Investigations On Electronic Structure Of ABO₃ Multiferrous Materials By Electron Energy Loss Spectroscopy

Multiferroic materials have attracted increasing attention due to the rich physical properties.In this paper,the electronic structure characteristics of several multiferroic materials are studied by using density functional theory and electron energy loss spectroscopy.The main research contents are as follows:The relationship between electronic structure and basic physical properties of YMnO₃ system was studied.The calculated atomic density of states is used to analyze the low energy part of the electron energy loss spectrum,and distinguish the loss peaks caused by plasma oscillation or single electron transition.The ferroelectric origin of YMnO₃ is related to the hybridization between O 2p and Mn 3d,Y 4d.The formation of O-Mn and O-Y covalent bonds play a stable role in ferroelectric properties.The ferromagnetism of YMnO₃ is mainly related to the spin asymmetry of Mn 3d orbital electron states.The formation reasons of energy loss near edge structure(O K edge and Mn L_2,3 edge)are explained by the density of vacancy states above the Fermi surface,and Mn L_2,3 edge of different valence states are simulated,revealing that Mn mainly exists in the trivalent state in YMnO₃.Electronic structure and multiferroic properties of Fe atom doped In MnO₃ were studied.The covalent bond of Mn-O and In-O can promote the formation of ferroelectric phase in In MnO₃,and the hybridization between Mn 3d state and O 2p state can also promote the formation of ferroelectric phase.According to the analysis of energy band structure and density of state,In MnO₃ shows no magnetism,and the total magnetic moment of the system is verified to be zero by Mulliken population.In order to research the effect of Fe atom on the system,In12Mn10Fe2O36 is taken as the research object.It is found that Mn provided magnetic moment and Fe also has spin asymmetry.The relationship between electronic structure and macroscopic physical properties of Bi FeO₃ was studied.According to the energy band structure,the direct band gap value of Bi FeO₃ is 1.722 e V,indicating that it has semiconductor properties.The ferroelectric mechanism of Bi FeO₃ is mainly related to the lone pair electrons in the Bi 6s orbit hybridized with O 2p orbital electrons.The main peak of low energy loss spectrum is the plasma loss peak produced by valence electron collective oscillation,the other characteristic peaks are due to the single electrons excitation from the valence band to the conduction band.Experimental and theoretical results show that the core hole effect plays an important role in the simulation.The electronic structure of Bi FeO₃ doped with different cations were studied.The Bi₁₂Fe₁₂O₃₆ supercells are doped with ions at the same concentration and different positions,such as Ca ion at A position,Mn ion at B position,Gd and Co at A/B position.Ca ion in Bi₁₁CaFe₁₂O₃₆ supercell restrains the magnetism of Fe atoms in the original structure,making Fe atoms appear three forms of density of state.In Bi₁₂Fe₁₁MnO₃₆ system,the magnetic moment provided by Mn ion is 2.07?B,but it restrains the spin polarization of some Fe atoms.In the Bi11 Gd Fe11CoO₃₆ system,the doping of Gd and Co restrains the spin polarization of Fe atoms,and Co provides a small amount of magnetic moment,the magnetic moment of overall system is mainly provided by Gd ions.