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The spinel-type LiMn2O4 is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ( F d 3 ÂŻ m ) to tetragonal (I 41/ amd) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn3+/Mn4+ distribution as well as the orientation of the Jahnâ€"Teller elongation of the Mn3+O6 octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn2O4 cathode. [ABSTRACT FROM AUTHOR]

The spinel-type LiMn2O4 is a promising candidate as cathode material for rechargeable Li-ion batteries due to its good thermal stability and safety. Experimentally, it is observed that in this compound there occur the structural phase transitions from cubic ( F d 3 ÂŻ m ) to tetragonal (I 41/ amd) phase at slightly below room temperature. To understand the phase transition mechanism, we compare the Gibbs free energy between cubic phase and tetragonal phase by including the configurational entropy. Our results show that the configurational entropy contributes substantially to the stability of the cubic phase at room temperature due to the disordered Mn3+/Mn4+ distribution as well as the orientation of the Jahnâ€"Teller elongation of the Mn3+O6 octahedron in the the spinel phase. Meanwhile, the phase transition temperature is predicted to be 267.8 K, which is comparable to the experimentally observed temperature. These results serve as a good complement to the experimental study, and are beneficial to the improving of the electrochemical performance of LiMn2O4 cathode. [ABSTRACT FROM AUTHOR]

The analytical potential energy function of HDO is constructed at first using the many-body expansion method. The reaction dynamics of O+HD (v = 0, j = 0) in five product channels are all studied by quasi-classical trajectory (QCT) method. The results show that the long-lived complex compound HDO is the dominant product at low collision energy. With increasing collision energy, O+HD - OH+D and O+HD - OD+H exchange reactions will occur with remarkable characteristics, such as near threshold energies, different reaction probabilities, and different reaction cross sections, implying the isotopic effect between H and D. With further increasing collision energy (e.g., up to 502.08 kJ/mol), O+HD - O+H+D will occur and induce the complete dissociation into single O, H, and D atoms. [ABSTRACT FROM AUTHOR]

Using the different level of methods B3P86, BLYP, B3PW91, HF, QCISD, CASSCF (4,4) and MP2 with the various basis functions 6-311G**, D95, cc-pVTZ and DGDZVP, the calculations of this paper confirm that the ground state is X3B1 with C2v group for CH2. Furthermore, the three kinds of theoretical methods, i.e. B3P86, CCSD(T, MP4) and G2 with the same basis set cc-pVTZ only are used to recalculate the zero-point energy revision which are modified by scaling factor 0.989 for the high level based on the virial theorem, and also with the correction for basis set superposition error. These results are also contrary to X3S[?]g for the ground state of CH2 in reference. Based on the atomic and molecular reaction statics, this paper proves that the decomposition type (1) i.e. CH4 - CH2+H2, is forbidden and the decomposition type (2) i.e. CH4 - CH3+H is allowed for CH4. This is similar to the decomposition of SiH4. [ABSTRACT FROM AUTHOR]

Heteroepitaxial GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy. The growth processes are in-situ monitored by reflection high energy electron diffraction. It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness. This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns. Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm. The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode. The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes. The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films. [ABSTRACT FROM AUTHOR]