The spin-polarized generalized gradient approximation(GGA)+U approach was employed to study the bonding characteristics and magnetic coupling interactions in room-temperature phase α′-NaV2O5. The calculated results indicate that the Vdxy orbital is split off from other 3d orbitals in the VO5 pyramidal ligand field. The Vdxy orbitals are hybridized strongly with the Opx/py orbitals, forming a V―O―V π bond in the ab plane. The ligand field effect together with the intra-atomic exchange splitting results in the insulating behavior. With the aid of Noodleman's broken symmetry methods, the magnetic exchange constant was derived from mapping the relative energies onto the Heisenberg model. The antiferromagnetic(AFM) exchange energy, J, along the chain was calculated to be -593 K in good agreement with the experimental data.
FAN Hou-gangMING XingHU FangWANG Chun-zhongHUANG Zu-feiCHEN Gang
Monoclinic Li0.5MnO2 was synthesized by solid state reaction and the spectral and magnetic properties were studied in comparison with those of spinel LiMn2O4.The XRD pattern and Raman spectrum of Li0.5MnO2 are different from those of LiMn2O4,which indicate the different long-range and short-range crystal structure.XPS result shows the binding energies of 2p3/2 and 2p1/2 in Li0.5MnO2 are located at 642.3 and 653.6 eV,respectively.Through fitting the XPS spectra,the valence state of Mn ion in Li0.5MnO2 coincides with that in LiMn2O4.The high-temperature susceptibility of Li0.5MnO2 can be fitted by Curie-Weiss law whose Curie and Weiss constants are 33 A·m2·K/(mol·T) and-277(6) K,respectively.Although Li0.5MnO2 shows spin glass ground state,the transition temperature of Li0.5MnO2 is about 9 K lower than that of LiMn2O4.
WANG Deng-panl, CHEN Hong1＇2, DU Fei3＇4, BIE Xiao-feil, LIU Li-nal, WEI Ying-jin3, CHEN Gang3＇4 and WANG Chun-zhong3.CHEN HongDU FeiBIE Xiao-feiLIU Li-naWEI Ying-jinCHEN GangWANG Chun-zhong
α'-NaV2O5 was prepared by a simple hydrothermal process.X-ray diffraction confirmed the orthorhombic structure of α'-NaV2O5,with preferential growth along the (001) direction.Scanning electron microscopy showed α'-NaV2O5 was composed of flake-shaped crystals.X-ray photoelectron spectroscopy confirmed the co-existence of V4+ and V5+ in α'-NaV2O5,which results in an average V4.5+ oxidation state of α'-NaV2O5.The observed Raman bands are ascribed to different V―O vibrations.α'-NaV2O5 shows a reversible specific capacity of about 100 mA·h·g-1 between 3.5 and 1.0 V,with a good capacity retention.The good electrochemical stability of the material is attributed to its structural stability during Li+ intercalation.
HU Fang WEI Ying-jin JIANG Tao MING Xing CHEN Gang WANG Chun-zhong
