Composition Design And Properties Improvement Of Bismuth Layer-structured Ferroelectrics Materials

Due to the excellent endurance properties against polarization switching, low coercive field and fast switching time, bismuth layer-structured ferroelectrics (BLSFs) have great potential in ferroelectric random access memories. Meanwhile, BLSFs with properties such as high Curie temperature, anisotropy property for Kt, low aging rate, high resistivity and great quality for dielectric breakdown, are have attractive proper to apply as pizeoelectric at high temperature and high frequency conditions. However, different layered BLSFs have shortcoming limited their applicatuon, thus, it is important to study the dielectric and ferroelectric properties induced by crystal structure. As the materials have relative inferior piezoelectric properties, ion doping was used to improve the properties which are a guidence for their application as piezoelectric devices.Pb1-xSrxBi2Nb2O9 (0≤x≤0.2) and Pb0.8Ba0.2Bi2Nb2O9 ceramics have been prepared by coventional solid state methods. The size of grain becomes smaller with the increasing amount of Sr2+. Sintering temperature of samples has decreased for 80℃by Sr2+ doping. The value of the relaxation parameterγis above 1 estimated from the linear fit of the modified Curie-Weiss law with other empirical parameters (?Tm, ?Trelax) indicate the relaxor nature for PBN-Ba0.2. Ba2+ may occupy the Bi site in the Bi2O2 layers and the disorder of Ba2+ and Bi3+ in the Bi2O2 layers should be a probable source of the dielectric relaxor behavior for PBN-Ba0.2. The d33 value increased to 11 pC/N for PBN-Ba0.2. Well-developed P-E hysteresis loops are obtained from PBN-Ba0.2. The Pr values were improved to 10.5μC/cm2 at 423K when Ba2+ introduce into PBN-based ceramic.Bax(Na_0.5Bi_0.5)1-xBi4Ti4O15 (0.04≤x≤0.1) soild solution, belong to the nomal ferroelectic, was obtained. SEM shows samples high density for grains without pores. The Tc can adjust by the introduction of Ba2+. Theεand tanδhas litter relation with frequence in 1 kHz¹00 kHz. The d33 value was improved to 14 pC/N at room temperture for Ba0.1(Na_0.5Bi_0.5)0.9Bi4Ti4O15.A_m-3Bi₄Ti_mO_3m+3 (A=Ca, Ba; m=3, 4, 5) were successfully prepared, while the efforts to synthesize Ba3Bi4Ti6O21 resulted in a mixture of Ba2Bi4Ti5O18 and BaTiO3, respectively. Bismuth layer structure, occupied 81.97% of the phase, is the main compound as calculate from XRD data. One reason for this phenomenon is the large radii in A-Site for Ba3Bi4Ti6O21. The dielectric diffusion in BaBi4Ti4O15 and Ba2Bi4Ti5O18 were explained using the random-field theory. With increasing of m from 3 to 5, the Tc decreased, while the remanent polarization is dependend on the even or odd for m. Cam-3Bi4TimO3m+3 (m=4, 5, 6) were proved to be ferroelectric. No dielectric constant anomaly was found in the range from room temperature to 650℃for Cam-3Bi4TimO3m+3 (m=4, 5, 6) ceramics, so their Tc are higher than 650℃.