| In recent years, bismuth layer-structured ferroelectrics (BLSFs), such as SrBi4Ti4O15 (SBTi), Bi4-xLaxTi3O12, and SrBi2Ta2O9(SBT) thin films, have been investigated for the applications in high-density capacitors, ferroelectric random access memories, and high temperature piezoelectric devices due to its excellent lower dielectric loss, high Curie temperature, and good fatigue-free properties on Pt electrode. These compounds belong to the Aurivillius family with a general chemical formula of (B2O2)2+(Am-1BmO3m+1)2-, where A is mono-, di-or trivalent elements with dodecahedral coordination, B is a transition cation suited to octahedral, and m is integer which presents the number of perovskite layers, their structure can be regarded as a regular intergrowth of (B2O2)2+layers and (Am-1BmO3m+1)2-pervoskite-like slabs.Among them SrBi4Ti4O15 has high remnant polarization, lower coercive field, and good fatigue-free behavior, but the low Curi Temperature (Tc=520℃) handicaps its practical use. Recently, much attention has been paid on high temperature piezoelectric devices, higher Curie temperature materials are needed for higher temperature application. While CaBi4Ti4O15 has high Curie temperature (Tc=790℃), with the same structure of SBTi. So we did a series of experiments on replacing Sr2+ with Ca2+of SrBi4Ti4O15 film and found that Ca0.4Sr0.6Bi4Ti4O15 (C0.4S0.6BTi) thick film exhibits good ferroelectric properties。The high anisotropic structure of BLSFs results in the ferroelectric properties to be strongly dependent on the crystallographic orientation. The polarization vector of four-layer perovskite BLSFs is only along the a-axis due to the presence of a glide plane and mirror plane along the b and c axes, respectively. To improve the film polarization, it is thus of great interest to design a process that can adjust the crystallization behavior of BLSFs to stimulate the growth of a-axis-oriented crystals. In this paper, (100)-oriented C0.4S0.6BTi thin films were prepared by controlling the heat treatment.C0.4S0.6BTi nanoparticles were prepared by sol-gel method combining self-propagating by varying inflaming time and heat treated process. The microstructure and phase composition of the powders were characterized by XRD and TEM. TEM analysis indicated that the particle sizes of the C0.4S0.6BTi are～60nm. The experimental results showed that single uniform C0.4S0.6BTi nanoparticles were annealed at 800℃for 60 min.The polycrystalline (100)-oriented C0.4S0.6BTi thick films were successfully prepared by powder-gel method on Pt/Ti/SiO2/Si substrates at various conditions. The effects of different pvp addition, sol concentration, spinning speed, pre-annealed temperature and annealed temperature on the crystallization behavior of C0.4S0.6BTi films have been investigated. The phase structure and morphology of films were characterized by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The experimental results showed that the films made by the pvp addition at 0.75%, the sol concentration at 0.15mol/L, the spin coating at 4500r/m, decomposed at 400℃for 3 min and then annealed at 800℃for 5 min preferred a-axis orientation, crack-free and compact, and the crystal of the sample is well grown and has good single-phase.A predominantly (100)-oriented C0.4S0.6BTi thick films were formed on Pt(111)/Ti/SiO2/Si substrates using a powder-gel process combined with a sequential layer annealing method. And then the thick films were annealed in resistance furnace as a function of times ranging from 0 h to 4 h at the annealing temperature. It is found that the films made by annealed at 750℃for 2 h preferred a-axis orientation, crack-free and compact, boll-like grains, with a thickness of about 1.5μm, and the crystal of the sample is well grown and has good single-phase. The film exhibits a well saturated hysteresis loop with a remanent polarization (Pr) of 28.7μC/cm2. Furthermore, the coercive field (Ec) is as low as 126kV/cm. No evident fatigue can be observed after 1010 switching cycles. The values ofεr and tanδat 500 kHz are estimated to be 230 and 0.03, respectively.
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