Study On The Phase Structure And Multiferroic Properties Of The Sr-Bi-Mn-O Manganite Composities

In this paper，Bi³⁺ion and Nd³⁺ion are introduced into SrMnO₃by the sol-gelmethod, we got the powder and ceramic of SrxRyMnO₃, achived the purpose thatphase structure of SrMnO₃was changed by substitution of A site ion in the ceramic;the ferroelectric phase Bi₄Ti₃O₁₂was introduced into BiMnO₃, it reduced leakagecurrent and improve the ferroelectric properties and dielectric properties of thematerials effecticly.The powders and ceramics of Manganese oxides of SrBi（Nd）MnO wereprepared by sol-gel with the glacial acetic acid and ethylene glycol; some SrCO₃prepared as impurities, they could be removed by calcination in oxygen-richatmosphere and appropriate nitric acid pickling; in the preparation of BiTiMnO bysol-gel, mixed order of the solution would impact the quality of the sol; utilizationof glycol dissolving manganese acetate can effectively reduce the amount of organicsolvent and drying-time of the gel; the crystal temperature of the crystallization wasat about600oC; by the co-precipitation method with the water bath heating andstirring at100oC for6h, Bi¹²MnO²⁰was synthesized at a lower temperature.Analysis by X-ray photoemission showed that the content of Mn³⁺ions andMn⁴⁺ions closed to the theoretical ratio1:1in the pure tetragonal Sr^0.5Bi^0.5MnO₃,which made leakage current increase; sintering temperature of the SrBiMnO ceramicdecreased with increasing of Bi³⁺content; sintering temperature of SrNdMnOceramic had nothing to do with the content of Nd³⁺, were all about1200oC; coolingin the air makes more ceramics impurity phase, the problem could be sloved byincreasing the holding time.Ceramics of SrBiMnO presented the characteristics of antiferromangnetic withlow saturation polarization around0.2emu/g; ceramics of SrNdMnO system hadweak magnetic, changing of the phase structure induced no ferromagnetic in thematerial; due to high leakage conductivity in the SrBiMnO and SrNdMnO ceramics,dielectric loss increased greatly, dielectric constant anomalisticly increased and noferroelectricity was reflected in two ceramics; each component of BiTiMnO hadweak magnetic, its coercivity was about0.005T （50Gs）, the remanent polarizationwas0.0008emu when the magnetic field intensity was0.2T.The ceramic of BiTiMnO had unusually high dielectric constant, which reached75000¹00000, when the frequency outdistance20kHz, dielectric constant wasbasically the same about15000, dielectric loss was one order of magnitude higherthan the pure dielectric material Bi₄Ti₃O₁₂, it was about1.5; through electric hysteresis line of BiTiMnO, the composition of Bi¹²MnO²⁰has the bestferroelectric properties, indicating that Ti content is not as high as possible, the highTi content caused high sintering temperature, that will introduce impurities andmicro-defects easily.