Yi Kan

Effect of Nd dopant on magnetic and electric properties of BiFeO3 thin films prepared by metal organic deposition method

Polycrystalline Bi1−xNdxFeO3 (x=0–0.15) thin films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic deposition method. The effect of Nd dopant on the structural, electric, and magnetic properties was studied. It was found that the ferroelectric polarization and saturation magnetization of the films were enhanced by appropriate Nd doping due to the structural distortion and the suppressed cycloidal spin structure. Meanwhile, Nd-doped BiFeO3 thin films exhibited magnetic anisotropy because of the magnetocrystalline anisotropy.

Oxygen-vacancy-related high-temperature dielectric relaxation in SrTiO3 ceramics

Quantum paraelectric SrTiO3 has resulted in many investigations because of the anomalous properties. Here, using the conventional solid-state reaction method, we fabricated polycrystalline SrTiO3 ceramics with pure cubic perovskite structure. A dielectric loss peak is observed at around 450 K and 100 Hz and it shifts to higher temperature with increasing frequency. The typical high-temperature dielectric relaxation process is confirmed to be related to the oxygen vacancies (OVs) inside ceramics. More interestingly, a Cole–Cole fitting to loss peaks reveals a weaker correlation among OVs for such dielectric materials compared with that of ferroelectrics.

Multiferroic properties and dielectric relaxation of BiFeO3∕Bi3.25La0.75Ti3O12 double-layered thin films

BiFeO3 (BFO)∕Bi3.25La0.75Ti3O12 (BLT) films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic decomposition method. The multiferroic and dielectric properties of the films were studied. It was found that the ferroelectric polarization and dielectric constant of the films were enhanced by introducing BLT as a barrier layer between BFO and Pt bottom electrode, while the ferromagnetism of BFO was not influenced. More interestingly, the films showed dielectric relaxor behavior, and the possible causes of which were discussed.

Domain reversal and relaxation in LiNbO3 single crystals studied by piezoresponse force microscope

The LiNbO3 crystal was polarized and characterized by the piezoresponse force mode of scanning probe microscope. By using the Kolmogorov-Avrami-Ishibashi [Izv. Akad. Nauk, USSR: Ser. Math. 3, 355 (1937); J. Chem. Phys. 8, 212 (1940); J. Phys. Soc. Jpn. 63, 1031 (1994); 63, 1601 (1994)] theory to analyze the relaxation process after domain switching, it was found that (1) the percent of final switched domains after poling increased with the enhancing poling voltage, (2) the nucleation time was a constant to a certain sample, (3) the dimension of domain growth decreased with the enhancing poling voltage, and (4) the relaxation time had a maximum at a medial voltage. The corresponding mechanism for domain switching was discussed, which is hopefully useful for domain engineering.

Critical radii of ferroelectric domains for different decay processes in LiNbO3 crystals

The LiNbO3 crystals were polarized at fixed points and characterized by means of scanning probe microscope. The growth evolution and the decay process of the fabricated domains were carefully studied. Two critical radii rC and Rc that determine a different decay behavior of domains were put forward, where rC is considered to correspond to the point when the domains just penetrate the crystal. Those domains with radius larger than rC could exist beyond 5days, those between rC and Rc experienced a distinct metastable state before completely disappearing, while those smaller than Rc were even invisible under piezoresponse force mode.

Tunable electric properties of PbZrO3 films related to the coexistence of ferroelectricity and antiferroelectricity at room temperature

Polycrystalline PbZrO3 films with a preferred orientation were fabricated via the metal-organic decomposition method. For heat-treated PbZrO3 films, the P-E hysteresis loops, dielectric spectra, and I-V curves show interesting changes with time, which strongly suggest the coexistence of antiferroelectric and ferroelectric phases at room temperature. Based on the easy transition between these two phases, the electric properties of the films become tunable. A dielectric tunability of about 50.2% below 8.2 V makes it a promising low working-voltage dielectric tunable material, and the significant current change of four orders of magnitude indicates potential application as a voltage-controlled rheostat.

Thickness-dependent structural and magnetic properties of BiFeO3 films prepared by metal organic decomposition method

Perovskite BiFeO3 films with various thicknesses were prepared on Pt/Ti/SiO2/Si substrates by metal organic decomposition method. It was found that, with the film thickness increasing from 35 to 120 nm, the grain and ferroelectric domain size slightly increased, while the saturation magnetization Ms abruptly decreased. For the further increase of film thickness, Ms decreased slowly and the magnetization of unit area exhibited a fluctuation behavior. Moreover, the magnetic anisotropy degenerated with the increase of film thickness. The possible causes for the thickness effects were discussed.

Magnetic and magnetodielectric properties of Y3−xLaxFe5O12 ceramics

Y3−xLaxFe5O12 (x = 0–0.5) ceramics with garnet structure are prepared by the solid state reaction method and their structural, magnetic, and magnetodielectric properties are investigated systematically. La3+ substitution leads to lattice expansion and possible ion transposition, which oppositely affect the variation of Fe2+ concentration. As a result, both the saturation magnetization and the intrinsic magnetodielectric effect first increase and then decrease with the increase of La concentration. More interestingly, room temperature large magnetodielectric coefficient of about −5% is obtained at 106 Hz and 0.9 T for Y2.7La0.3Fe5O12 ceramics. This study provides a feasible alternative method for modulating the saturation magnetization and the magnetodielectric effect of Y3Fe5O12-based materials.

Nonmonotonic variation of aging behavior in Fe-doped BaTiO3 ceramics

The investigation of ferroelectric aging effect in Fe-doped BaTiO3 ceramics reveals that such effect is first strengthened and then suppressed with the increase content of Fe dopant. Such nonmonotonic variation of aging behavior is considered to be originated from the competition effects between increased concentration of oxygen vacancies and decreased c/a value on the formation of defect dipoles (FeTi′−Vo··)·. This study provides a feasible alternative method for modulating aging effect and will favor the applications of ferroelectrics.

Stress effects on ferroelectric and fatigue properties of Nd- and La-doped Bi4Ti3O12 thin films

The ferroelectric properties of Bi3.15Nd0.85Ti3O12 and Bi3.25La0.75Ti3O12 thin films under applied uniaxial stress were investigated. It was observed in both films that the remnant polarization (Pr) increased with tensile stress, while it decreased with compressive stress. On the contrary, the coercive field (Ec) decreased with the stress changing from maximum compression to maximum tension. Fatigue behavior of the films was improved under either compressive or tensile stress compared with zero stress (free state). These results can be well explained in the scenario of domain reorientation under stress; however, the polarization-strain coupling mechanism could not be simply ruled out.