Papers by Author: Z.M. Wan

Abstract: Tb4O7-doped bismuth titanate (BixTbyTi3O12 BTT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the microstructures and ferroelectric properties of the films were investigated. Microstructure studies indicate that all of BTT films with well-developed rod-like grains consist of single phase of a bismuth-layered structure without preferred orientation. The experimental results indicate that Tb doping into Bi4Ti3O12 results in a remarkable improvement in ferroelectric properties. The remanent polarization (Pr) and coercive field (Ec) of the BTT film with y=0.6 were 22 μC/cm2 and 85 kV/cm, respectively.

Abstract: Pr6O11-doped bismuth titanate (BixPryTi3O12: BPT) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BPT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with y=0.06, 0.3, 1.2 and 1.5, ferroelectric hysteresis loops were characterized by large leakage current, whereas for samples with y=0.6 and 0.9, ferroelectric hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT Film with y=0.9 were above 35μC/cm2 and 80KV/cm , respectively. After 3×1010 switching cycles, 20% degradation of 2Pr is observed in the film with y=0.9.

Abstract: Pr6O11-doped bismuth titanate and random oriented BixPryTi3O12 ( y = 0.3, 0.6, 0.9, 1.2) thin films were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. Pr doping into BIT caused a shift of the Curie temperature (TC) of the BIT from 675°C to 578 , 517, 398 , and 315oC for the films with y = 0.3, 0.6, 0.9, and 1.2, respectively. The experimental results indicated that Pr doping into BIT result in a remarkable improvement in dielectric properties. Raman analysis shows that Pr3+ and Pr4+ ions substitution only appears in A-sit.

Abstract: Nd-doped bismuth titanate and random oriented Bi4-xNdxTi3O12 (BNT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique. These samples had polycrystalline Bi-layered perovskite structure without preferred orientation, and consisted of well developed rod-like grains with random orientation. The remanent polarization (Pr) and coercive field (Ec) of the BNT film with x = 0.5 were above 19 μC/cm2 and 50 KV/cm, respectively. Nd doping into BIT caused a shift of the Curie temperature (TC) of the BIT from 675°C to 660, 520, 410 and 256oC for the films with x = 0.25, 0.5, 0.75 and 1.0, respectively. The experimental results indicated that Nd doping into BIT result in a remarkable improvement in ferroelectric and dielectric properties.

Abstract: The electrical properties of Gd-doped bismuth titanates (Bi3.25Gd0.75Ti3O12, BGT) prepared by a conventional ceramic technique have been investigated. At applied d.c. field below 200V/mm, the current-voltage curve of the BGT ceramic exhibits a negative differential resistance behavior. The impedance spectrum indicates that the sample consists of semiconducting grain and moderately insulating grain boundary regions. XRD, SEM and EPMA analyses reveal crystalline phase characterized by a Bi-layered perovskite structure of Bi4Ti3O12 (BIT) and the distribution of every element is uniform. The BGT sample exhibits randomly oriented and plate-like morphology.

Abstract: Nd-doped bismuth titanate Bi4-xNdxTi3O12 (BNT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel method and spin-coating technique. The structures and the ferroelectric properties of the films were investigated. Nd doping leads to a marked improvement in the remanent polarization (Pr) and the coercive field (Ec). At the applied electric field of 260 kV/cm, Pr and Ec of the BNT film with x=0.5 annealed at 650oC are 19 μC/cm2 and 135 kV/cm, respectively. Moreover, the BNT film with x=0.5 showed a fatiguefree behavior up to 3×1010 read/write cycles.