| Currently bismuth-based layered ferroelectric material (BLSF) is one of the best candidates for ferroelectric memory. Especially in SrmBi4Tim+3O3m+3(SBTim), represented by Sr2Bi4TisOi8(SBTi5) ferroelectric material, the high remnant polarization, low coercive field strength and leakage current and long holding time makes it become the focus in non-volatile ferroelectric memory material (NVFRAM) studies. But its low Curie temperature limits the use on high temperatures, which make SBTi5 ferroelectric material modification become a hot topic in means of doping substituted, forming solution and symbiotic.In this paper, SBTi5 is taken as the research object, forming solid solution with BiFeO3(BFO) which exhibit multi-ferroelectric property at room temperature and prepared xBFO-(1-x)SBTi (SBFTi-x) composite ceramics. As result we find that with increasing BFO content, Comparing to SBTi ceramic, Bi3+and Fe3+ co-doped in A/B bit not only enhances the lattice distortion degree, also inhibits the Ti4+price change and reducing the Bi element volatile, which reduces the oxygen vacancy concentration, so SBFTi-x ceramic show a high remanent polarization, low leakage current density at room temperature. However, with more BFO components the emergence of structural collapse occur and the improvement of the second phase. In addition, with the improvement BFO content, the changes of oxygen concentration and built-in electric field make the leakage current mechanism of SBFTi-x ceramics turn into the Ohms transmission mechanism-based from the space-charge limit for leading. And SBFTi-x ceramic also show weak ferromagnetism due to the presences of Fe3+.Permittivity of SBFTi-x ceramic is great impacted by the space charge polarization at room temperature, with BFO addition not only increase the dielectric constant also reduce the dielectric loss and ultimately improve the frequency stability. With BFO addition, the Curie temperature continuous increasing and the dielectric peak gradually broadened due to ups and downs of different composition and structure. Besides, the ceramics show diffuse ferroelectric characteristics. The macro resistances of SBTi and SBFTi ceramic have negative temperature coefficient characteristics. The concentration of Fe3+ ion is higher in SBFi-x ceramics at low temperature make its macroscopic resistance decrease gradually, while it weakened at high temperature. SBFTi-x ceramics macro resistance comes mainly from the effect of the grain, and we also find the presence of space charge polarization and mixing relaxation process in SBFTi-x ceramics.AC conductivity of SBFTi-x ceramic is mainly determined by weak bound charge at low temperatures and high frequency, while at high-temperature and low-frequency, AC conductivity is mainly from the rapid increase in the leakage conduction. AC conductivity changes with frequency are closely related to the polarization mechanism. Conductivity mechanism varies with temperature and composition in SBFTi-x ceramics:When the BFO doping amount is from 0.1 to 0.7 the activation energies for conductivity are mainly related to secondary ionization of oxygen vacancies, which is same with SBFTi-0.8 and SBFTi-0.9 ceramics at high temperature (430-480℃) segment. However when it reaches to the low-temperature (250-400℃), conductivity activation energy of SBFTi-0.8 and SBFTi-0.9 ceramics are lower than the conventional ferroelectric material, which may be followed by a high concentration of Fe3+ related.In summary, the composite SBFTi-x solid solution ceramic is formed by inserting BFO into SBTi. We find the high Curie temperature and excellent ferroelectric properties in new composite ceramics, besides we also find weak ferromagnetism and diffuse ferroelectric characteristics, which provide much more possibility for SBFTi-x materials in the field of information storage and magnetic electrical device. |
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