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Lanthanum silicates La10Si6−xMgxO27−x (x = 0–0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La10Si6−xMgxO27−x (x = 0–0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La10Si6O27, and La10Si5.8Mg0.2O26.8 exhibits the highest conductivity with a value of 3.0×10−2 S ·cm−1 at 700 °C. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper. [ABSTRACT FROM AUTHOR]

We study the nucleation mechanism and morphology evolution of MoS2 flakes grown by chemical vapor deposition (CVD) on SiO2/Si substrates with using S and MoO3 powders. The MoS2 flake is of monolayer with triangular nucleation, which might arise from the initial MoO3−x that is deposited on the substrate, and then bonded with S to form MoS2 flake. The ratio of Mo and S is higher than 1:2 at the beginning with Mo terminated triangular nucleation formed. After that, the morphology of MoS2 flake evolves from triangle to similar hexagon, then to truncated triangle which is determined by the faster growth speed of Mo termination than that of S termination under the S rich environment. The nucleation density does not increase linearly with the increase of reactant concentration, which could be explained by the two-dimensional nucleation theory. [ABSTRACT FROM AUTHOR]