| Bismuth Layer-Structured Ferro electrics (BLSFs) are widely studied because of their good ferroelectric properties and environmentally friendly character. Generally, the formula of BLSFs is (Bi2O2)2+(Am-1BmO3m+1)2-, where B and A are metallic ions, and m is the number of BO6octahedra in the perovskite blocks. The perovskite blocks (Am-1BmO2m+1)2-are sandwiched between bismuth oxide layers (Bi2O2)2+along the c-axis. Compared with bismuth layer-structured ferroelectric materials, multi-ferroelectric material BiFeO3(hereinafter referred to as BFO) is triangle distorted perovskite structure, formatted from cubic structure tensile along the [111] direction, Due to lack of central symmetry and larger interatomic relative displacement, BFO has higher spontaneous polarization theoretically, and shows great development prospect as well as BLSFs.Though the compositions and structures of BLSFs and BFO are different, their ferroelectric properties always depend on the oriented growth of material grains. In this paper, the preparation of the precursor, spin-coating and annealing processing of the film prepared by Sol-Gel method was discussed. The grain orientation of films was achieved by optimization of process parameters. It is the preferred orientation of the film that can improve its ferroelectric property. In addition, templated grain growth (TGG) is also a kind of method to optimize orientation growth of the solid material grains. In detail, oriented grains were used to induce the growth of desultorily ceramic. The ordered arrangement of the ceramic grains, i.e., textured growth can improve its ferroelectric properties enormously. So, soluble NaCl crystal was used as substrate. Oriented ferroelectric thin films (obtained by dissolving the soluble substrate) were used as templates to induce the bulk textured, and then the properties of BLSFs and BFO were improved at the same time.First, the NaCl substrates were characterized and analyzed. According to the XRD result, NaCl substrate shows (100) orientation and good crystal quality, which is beneficial to the epitaxial growth of films. SEM micrograph shows that the surface of NaCl substrate was even and neat enough to facilitate the uniform coating of films. Combined with the physical properties of CSBT and BFO, the lattice mismatch between films and substrate was3.91%and0.178%, which belongs to complete matching interface. The coefficient of thermal expansion of both film and substrate is in the same order of magnitude, from which the stress results is also small enough. It can be seen that it is feasible for the deposition of ferroelectric films on NaCl substrate.Second,(100) oriented uniform and continuous CSBT films were deposited on NaCl substrates. And the effect of uniform coating speed, pyrolysis temperature, annealing temperature and annealing time on the phase structure, micro structure and internal stress of CSBT films were discussed. Then the best technique for oriented CSBT films can be summarized as follows:uniform coating speed of2500r/min, pyrolysis temperature of350℃, annealing temperature of700℃, and annealing time for300s. According to AFM characterization, the CSBT film prepared at best condition showed spherical grain, whose diameter is about100nm, and roughness is about1.75nm. By the SEM observation on the cross section of CSBT film, its thickness was measured about175μm.Third, the inducement of CSBT film was studied. Oriented CSBT films were pressed into ceramic powder. And experimental result shows that after the induction of CSBT templated film, CSBT ceramic bulk shows prefer (100) orientation, lower full width at half maximum (FWHM), and better crystallization quality, indicating the success induction of templated CSBT films.Fourth, the preparation technology of BFO film on NaCl substrate was discussed. BFO film was deposited on NaCl substrate because of its low crystallization temperature. Based on the DSC analysis results, BFO films were prepared on NaCl substrate. In order to obtain (100) oriented BFO film, the effect of solution concentration, uniform coating speed and annealing temperature on phase structure of BFO films was studied. The best preparation technique is solution concentration of0.3mol/L, uniform coating speed of4000r/min, and annealing temperature of400℃. SEM results showed that the surface of BFO film deposited at optimum technological condition was smooth and crackless, and most of the grains were spherical grains, about40nm in diameter averagely and80microns in thickness. The preparation of oriented BFO film is promoting to the study of textured BFO bulk material... |
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