| In this paper, Nd, Sm, Pr, Gd, Dy and W doped bismuth titanate ceramics were prepared by a conventional electroceramic technique. In addition, Nd and Pr doped bismuth titanate films with random orientation were also fabricated on (111) Pt/TiO2/SiO2/Si by Pulsed Laser Deposition (PLD) method. The microstructures, chemical compositions, and electrical properties of samples with various parameters have been investigated thoroughly and described in brief as follows:(1) XRD patterns of the rare-earth ions doped ceramics and films indicate that all these samples have a single-phased bismuth-layered structure corresponding to Bi4Ti3O12. We thus conclude that Bi-layered structure is insensitive to the amount of rare-earth ions. On the other hand, the microstructure of W-doped bismuth titanate ceramic is found to be completely different from that of rare-earth ions doped ceramics.(2) The morphologies of ceramic and film samples were investigated. SEM patterns of ceramic samples always show the plate-like morphology, i.e., the doped amount and rare-earth element do not affect the size of plate-like grain. For film samples, however, rod-like or globose grains with sizes much smaller than their ceramic counterparts are found from SEM micrographs. Furthermore, the size and shape of these grains are influenced by doped amount, doped element, and processing parameters, such as laser energy flux, annealing temperature, and oxygen pressure. In addition, cuboidal and globose grains with a size distribution are found in W-doped bismuth titanate ceramics, which may be due to the coexistence of two phases.(3) Obviously, the ferroelectric and electrical properties of BIT depend on the doped rare-earth element, doped concentration, and processing parameters. Nd-, Sm- and Pr-doped bismuth titanate ceramics with the highest ferroelectricity are Bi3.5Nd0.5Ti3O12, Bi3.2Sm0.8Ti3O12 and Bi2.9Pr0.9Ti3O12, and their remanent polarization and coercive field are 20μC/cm2 and 50kV/cm, 16μC/cm2 and 70kV/cm, and 30μC/cm2 and 52kV/cm, respectively. Meanwhile, a dramatic improvement of ferroelectric property is found in Nd and Pr doped BIT films. The optimized remanent polarization and coercive field are 18.5μC/cm2 and 52kV/cm for Bi3.5Nd0.5Ti3O12 film, 29μC/cm2 and 58kV/cm for Bi2.9Pr0.9Ti3O12 film. Both Ec of Bi3.5Nd0.5Ti3O12 and Bi2.9Pr0.9Ti3O12 films are comparable with that of Bi3.25La0.75Ti3O12 film; while those of Pr are much larger than that of Bi3.25La0.75Ti3O12 film.(4) The current-voltage (I-V) characteristic of doped Bi4Ti3O12 ceamics at low field (E≤100V/mm) indicates that rare-earth doping has an important effect on I-V curves. The symmetric voltage-controlled negative differential resistance (VNDR) behavior of BIT evolves into asymmetric VNDR behavior, some even into the ohmic conductivity. It is found that the rare-earth doped ceamics with VNDR characteristic have high ferroelectricity (excepting Gd doped), but those with ohmic conductivity show no ferroelectricity. In addition, the I-V characteristic of W-doped ceramic exhibits an ohmic-fluctuation-stable nonlear behavior that increases with temperature. (5) The dependence of chemical composition, dielectric property, leakage-current density, and remanent polarization on doping concentration indicates that the amount of Bi doping into BIT ceamics and films is of crucial for the ferroelectric, dielectric, and leakage-current properties.(6) The fatigue characteristics of Nd- and Pr-doped BIT films were also studied. No fatigue is observed for Bi3.5Nd0.5Ti3O12 and Bi2.9Pr0.9Ti3O12 films after 3×1010 switching cycles at 1MHz. After being switched up to 3×1010 cycles at 1kHz, however, 2Pr is found a 20% degradation for Bi3.5Nd0.5Ti3O12 film, and a 10% degradation for Bi2.9Pr0.9Ti3O12 film.
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