| BiFeO3 (BFO), as a lead-free multiferroic material, has aroused great interest due to its simultaneous exhibition of ferroelectricity and antiferromagnetism at room temperature. Superior ferroelectric properties with the remanent polarizations (Pr) of about 100μC/cm2 have been observed in polycrystalline and epitaxial BFO films deposited using pulsed-laser deposition, sputtering and metal organic chemical vapor deposition. For the BFO films prepared using metal organic decomposition (MOD), it is difficult to observe the saturated polarization-electric field (P-E) hysteresis loops with the Pr values above 60μC/cm2. This should be due to that the MOD derived BFO films have the higher leakage current densities and the larger coercive fields. Therefore, how to control leakage current and lower coercive field are the critical factors to enhance the ferroelectric properties of the BFO films and for the applications of BFO in devices. Recently, ion substitutions, including Bi-site doping with lanthanide and substitution Fe ions by transition metal cation, has been verified to be an effective method not only in improving the leakage characteristics but also in lowering the coercive field, to some extent, of BFO films. In this paper, we investigate systemically the relationships between preparation processing, defects, structures and properties of the BFO films doped with Mn and Pr deposited on indium tin oxide bottom electrodes using MOD technique.The research work and major conclusions are as follows:1, We study the influence of Mn substitution on the structures and electric properties of BFO films. The experiment results demonstrate that: (1) As the increasing of Mn doping content, the relative intensities of (012) peaks increase gradually and the positions of (024) peaks shifts to the high angles of 2θ. (2) The growth of grain in BFO films are limited by Mn substitution. (3) The leakages of Mn-doped BFO (BFMO) films are increasing with the increase of Mn content. (4) Compared to the content of Fe2+ in BFO, Mn substitution can suppress the generation of Fe2+. (5) The 5% Mn-doped BFO film has the outstanding ferroelectric properties with a remanent polarization of 75±3μC/cm2. (6) The spontaneous polarization directions of BFMO with the Mn doping content lower than 7% still close to the body diagonals of the unit cell, although the phases of BFMO transit from rhombohedral to tetragonal induced by Mn substitution.2, We investigate the effects of annealing method (i.e., the sequential-layer annealing process and the conventional annealing process) on the electric properties of 5% Mn-doped BFO films. We find that: (1) Compared to the film annealing using the conventional method, the sequential-layer annealed film shows more compact structure. (2) In comparison with the film annealing using the conventional method, the sequential-layer annealed BiFe0.95Mn0.05O3 film has the larger Pr value and more asymmetric coercivity. (3) The asymmetry in coercive of BFMO films should be originated from the preferential orientation of ferroelectric domains (as a result of stresses in the films) and deteriorated by the aging during annealing treatments.3, The influences of Pr doping (the doping content ranges from 10% to 20%) on the ferroelectric and dielectric properties of BiFe0.95Mn0.05O3 films are studied systemically. The findings of these experiments are as follows: (1) The largest Pr value and dielectric constant can be observed in the 14% Pr-doped BiFe0.95Mn0.05O3 film. (2) These ferroelectric thin films exhibit the typical traits of double P-E hysteresis loops when the Pr doping content higher than 16%. (3) The morphotropic phase boundary may present in the film with Pr content of 14±1% owing to the distortion of lattice induced by the substitution of Bi by Pr.
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