Browsing by Author "Lu, Feng"
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Item D-Type Anti-Ferromagnetic Ground State in Ca₂Mn₂O₅(IOP Publishing Ltd, 2017-02) Liu, Pan; Wang, Wei-Hua; Wang, Weichao; Cheng, Ya-Hui; Lu, Feng; Liu, Hui; Wang, WeichaoWe study the electronic and magnetic properties of an oxygen-deficient perovskite Ca₂Mn₂O₅ based on the first principle calculations. The calculations show that the ground state of Ca₂Mn₂O₅ is a D-type anti-ferromagnetic structure with the anti-ferromagnetic spin coupling along the c-direction. The corresponding electronic structure of the D-type state is investigated, and the results display that Ca₂Mn₂O₅ is an insulator with an indirect energy gap of ~2.08 eV. By the partial density-of-state analysis, the valence band maximum is mainly contributed to by the O-2p orbitals and the conduction band minimum is contributed to by the O-2p and Mn-3d orbitals. Due to the Coulomb repulsion interaction between electrons, the density of state of Mn-3d is pulled to -6--4.5 eV. .Item Electronic Structure and Ferromagnetism Modulation in Cu/Cu₂O Interface: Impact of Interfacial Cu Vacancy and Its Diffusion(Nature Publishing Group) Li, Hao-Bo; Wang, Weichao; Xie, Xinjian; Cheng, Yahui; Zhang, Zhaofu; Dong, Hong; Zheng, Rongkun; Wang, Wei-Hua; Lu, Feng; Liu, Hui; Wang, WeichaoCu/Cu₂O composite structures have been discovered to show sizable ferromagnetism (FM) with the potential applications in spintronic devices. To date, there is no consensus on the FM origin in Cu/Cu₂O systems. Here, first principles calculations are performed on the interface structure to explore the microscopic mechanism of the FM. It is found that only the Cu vacancy (VCu) adjacent to the outermost Cu₂O layer induces a considerable magnetic moment, mostly contributed by 2p orbitals of the nearest-neighbor oxygen atom (O_(NN)) with two dangling bonds and 3d orbitals of the Cu atoms bonding with the (O_(NN)). Meanwhile, the charge transfer from Cu to Cu₂O creates higher density of states at the Fermi level and subsequently leads to the spontaneous FM. Furthermore, the FM could be modulated by the amount of interfacial VCu, governed by the interfacial Cu diffusion with a moderate energy barrier (~1.2 eV). These findings provide insights into the FM mechanism and tuning the FM via interfacial cation diffusion in the Cu/Cu₂O contact.Item First-Principle Prediction on STM Tip Manipulation of Ti Adatom on Two-Dimensional Monolayer YBr₃(Wiley-Hindawi, 2019-02-04) Liu, Pan; Wu, Maokun; Liu, Hui; Lu, Feng; Wang, Wei-Hua; Cho, Kyeongjae; 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Cho, KyeongjaeScanning tunneling microscopy (STM) is an important tool in surface science on atomic scale characterization and manipulation. In this work, Ti adatom manipulation is theoretically simulated by using a tungsten tip (W-tip) in STM based on first-principle calculations. The results demonstrate the possibility of inserting Ti adatoms into the atomic pores of monolayer YBr₃, which is thermodynamically stable at room temperature. In this process, the energy barriers of vertical and lateral movements of Ti are 0.38eV and 0.64eV, respectively, and the Ti atoms are stably placed within YBr₃ by >1.2eV binding energy. These theoretical predictions provide an insight that it is experimentally promising to manipulate Ti adatom and form artificially designed 2D magnetic materials.Item Investigation of High Oxygen Reduction Reaction Catalytic Performance on Mn-Based Mullite SmMn₂O₅(Royal Soc Chemistry, 2017-10) Liu, Jieyu; Yu, Meng; Wang, Xuewei; Wu, Jie; Wang, Changhong; Zheng, Lijun; Yang, Dachi; Liu, Hui; Yao, Yan; Lu, Feng; Wang, Weichao; 0000-0001-5931-212X (Wang, W); Wang, WeichaoAn alternative material SmMn₂O₅ mullite with regard to Pt/C is proposed to catalyze the oxygen reduction reaction (ORR) by combining density functional theory (DFT) calculations and experimental validations. Theoretical calculations are performed to investigate the bulk phase diagram, as well as the stability and electrocatalytic activity of the ORR under alkaline conditions for SmMn₂O₅ (001) surfaces, which are passivated by nitrogen atoms to avoid any spurious interference. The adsorptions of relevant ORR species (O*, OH*, OOH* and OO*) tend to compensate the coordination of manganese atoms to form Mn-centered octahedral or pyramidal crystal fields, and the corresponding binding energies fulfill a linear relationship. An oxygen molecule prefers to be reduced to OH⁻ via a four-electron pathway and this prediction is verified by electrochemical measurements on the as-prepared SmMn₂O₅ catalyst with a nanorod structure. Volcano curves are obtained to describe the trends in theoretical ORR activity as a function of a single parameter, i.e. the oxygen binding energy. An overpotential of 0.43 V is obtained at the O* binding energy around 3.4 eV, which is close to the experimental observation (0.413 V) in this work. SmMn₂O₅ mullite exhibits favorable ORR activity and superior stability with only ~5% decay in activity over 20 000 s of chronoamperometric operation in contrast to ~15% decrease of Pt/C, making it a promising candidate for a cathode catalyst.