| Recently, (Ba,Ca)TiO3 related materials have received the increasing interests because of the unique dielectric, ferroelectric, and piezoelectric Properties. In the Present work, the Preparation, structure and properties have been investigated systematically for (Ba,Ca)TiO3 related ceramics and thin films, and the following conclusions have been obtained.The (Ba,Ca)TiO3 ceramics show a broaden tetragonal phase region, the enhanced polarization, improved dielectric strength, and suppressed dielectric loss. The EELS-STEM analysis gives the direct evidence of Ca occupance at Ti-site. The analysis of high angle annular dark field-scanning transmission electron microscopy (HADDF-STEM) and annular bright field-scanning transmission electron microscopy (ABF-STEM) show that the Ti ions move to the same direction with oxygen octahedral, which is different with that in BaTiO3, and similar to the situation in PbTiO3. The big increase of the displacement of oxygen and Ti ions is the origin of the enhancement of polarization in (Ba,Ca)TiO3.The solid solutions can be formed between (Ba0.75Ca0.25)TiO3 and BiFeO3, and there is a rhombohedral and tetragonal two phase copresence region, which could improve the ferroelectric, piezoelectric and ferromagnetic properties of the multiferroic BiFeO3. At room temperature, the optimized composition Bi0.7(Ba0.75Ca0.25)0.3Fe0.7Ti0.3O3 shows a ferroelectric polarization (Pr～43 μC/cm2), remnant magnetization (0.07 emu/g,300 K), and large strain (～0.2%). The comprehensive enhancement of ferroelectricity, piezoelectricity, and magnetization in (Ba0.75Ca0.25)TiO3-BiFeO3 suggests that introducing phase boundary is a promoting way of the modification of BiFeO3 multiferroic ceramics.Multilayered (Ba,Ca)TiO3-Ba(Zr,Ti)O3 thin fims have been successfully prepared by pulsed laser deposition on (001) Nb:SrTiO3 substrate. By adjusting the number of layers, the interface effect on domain structure and the piezoelectric signal have been investigated. XRD and TEM analysis reveals the sharp interfaces and epitaxial nature at the BCT/Nb:STO interface, and multi-oriented twin domain structures forms near the surface as the number of layers increases. All films exhibits an intense polarization component in out-of-plane phase, and inferior in-plane phase contrast. As periodic number (N) increases, the out-of-plane phase contrast increases greatly and better switching behaviors are observed. The N = 8 film shows the best domain structure and saturated local piezoelectric response loop. The result indicates that the interface and twinning structures play an important role in improving the piezoelectric response increases.Highly oriented triple layered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films have been successfully prepared on (001) Nb:SrTiO3 substrates by pulsed laser deposition. The multilayers consist of three distinct layers with designed thickness combination of 1:1:1 and 2:1:1 with total thickness ～300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The samples with 2:1:1 configuration show higher in plane piezo response, smaller coercive field. The optimized combination was found to be the BaTiO3-(Ba0.85Ca0.15)TiO3-CaTiO3 structure with combination ratio 2:1:1, which displays the best switching behavior, room temperature dielectric constant ～ 700, dielectric loss of 0.03, and large dielectric tunability of～50% at 400 kV/cm. This result suggests that the enhanced dielectric and tunability performance is greatly associated with the large in-plane polarization component. |
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