Preparation And Properties Of Multi - Ferrous BiFeO 3 Materials

The BiFeO3 nanopowders were successfully synthesized by a chemical precipitation method. The fabrication of BiFeO3 ceramics by conventional pressureless sintering and spark plasma sintering were also investigated. The influence of key factors on synthesis of BiFeO3 nanopowders, and the influence of sintering technique on the microstruture and phase of BiFeO3 ceramics, as well as the relationship between which and their dielectric, ferroelectric, magnetic properties were studied systematically by means of XRD, LPS,XPS, SEM, etc.The results show that the better pH of Fe3+-Bi3+-NO3--NaOH-H2O co-precipitation system is 11.0, and the calcination temperature, preservation time and Bi elements in excess are ultimately determined at 550 ℃,1.5h and 3% which are the ideal conditions for powder synthesis.When the co-precipitation reaction time is 95h, the precursor powders calcined at 550 ℃ for 1.5h have fine and uniform particle size distribution and are of pure BiFeOs phase with the average particle size of about 60 nm. The BiFeO3 ceramics with pure phase were obtained by Spark Plasma Sintering. The relative density of BiFeO3 ceramics reach up to 98.3% and ceramic grain size is between 1 to 2 μm.The conventional pressureless sintering ceramics sintering at 825 ℃ are dense with relative density of 91.6%, and generate the impurity phase; Ceramics shows poor dielectric properties, at the frequency of 30MHz, the dielectric constant is 21.6, dielectric loss is 0.203.Through comparing conventional pressureless sintering samples with spark plasma sintering samples, Bi ions evaporation is reduced by spark plasma sintering through fast heating rate, no Fe2+ generate, the oxygen vacancy reduction compared to the traditional sintering method, improve the resistivity of ceramic samples.With the increase of temperature, the grain size of spark plasma sintering BiFeO3 ceramics increase; At 600 ℃ and 650 ℃, BiFeO3 ceramics with pure phase is obtained and BiFeO3 grains are equiaxed. Ceramics sintered 600 ℃,650 ℃ and 700 ℃ are all dense and the relative densities of ceramics sintered 600 ℃ and 650 ℃ has reached more than 98%. When the frequency is 30MHz, the dielectric constants of ceramics sintered 600℃ and 650℃ are 115.4 and 106.5 respectively, dielectric loss of ceramics sintered 600℃ and 650℃ are 0.006,0.006 respectively. Saturated hysteresis loops are observed in ceramics sintered 600℃, saturation polarization Ps, the remaining polarization Pr and coercive field strength Ec are 0.4μC/cm2,0.14 μC/cm2 and 2690V at 8kV voltage.