Oxygen Stability and Leakage Current Mechanism in Ferroelectric La-Substituted Bi₄Ti₃O₁₂ Single Crystals

Abstract

We have investigated the effects of La substitution on the oxygen stability, defects, leakage current and polarization properties in ferroelectric bismuth titanate (Bi4Ti3O12) by measuring the properties of single crystals and by ab initio electronic structure calculations. It is shown that electron holes arising from the incorporation of oxygen at oxygen vacancies act as detrimental carriers for leakage current at room temperature for the crystals of BiT and La-substituted BiT. La substitution is effective for reducing oxygen vacancies and thus electron holes, which is attributed to an excellent insulating property observed for La-substituted crystals. High-pressure oxygen annealing is demonstrated to improve the remanent polarization of La-substituted crystals.

Wide bandgap tunability in complex transition metal oxides by site-specific substitution

“…Nevertheless, the impact of Co on the bandgap change is amazingly large as discussed later. Moreover, it has been reported that O vacancies readily form in the Aurivillius structure and prefer sites near the Bi 2 O 2 layer, without compromising the ferroelectricity 17,22,23 . Therefore, further considering the difference in ionic size as well as electronegativity, we presume that Co preferentially substitutes for Ti next to the Bi 2 O 2 layer accompanying O vacancies to compensate valence difference.…”

High-quality single crystal growth of Bi-based perovskite ferroelectrics based on defect chemistry

“…Noguchi et al 108), 109) have indicated that the vacancy formation of Bi proceeds preferentially in the perovskite layers rather than in the Bi2O2 layers. The reaction of the vacancy formation (Eq.…”

Optical anisotropy in bismuth titanate: An experimental and theoretical study

“…4 At Curie temperature (T c ¼ 948 K), ferroelectric BiT transforms into a paraelectric phase with centrosymmetric tetragonal (I4/mmm) structure having lattice parameters, a ¼ b ¼ 3.8524 Å and c ¼ 33.197 Å . 23 Noncentrosymmetry of the room temperature structure along with its complexity further renders anisotropic physical properties in the material, namely dielectric constant (e a ¼ e b ¼ 153 6 5 and e c ¼ 118 6 5 at 100 kHz), 6 ferroelectric polarization, 15,24 and thermal 25 and electrical 23,26 conductivities. It is interesting to note that anisotropy in different physical properties have different origins.…”