Preparation And Magnetic Studies Of Pervoskite BaNbO₃Nanomaterial With Transition Metal （Fe, Co, Ni） Doping

In recent years, the pervoskite niobates have received much scientific attentionbecause of their great potential in ferroelctric, dielectric, piezoelectric, and nonlinearoptical applications. With the rapid development of the new materials andnanotechnology, it is found that pervoskite niobates based materials have been widelyapplied in electron industry, photocatalyts, ceramics, and aviation industry, etc. So theresearch of synthesis, property and application of pervoskite niobates based nanomaterials is an urgent and interesting work.In this paper, we tried to develop a novel simple method to prepare BaNbO₃andtransition metal ions-doped BaNbO₃using the composite-hydroxide-mediated （CHM）method, which is a new strategy that has advantages of a low temperature andatmospheric pressure, one-step, convenient, low-cost, nontoxic and easy to scale up.The samples were characterized by X-ray diffraction （XRD）, Energy Dispersive X-RaySpectroscopy （EDS）, Field emission Scanning Electron Microscope （SEM）. They showthat all of the samples are pervoskite niobates with a typical cubic shape. The averagesize of BaNbO₃and Fe/Co/Ni-doped BaNbO₃is300-500nm,100-300nm, respectively.From the XPS, we know that Fe³⁺，Co²⁺，Ni²⁺replaced the Nb⁴⁺in BaNbO₃lattice.Since radius of Nb⁴⁺is74pm, which is larger than that of64pm (Fe³⁺),72pm (Co²⁺),59pm (Ni²⁺), the XRD peaks of Fe/Co/Ni-doped BaNbO₃shift a little toward largeangle compared with pure BaNbO₃due to the lattice space shrinkage from the smallersize ion replacement.At the same time, we studied the changes in magnetic between BaNbO₃andtransition metal ion doped BaNbO₃. From the magnetic hysteresis cures, the samplesshowed obvious ferromagnetic property after doping. Through the zero field cooling（ZFC） test by Physical Property Measurement System （PPMS）, we eliminate thepossibility of ferromagnetic behavior which comes from the Fe/Co oxide impurities inthe powders. In order to discussion and analysis the reason why the samples showmagnetic after doping, we calculate them with first principles calculation. As a bariumniobate belongs to the structure of perovskite （ABO₃）, in which six oxygen form oxygenoctahedrons, and niobium is located in the center of the oxygen octahedrons, andbarium is in octahedral gap, the calculation is based on40atoms model （8Ba atoms,8Nb atoms,24O atoms）. From the calculation results, we found that the fermi level have changed its position after doping and exhibited half-metallic behavior in which thespin-down shows metalline and the spin-up shows semiconducting character.Ferromagnetic property originates from the splitting of Fe/Co d states in BaNbO₃crystal.