Structure And Multiferroic Properties Of Transition Metal B-site Doped Barium Niobate

Perovskite(ABO3)niobates are widely used in photocatalysis,optoelectronic devices and biological medicine due to its excellent physical properties,which endowed by its unique oxygen octahedral structure.As one of the rare two valences A-site cation materials in perovskite niobates,BaNbO3 is less reported,especially the research on its elements doping modification.Thus,it is necessary to carry out the researches on the crystal structures and intrinsic physical properties of BaNbO3 and its doped counterparts.In this paper,density function theory was introduced in material calculation,combining the methods of first-principal calculation and experimental verification,the electronic structures and intrinsic physical properties of BaNbO3 crystal and B site doped BaNb(1-y)XyO3(X = Fe,Co,Ni,Cu,Zn)crystals were investigated systematically.Calculation results showed mechanical stability of BaNb O3 was poor and magnetic was weak,while spontaneous polarization appeared.B-site doping of transition metal enhanced the lattice stability and magnetic.The BaNbO3 and BaNb(1-y)XyO3(X = Fe?Co?Ni?Cu?Zn)crystal were synthesized by composite hydroxide mediated method(CHM).XRD,XPS and SEM were used to study its structure and morphology.UVs,VSM and ferroelectric measurement were taken use to analyse their band gap and multiferroic properties.On the basis of calculation result,the effects and mechanisms of doping to their electric and magnetic properties were studied.First principle calculation results showed that BaNbO3 crystal is a direct band gap semiconductor,with the band gap of 2.60 eV.The top of the valence band was contributed by O 2p orbit and the bottom of the conduction band is mainly composed of Nb 4d and O 2p orbits.BaNb O3 crystal showed Pauli paramagnetic.Nb-O was ionic bond,while Ba-O was antibond.Electrons transfer of Ba was not obvious,which means that Ba atoms were weak bound to oxygen octahedron.BaNb(1-y)XyO3(X = Fe,Co,Ni,Cu,Zn)crystal models were built.Calculated results indicated a decrease of bandgap with X doping.Simulated XRD indicated that their lattice constants decrease and peaks split with cell distortion.Fe/Co/Ni-doped BaNb(1-y)XyO3 were magnetic,which are contributed by the non-fully filled 3d orbit of dopant atoms and Nb 4d orbit.However,Cu/Zn-doped one did not show magnetic.Ba,Nb,(Fe,Co,Ni,Cu,Zn)lost electrons,and O was acceptor.Transition metal B-site replacement increased NbO covalency.Mulliken Population showed that Fe-O,Co-O,Ni-O,Cu-O bonds were more covalent than Nb-O bond and Zn-O bond was antibond.BaNb O3 was prepared by composite hydroxide mediated method(CHM).Well dispersed cube BaNbO3 crystals with edge size of 200 nm were obtained by using the BaCl2·2H2O and Nb2O5 as the barium and niobium source,under the reaction conditions of temperature at 195 oC,24 h and 1:1 reaction molar ratio.BaNb(1-y)XyO3(X = Fe,Co,Ni,Cu,Zn)crystals were successfully synthesized by the same method.XRD results showed that the diffraction peaks of BaNb(1-y)NiyO3 sample showed obvious redshift,Besides,the experimental lattice constants were larger than the calculated results.The SEM images showed that BaNb(1-y)FeyO3 crystal have bigger size,approaching to 600 nm,and other elements doped BaNb(1-y)XyO3(Co,Ni,Cu,Zn)crystals were about 100-250 nm.UVs-vis showed that the band gap of BaNbO3 crystal was 4.20 eV,which was bigger than the calculated result.BaNb(1-y)FeyO3 crystal has broadband absorption ranged from ultraviolet to visible light,with band gap of 2.97 eV.Comparing with pure BaNbO3 crystal,the band gap of BaNb(1-y)NiyO3 crystal deceased by 0.21 eV,while BaNb(1-y)CoyO3 crystal kept unchanged,however,a small peak appeared around 440 nm in Co-doped one.And the band gap of BaNb(1-y)(Cu,Zn)yO3 crystals almost keep unchanged.BaNbO3 was ferroelectric,while BaNb(1-y)XyO3(Co,Ni,Cu,Zn)was non-ferroelectric.Magnetism test results indicated that Ba NbO3 and BaNb(1-y)(Cu,Zn)yO3 were Pauli paramagnetic,while Fe/Co/Ni-doped materials showed obvious ferromagnetic behavior.Their ferromagnetic properties can be attributed to the hybridization of non-fully occupied d orbits of doped elements with O 2p orbits.