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The single Bi4-xEuxTi3O12 and Ni1-xCuxFe2O4 films were prepared via spin-coating method. The composite films of the Bi3.4Eu0.6Ti3O12/Ni0.7Cu0.3Fe2O4, annealed under N2, air and O2, were also prepared via the same method. Compared with the films of Bi4Ti3O12, the films of the Eu-doped Bi4Ti3O12 (Bi4-xEuxTi3O12) exhibit enhanced ferroelectricity. And when x is equal to 0.6, the films of Bi4-xEuxTi3O12 show optimal ferroelectricity. Compared with the undoped NiFe2O4 film, in the films of Ni1-xCuxFe2O4, the doping of Cu2+ enhances ferromagnetism. And when x is equal to 0.3, the Ni1-xCuxFe2O4 films exhibit optimal ferromagnetism. For the composite films of Bi3.4Eu0.6Ti3O12/Ni0.7Cu0.3Fe2O4, annealing atmosphere has a significant impact on the magnetoelectric properties. In comparison with the composite films annealed under N2 and air, the composite films annealed under O2 exhibit optimum ferroelectricity (saturation polarization being 26.3 μC·cm−2), ferromagnetism (saturation magnetization being 385.6 emu·cm−3) and enhanced magnetoelectric coupling effect (magnetoelectric voltage coefficient being 86.4 mV·(cm·Oe)−1). This is beneficial for the applications in magnetoelectric functional devices.

Lead-free films of Bi4-xNdxTi3O12 were deposited on Pt(111)/Ti/SiO2/Si(100) substrate via spin-coating methods. It is shown that there are no secondary phases in Bi4-xNdxTi3O12 films and clear interfaces between the Bi4-xNdxTi3O12 films and substrates when the films are annealed at 700 ℃. And the Bi4-xNdxTi3O12 films also exhibit a blue light emission peak at 437 nm and a yellow light emission peak at 580 nm. There are narrower band gaps, higher dielectric constant and lower dielectric loss when Nd3+ concentration varies from 0 to 0.85. And the Bi3.15Nd0.85Ti3O12 film possesses the minimum of band gap energy (2.67 eV). Moreover, Bi3.55Nd0.45Ti3O12 film exhibits a minimal leakage current density and a maximal remanent polarization, which is highly beneficial for the potential applications in multi-functional devices.

The films of (Bi0.5Na0.5)(Ti1-xMnx)O3-δ (BNTMx) were deposited on the substrates via the sol–gel method. The influence of the doping content of Mn on the microstructures and ferroelectric properties of the films were investigated. In addition, the valence states of Mn ions were analyzed. The results show that Mn ions have dissolved into the lattice of Bi0.5Na0.5TiO3 (BNT) without forming any secondary phase. When the doping content of Mn is 0.04, the film of BNTMx possesses a dense microstructure, maximum of remnant polarization (20.2 µC·cm−2), minimum value of leakage current density (3.31 × 10–5 A· cm−2), which shows good ferroelectric property and insulation performance. The results of XPS indicate that Mn ions exist in form of Mn2+, Mn3+ and Mn4+. The ratio of the amount of Mn4+ to that of Mn3+ and Mn2+ is 5.5:1. In this work, relationship between valence states of Mn ions and leakage current densities or ferroelectric property of the films were investigated in detail. The results will provide a new way for future applications of BNT-based multi-functional devices and an alternative for environmental-friendly ferroelectric materials.

The magnetoelectric composite films of Bi3.15Nd0.85Ti2.9Zr0.1O12 (BNTZO)–CoFe2O4 (CFO) were deposited on the substrates of Pt/Ti/SiO2/Si (111) by means of the sol–gel method. The results show that, in the composite films, there are tri-axial compressive stresses in the CFO films. Nevertheless, there are bi-axial tensile stresses and uniaxial compressive stress in the BNTZO films. The composite films possess compact microstructure and flat interface without forming intermediate layer. The composite films have good magnetoelectric properties besides both good ferroelectric and ferromagnetic properties. When Hdc is 738 Oe, the composite film of BNTZO-CFO possesses the maximum of αE, 114 mV cm−1 Oe−1, which is helpful for the application in multi-functional devices.

In this study, the films of Bi4−xEuxTi3O12 (x = 0, 0.2, 0.4, 0.6, 0.8) were prepared on substrates (Pt(111)/Ti/SiO2/Si(100)) by the spin-coating method. The results indicate that the films of Bi4−xEuxTi3O12 annealed at 700 °C consist of Bi4Ti3O12 and Pt from the substrates. This indicates that Eu3+ has dissolved into the lattice of Bi4Ti3O12. The doping of Eu3+ to the films of Bi4Ti3O12 enhances ferroelectric properties as well as photoluminescent properties. The films of Bi4−xEuxTi3O12 show two orange emission perks at 590 nm and 595 nm, and a red emission at 613 nm. These three peaks are ascribed to 5D0 → 7F0, 5D0 → 7F1, and 5D0 → 7F2, respectively. The bandgaps of the films of Bi4−xEuxTi3O12 range from 3.07 eV to 2.86 eV with the increase of the doping concentration of Eu3+. Bi3.4Eu0.6Ti3O12 film possesses maximal remanent polarization, minimal leakage current density, and greatest emission intensity.