SEMICLASSICAL AND ENVELOPE-FUNCTION TREATMENT OF MAGNETIC LEVELS IN SUPERLATTICES UNDER AN INPLANE MAGNETIC-FIELD

The theoretical treatment of magnetic levels formed in the minibands of superlattices under an in-plane magnetic field is discussed. It is found that the results of semiclassical and envelope-function treatments based on miniband structures are in good agreement with the results calculated strictly by the quantum-mechanical method, so long as the critical parameter 2hc/eBL2 is larger than 1. The wave functions obtained are in the nature of superlattice envelope functions, which are over and above the usual effective-mass envelope functions for bulk materials.

Post-steam-treatment of Mo/HZSM-5 catalysts: An alternative and effective approach for enhancing their catalytic performances of methane dehydroaromatization

Post-steam-treatment is a facile and effective method for improving the catalytic performances of Mo/HZSM-5 catalysts in methane dehydroaromatization under nonoxidative conditions. The treatment can enhance the stability of the catalyst and also give a higher methane conversion and a higher yield of light aromatics, as well as a decrease in the formation rate of carbonaceous deposits. (27)Al, (29)Si, and (1)H multinuclear magic angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy, and thermogravimetric analysis measurements as well as catalytic reaction evaluations were employed to conduct comparative studies on the properties of the catalysts before and after the post-steam-treatment. The results revealed that the number of free Bronsted acid sites per unit cell decreased, while more Mo species migrated into the HZSM-5 channels for the 6Mo/HZSM-5 catalysts after the post-steam-treatment. In addition, the average pore diameter was also larger for the post-steam-treated catalysts, and this was advantageous for mass transport of the reaction products. However, a severe post-steam-treatment, i.e., with longer treating time, of the 6Mo/HZSM-5 catalyst will lead to the formation of the Al(2)(MoO(4))(3) phases, which is detrimental to the reaction.

Study on the phase behavior of BaEu2Mn2O7 through heat treatment of a single crystal

A new orthorhombic phase of BaEu2Mn2O7 with the space group of Ccmm (no.63) was identified for single crystals after heat treatment and its Crystal Structure was determined by single crystal X-ray diffractometry. The volume Of the unit cell has twice the fundamental tetragonal cell and corner-shared MnO6 octahedra are slightly distorted and Mn-O-Mn angle between the neighboring octahedra tilts with an angle by around 3 degrees from b-axis. It is concluded from the results of the heat treatment of single crystals at various temperatures that this orthorhombic phase changes into a tetragonal One With superstructure (P4(2)/mnm) at 402 K and changes once more into the fundamental tetragonal phase (I4/mmm) above 552 K. The tetragonal phase with superstructure which has been expected to be an unstable one is stable between the two temperatures.