| Barium stannate(BaSnO3)with an ideal cubic perovskite structure,which behaves as a wide band-gap semiconductor.BaSnO3 not only performs excellent electrical conductivity,transparency,and high-temperature stability,but also is compatible with transition-metal atoms and other types of perovskite materials.After introducing transition-metal atoms into BaSnO3,samples transform from diamagnetism to ferromagnetism.Most of DMSs are synthesized by doping transition-metal elements into conventional semiconductors.Elemental doping leads to tiny lattice distortion in materials,thus modifies the electronic structures of a semiconductor,leading to rich magneto-optic and optical properties.Also internal defects are introduced into materials,such as oxygen vacancies,which commonly exist in DMSs and can't be avoided during the period of material synthesis.Therefore this paper probed the effect of oxygen vacancies on transport properties and magnetic properties of BaSnO3 doping different types of transition-metal atoms through both DFT calculations and experiments.The main research achievements are as following.1.The calculated results of defect formation energy indicated that oxygen vacancies were the most stable internal defect.Based on that,we studied the effect of oxygen vacancies on transport properties of La0.037Ba0.963SnO3 materials.The DFT calculations indicate that in-gap states are introduced into La0.037Ba0.963SnO3 with extra oxygen vacancies.Free electrons mainly originating from the La3+donors are localized around the neighboring O and Sn atoms in the supercell with extra oxygen vacancies being introduced,leading to negative effect on materials' transport properties.2.We probed the effect of oxygen vacancies on ferromagnetism of Ru0.037Ba0.963SnO3 through DFT calculations and experiments.It is experimentally and theoretically demonstrated that increasing oxygen vacancies will greatly depress the ferromagnetic properties.In order to get insight into reasons of the result,we calculated spin-resolved partial density of states(PDOS)of Ru0.037Ba0.963SnO3 with different oxygen-vacancy concentrations.PDOS of spin-up and spin-down states became completely symmetric from obviously asymmetric with the increase of oxygen-vacancy concentrations,which explained the reason that oxygen vacancies have a negative effect on ferromagnetism in Ru0.037Ba0.963SnO3 materials.Our findings can,to some extent,enlighten researchers on the improvement of ferromagnetism by controlling the concentration of oxygen vacancies via optimizing the experimental conditions.3.The magnetism of Mo doped BaSnO3 was investigated in this work from experiments to density functional theory(DFT)calculations.ESR measurements confirm the existence of oxygen vacancies in the samples,and BaMo0.0625Sn0,9375O3-?,where ? represents the number of oxygen vacancies,displays much weaker ferromagnetism compared to the DFT results without spin-orbit coupling(SOC).Therefore,a small orbital contribution restored in spin-orbit coupling(SOC)was introduced for the partial density of states(PDOS)and band structures calculations.The modified DFT calculations indicate that the increase of oxygen vacancies leads to an obvious reduction of the total density of states(DOS)near Fermi level(EF),lower dispersity of conduction band,and deep localized states in the bandgap,which help explain the weak ferromagnetism measured in BaMo0.0625Sn0.9375O3-? containing considerable oxygen vacancies.This study confirms that the contribution of orbital electron states and defects which were ignored in conventional explanation should be considered to solve the elusive magnetism in diluted magnetic oxides,and offers a guide to improve the magnetism. |
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