Chaodan Zheng

Effect of precursor solution concentration on the grain orientation of Bi3.15Nd0.85Ti3O12 thin films

Polycrystalline Bi3.15Nd0.85Ti3O12 (BNT) thin films were fabricated on Pt/Ti/SiO2/Si by the sol–gel method. The dependence of precursor solution concentration (PSC) on the grain orientation of the films was observed, and a model was proposed to explain it by taking into account the effect of bulk nucleation. With increasing PSC, the BNT thin film turned from c-axis-preferential-oriented to random-oriented. It is suggested that a competition exists between the nucleation and grain growth on the grain orientation. When the PSC is low, the former plays a predominant role, while in the opposite case, the latter is dominant. The bulk nucleation inhibits the homoepitaxial grain growth, and it gradually replaces the heterogeneous nucleation as the main nucleation mechanism with the increase in PSC.

Hysteresis loops of first-order ferroelectric bilayers or superlattices and their size effect

Based on Landau–Ginzburg phenomenological theory, a first-order ferroelectric bilayer or superlattice with an antiferroelectric interface coupling has been studied by taking into account the spatial variation of polarization within each constituent film and the surface effect. The hysteresis loops are obtained and the size effect of a bilayer is discussed. The loop patterns vary between typically antiferroelectric and typically ferroelectric depending on the thickness ratio, the coupling constant, the thickness and the extrapolation length. The antiferroelectric coupling has a great effect on the phase transition of a bilayer. It is shown that the size-driven phase transition cannot be observed in a ferroelectric bilayer in the case of strong antiferroelectric coupling.

FERROELECTRIC PROPERTIES OF Zr-DOPED Bi3.25La0.75Ti3O12 THIN FILM DEPOSITED BY RF MAGNETRON SPUTTERING

ABSTRACT Thin films of Bi3.25La0.75Ti3O12 (BLT) and B-site substituted BLT by Zr, i.e. Bi3.25La0.75Ti3−x Zr x O12 (BLTZx, x = 0.20, 0.50, 0.75, 1.00 and 1.50) were fabricated on Pt/TiO2/SiO2/Si substrates by RF magnetron sputtering method. Effect of Zr4+ amount on the microstructure and ferroelectric characteristics of the thin film BLTZx were investigated. X-ray diffraction shows that A-site La3+ and B-site Zr4+ co-substitution do not destroy the layered perovskite structure. Compared with the well-known BLT thin films, appropriate Zr4+ added, such as the BLTZ0.20 thin film, has larger remnant polarization (2Pr) and better fatigue resistance. However, with further increasing Zr4+-doping concentration, the remnant polarization (2Pr) tends to decrease. When x > 0.75 the remnant polarization become lower than that of BLT thin film. The remnant polarization (2Pr) of the BLTZx thin films under the 12 V were 17.8, 25.6, 22.4, 17.2, 11.6, 10.2 μC/cm2, respectively, for x = 0, 0.20, 0.50, 0.75, 1.00 and 1.50, whereas there are almost no obvious difference in the Vc values.