences of potential interactions and cluster internal energy on the condensation process. Here, we present a collision rate theory-molecular dynamics simulation approach to calculate condensation probabilities and condensation rate coefficients. We use this approach to examine atomic condensation onto 6-56-atom Au and Mg clusters. The probability of condensation depends upon the initial relative velocity (v) between atom and cluster and the initial impact parameter (b). In all cases, there is a well-defined region of b-v space where condensation is highly probable, and outside of which the condensation probability drops to zero. For Au clusters with more than 10 atoms, we find that at gas temperatures in the 300-1200 K range, the condensation rate coefficient exceeds the hard-sphere rate coefficient by a factor of 1.5-2.0. Conversely, for Au clusters with 10 or fewer atoms and for 14- and 28-atom Mg clusters, as cluster equilibration temperature increases, the condensation rate coefficient drops to values below the hard-sphere rate coefficient. Calculations also yield the self-dissociation rate coefficient, which is found to vary considerably with gas temperature. Finally, calculations results reveal that grazing (high b) atom-cluster collisions at elevated velocity (>1000 m s) can result in the colliding atom rebounding (bounce) from the cluster surface or binding while another atom dissociates (replacement). The presented method can be applied in developing rate equations to predict material formation and growth rates in vapor phase systems.

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Polycrystalline Bi 0.5 Na 0.5 TiO 3 ͑NBT͒ thin films have been successfully fabricated via a metal organic decomposition process on Pt/ Ti/ SiO 2 / Si substrates. The structural evolution of the as-prepared thin films annealed over the moderate temperature range 500-700°C is studied. NBT thin films annealed at 700°C are of single phase NBT perovskite type. They exhibit a well-defined P-E hysteresis loop at room temperature. The measured dielectric constant is 465-410 over the frequency range of 1 kHz to 1 MHz. The corresponding dielectric loss is ϳ10 −2 . The measured capacitance-voltage curve shows strong non-linear dielectric behavior leading to a high tunability of the dielectric constant, up to 14% at 1 MHz.

8In this study, we explain the causes and effects of the geometrical impossible result 9 encountered in the widely adopted tetrakaidecahedron model (Boomsma and Poulikakos, 2001; 10 Dai et al., 2010)