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Doping and constructing intergrowth are found to be an effectual approach to modify the electrical properties of bismuth layer-structured ferroelectrics. In this work, ferroelectric, piezoelectric and dielectric properties of Nb-doped Bi4Ti3O12-SrBi4Ti4O15 (BTN-SBTN-x) intergrowth ceramics were investigated. The ferroelectric property of Bi4Ti3O12-SrBi4Ti4O15 was improved by niobium doping. The remanent polarization (2P r ) increases at first, then decreases with the increase of niobium content, while the coercive field changes little with Nb-doping. As niobium content is 0.06, the 2P r maximizes at a value of 34.9 μC/cm2, which is increased by about 75% in comparison with that of Bi4Ti3O12-SrBi4Ti4O15 (2P r = 20.0 μC/cm2). The Curie temperature of the samples varies hardly upon Nb-doping, which indicates that the good thermal stability of Bi4Ti3O12-SrBi4Ti4O15 is not deteriorated after Nb addition. Piezoelectric coefficient d33 was increased from 9.3 pC·N−1 to 18.6 pC·N−1 due to the enlargement ...

La-doped SrBi4Ti4O15, SrBi4–x La x Ti4O15 (SBLT-x, x = 0.00, 0.10 and 0.25), thin films have been successfully prepared by the sol–gel method. Structures, surface morphology and ferroelectric properties were investigated. Compared with undoped SBTi, SBLT-0.10 shows a notable larger remnant polarization (2P r = 46 μC/cm2). Meanwhile, the SBLT-0.10 film shows little change of P nv and −P nv up to 4.4 × 1010 switching cycles, suggesting an excellent fatigue-endurance characteristics.

Ferroelectric ceramics of lanthanum-modified SrBi4Ti4O15 and Bi4Ti3O12-SrBi4Ti4O15 have been synthesized, and Raman spectrum measurements have been carried out at room temperature. The investigation on the Raman spectra suggest that La3+ ions prefer to occupy the A site in the case of x ≤ 0.10, and at higher content they tend to be incorporated into Bi2O2 layers in the La-doped SrBi4Ti4O15. As for La-doped Bi4Ti3O12-SrBi4Ti4O15, the critical content of the doping ions is 0.50. An interesting phenomenon has been noticed that the remnant polarization maximized at about the critical doping content. Thus, it can be concluded that the Bi2O2 layers have a very important effect on the properties in the bismuth layer-structured ferroelectric materials.

Sr2Bi4Ti5O18 (SBTi) and Sr-deficient SBTi thin films were deposited on Pt/Ti/SiO2/Si(100) substrates using a sol-gel method. Structure, morphology and electric properties were investigated systematically. These films were random-oriented and were composed of rod-like grains. The remanent polarization (2P r ) and coercive field (Ec) of SBTi films were 24 μC/cm2 and 68 kV/cm, respectively. This value of 2P r was much higher than the reported value of SBTi prepared by pulse laser deposition. The compounds with Sr-deficient and Bi-excess composition showed a very large remanent polarization of 35.5 μC/cm2. More importantly, both films showed high fatigue resistance against continuous switching up to 3 × 1010 cycles and excellent charge-retaining ability up to 3 × 104 s.

An investigation on the ferroelectric and dielectric properties of higher-valent-cations Nb-and Mo-modificated SrBi4Ti4O15 ceramics was presented. The ferroelectric property of SrBi4Ti4O15 was both obviously improved by niobium and molybdenum doping. The remnant polarization (2P r ) of both Nb-and Mo-modificated SrBi4Ti4O15 increases at first, then decreases with further doping. As the doping content is 0.03 and 0.06 respectively, the 2P r maximizes at a value of 24.7 μC/cm2 and 26.5 μC/cm2, which is about twice larger than that of SrBi4Ti4O15. Meanwhile, the coercive field is increased less than 20% upon Nb and Mo substitution. The Curie temperature of the samples shifted hardly by Nb-and Mo-doping, which indicates that the good thermal stability of SrBi4Ti4O15 is not affected.

La, Nd, Sm, and Dy-doped Sr{sub 2}Bi{sub 4}Ti{sub 5}O{sub 18} (SBTi) ceramic samples have been prepared by the solid-state reaction method. The X-ray diffraction reveals that all of the ceramic samples are single phase compounds. Their remnant polarization (2P {sub r}) increases at first, and then decreases with the increase of doping content. When doping content is 0.01, Sm and Dy-doped SBTi samples exhibit the maximum 2P {sub r} of 18.2 and 20.1 {mu}C/cm{sup 2}, respectively. While La and Nd-doped SBTi samples display the maximum 2P {sub r} value of 18.4 and 19.1 {mu}C/cm{sup 2} with doping content of 0.05 and 0.10, respectively. The ferroelectric properties of Sr{sub 2}Bi{sub 4-} {sub x}Ln{sub x} Ti{sub 5}O{sub 18} are found to be dominated by the competition of the decrease of oxygen vacancy concentration and the relief of structural distortion. - Graphical abstract: The temperature dependence of the dielectric loss for (a) SBST, and (b) SBDT at 500 kHz. Display Omitted.

An investigation of the ferroelectric and dielectric properties of niobium-doped SrBi4Ti4O15 (SrBi4−x/3Ti4−xNbxO15, x = 0.00, 0.003, 0.012, 0.03, 0.06) ceramics was presented. The ferroelectric property of SrBi4Ti4O15 was improved by niobium doping. The remanent polarization (2Pr) increases at first, then decreases with the increase in niobium content, while the coercive field changes little with Nb-doping. As the niobium content is 0.03, the 2Pr maximizes at a value of 24.7 µC cm−2, which is increased by about 60% in comparison with that of SrBi4Ti4O15. The Curie temperature of the samples hardly varies upon Nb-doping, which indicates that the good thermal stability of SrBi4Ti4O15 does not deteriorate after Nb addition.

The ferroelectric ceramics of Bi{sub 4}Ti{sub 3}O{sub 12}, SrBi{sub 4}Ti{sub 4}O{sub 15}, and lanthanum-doped Bi{sub 4}Ti{sub 3}O{sub 12}-SrBi{sub 4}Ti{sub 4}O{sub 15} were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi{sub 4}Ti{sub 3}O{sub 12}-SrBi{sub 4}Ti{sub 4}O{sub 15}. The structure of the Bi{sub 2}O{sub 2} layers and TiO{sub 6} octahedra of the intergrowth was found to be different from those of Bi{sub 4}Ti{sub 3}O{sub 12} and SrBi{sub 4}Ti{sub 4}O{sub 15}. La{sup 3+} ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi{sub 2}O{sub 2} layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi{sub 4}Ti{sub 3}O{sub 12}-SrBi{sub 4}Ti{sub 4}O{sub 15}. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi{sub 2}O{sub 2} slabs.