Jae Yun Yi

Dependence of incommensurate phase formation on vacancy type in La-doped (Na1/2Ba1/2)TiO3

Changes in structure and phase transition behavior are investigated for two types of La-doped sodium bismuth titanate ceramics. When A-site vacancies are formed by La incorporation, the phase transition near 200 °C becomes pronounced. Hysteresis loop and e(T) demonstrate that the structure above 200 °C is the incommensurate antiferroelectric phase. In contrast, B-site vacancies produced by La doping do not contribute to the incommensurate phase. The origin for the formation of the incommensurate antiferroelectric state between the rhombohedral ferroelectric phase and tetragonal paraelectric phase is discussed in a view of decoupling effects due to the A-site vacancies.

Substrate Temperature Dependence of Phase and Orientation of Pulsed Laser Deposited Bi-La-Ti-O Thin Films

Bi3.25La0.75Ti3O12 (BLT) thin films were grown by pulsed laser deposition at substrate temperatures ranging from 400 to 800°C. The phase, orientation, and surface morphology of the deposited films were investigated in order to understand the deposition behavior of the BLT films. As the substrate temperature was increased to 800°C, the films showed a tendency to grow with c-axis preferred orientation and a rough surface. At lower substrate temperatures, however, polycrystalline BLT films were formed. In addition, at the lowest substrate temperature of 400°C, the film consisted mostly of a nonferroelectric fluorite-like phase. This was attributed to the difficulty in forming a perfectly layered structure. The fluorite-like phase was transformed to a ferroelectric polycrystalline BLT phase through annealing in flowing oxygen at 600°C.

Domain configuration and crystal structure of Pb(Zn1/3Nb2/3)O3–5%PbTiO3 crystals as a function of the electric-field direction

The domain configuration of 0.95Pb(Zn1/3Nb2/3)O3–0.05PbTiO3 single crystals was investigated as a function of the applied electric-field direction with respect to the crystallographic orientation. A normal ferroelectric domain structure, which was not observable in virgin crystals (not exposed to electric field), appeared upon the electric-field (E-field) induced transition from the relaxor state to the normal ferroelectric state. After E-field was applied along the polar 〈111〉 direction and removed, a band-shaped domain configuration appeared as a result of subsequent depolarization. The depoled 〈111〉 crystal consisted of predominantly (110) domain boundaries, which represents the minimum energy domain state in rhombohedral ferroelectrics. In contrast, crystals must transform into the phase with the symmetry lower than rhombohedral, i.e., monoclinic structure, by an E-field application along 〈001〉. Domain boundaries in 〈001〉 poled crystals were indexed to be (001), being a favorable state for monoclinic ...

Physical mechanism for orientation dependence of ferroelectric fatigue in Pb(Zn1∕3Nb2∕3)O3‐5%PbTiO3 crystals

The underlying phenomenology of the crystallographic orientation dependence on ferroelectric fatigue behavior was investigated in rhombohedral Pb(Zn1∕3Nb2∕3)O3‐5%PbTiO3 (PZN-5PT) crystals. It was recently found that an electric field (E field) application along the ⟨001⟩ direction of PZN-5PT crystal did not induce the fatigue to 105cycles of bipolar electric field cycling (switching), while the ferroelectric fatigue became evident from 103cycles of polarization switching along the ⟨111⟩ direction. In this study, the dependence of ferroelectric fatigue on the crystal orientation is explained by changes in internal stress, switching mechanisms, and domain configuration. The magnitude of the in-plane tensile strain was a maximum during a domain switching in ⟨111⟩ oriented crystals, resulting in the suppressed motion of domain boundaries in ⟨111⟩ oriented crystals. In addition to the stress, differences in domain switching mechanisms and domain boundary density for ⟨001⟩ and ⟨111⟩ oriented crystals contribute...

Relationship between Structure and Dielectric Property in (1-x)(Na1/2Bi1/2)TiO3–xPbZrO3 Ceramics

The effect that PbZrO3 (PZ) addition to (Na1/2Bi1/2)TiO3 (NBT) has on crystal structure, domain state, ferroelectric property and cation ordering was investigated. With increasing PZ concentration, lattice distortion of NBT decreased and the phase transition behavior became similar to that of relaxor ferroelectrics. The relaxor-like behavior was maximum in a NBT–0.5PZ ceramics, whose phase transition behavior and ferroelectric hysteresis loop were those of typical relaxor ferroelectrics. These variations were discussed in terms of cation ordering and local fields. Structural analysis using transmission electron microscope (TEM) revealed that PZ addition prevented the arrangement of A-site cations, which caused random fields and non-uniform polarization in NBT–PZ solid solution.

Stabilized antiferroelectric phase in lanthanum-doped (Na1/2Bi1/2)TiO3

Phase transition behaviour of La-modified sodium bismuth titanate ceramics [(Na0.5Bi0.5)1−1.5xV0.5xLax]TiO3 (NBLT) was investigated. The two anomalies in er(T) and DSC analysis indicated that lower temperature phase transitions below 200 °C became pronounced with La additions. The polarization relaxation of er(T) and double hysteresis loops showed that the intermediate region between two dielectric anomalies was the antiferroelectric modulated phase. The origin of the modulated antiferroelectric state was discussed in terms of disordering effects of the La ions and cation vacancies. With increasing La content, the long-range symmetry of the dipoles in the ferroelectric phase was disturbed in the intermediate region. The competition between rhombohedral ferroelectric phase and tetragonal paraelectric phase contributed to the formation of a modulated antiferroelectric phase in NBLT ceramics.

Polarization Switching in Pb(Zn1/3Nb2/3)O3–5%PbTiO3 Crystals

The polarization switching mechanism as a function of crystallographic orientation in Pb(Zn1/3Nb2/3)O3–5%PbTiO3 (PZN–5%PT) single crystals was investigated using the switching current measurement technique. Both the activation E-field and the critical pulse width were greater if E-field for polarization switching was applied along the polar axis than applied along . The sideward growth was dominant in domain switching of oriented crystals. The dominance of the nucleation and forward growth behavior was observed in oriented crystals. The nucleation probability of reverse polarized domains is expected to be much greater in crystals than in crystals, being ascribed to the lower projected polarization value along the E-field direction, higher domain wall energy associated with the pseudo-monoclinic structure of domains, and large domain wall density as a consequence of averaged domain configuration. This domain switching anisotropy may be one of the origins of the fatigue anisotropy.

Correlation between cation vacancies and phase transition behavior in La-modified sodium bismuth titanate

In this study, the influence of cation vacancy on phase transition was investigated with the aid of dielectric spectroscopy. La ions were incorporated into (NBT) to cause A site vacancy (named as NBLT-A) or B site vacancy (named as NBLT-B). In NBLT-A, La modification reduced the degree of cation ordering in A-site and caused a dielectric relaxation in a transition from ferroelectric commensurate phase to incommensurate phase. However, NBLT-B (x=0.05) shows only diffuse phase transition between paraelectric and ferroelectric phase. The phenomenon was discussed in terms of the role of A-site cation ordering and vacancies on translational symmetry of dipoles.