Y. W. Li

Structural, ferroelectric, dielectric, and magnetic properties of BiFeO3∕Pb(Zr0.5,Ti0.5)O3 multilayer films derived by chemical solution deposition

BiFeO3∕Pb(Zr0.5,Ti0.5)O3 (BFO/PZT) multilayer films have been grown on platinum-coated silicon substrate by chemical solution deposition. The remnant polarization is about 12μC∕cm2, which is much bigger than most of pure BFO thin films. P-E measurement shows that there are more obstacles affecting the motion of the domain wall in the multilayer films than those in the pure PZT films. This conclusion is also confirmed by measuring the dependence of capacitance with ac field under subswitching field. The frequency dependence of dielectric loss indicates that the dielectric loss (tanδ) of the multilayer is smaller than that of the PZT thin films at high frequency. Magnetic measurement indicates that the multilayer films are antiferromagnetic.

Temperature dependent phonon Raman scattering of highly a-axis oriented CoFe2O4 inverse spinel ferromagnetic films grown by pulsed laser deposition

Lattice vibrations of highly a-axis oriented CoFe2O4 (CFO) films have been investigated by Raman scattering in the temperature range of 80-873 K. The five phonon modes T1 g (2), T1 g (3), E g , A1 g (1), A1 g (2), and their evolutions can be uniquely distinguished. It was found that an electron transfer between Co2+ and Fe3+ cations occurs in octahedral sites at about 173 K. The structure disorder in the CFO films appears with increasing the temperature, which indicates the cation migration between tetrahedral and octahedral sites. The phenomena suggest the structural transformation trend from inverse spinel to normal spinel at the elevated temperatures.

Structural and optical properties of Ba(Cox,Ti1−x)O3 thin films fabricatedby sol-gel process

Ba(Cox,Ti1−x)O3 thin films were prepared on fused quartz substrate by a sol-gel method. The results of x-ray diffraction showed that the films are perovskite phase and the change of lattice constant caused by different Co concentration is undetectable. Optical transmittance measurement indicated that Co doping has effect on the energy band structure. The energy gap of Ba(Cox,Ti1−x)O3 decreased linearly with the increase of Co concentration. It is inferred that the energy level of conduction bands decline with the Co content increasing. This result is similar to the phenomena found in binary semiconductor where the band gap decreases with the increasing of average atomic number.

Temperature dependence of terahertz optical characteristics and carrier transport dynamics in p-type transparent conductive CuCr1−xMgxO2 semiconductor films

Terahertz reflectance spectra and electrical transport of CuCr1− x Mg x O2 films have been studied in temperature range of 150–300 K. With increasing temperature, the phonon mode near 15 THz shows a redshift trend, and free carrier absorption below 6 THz becomes more prominent. Moreover, hole effective mass increases linearly from 0.028 to 0.48 m 0 with the temperature and composition. Hall coefficient shows a turning-point at about 220, 206, and 194 K for the composition of x = 0.02, 0.06, and 0.10, respectively. The phenomena can be attributed to the transition of carrier transport mechanism from a thermal activation behavior to a variable range-hopping one.

Enhanced Raman scattering and photoluminescence of Bi3.25La0.75Ti3O12 nanotube arrays for optical and ferroelectric multifunctional applications

Raman scattering enhancement has been observed from highly ordered ferroelectric Bi 3.25 La 0.75 Ti 3 O 12 nanotube (BLT-NT) arrays prepared by a template-assisted method. Scattering enhancement factor which is the ratio of average Raman intensity per molecule for nanostructure and film is evaluated to be about 92, 257, and 623 corresponding to the outer diameters of 50, 100, and 200 nm, respectively. The phenomena can be attributed to unique surface, microstructure, grain size, and tensile stress in the curved nanotube walls. These results indicate that BLT-NT arrays are suitable for fabricating multifunctional devices due to remaining good ferroelectricity.

Temperature dependent near infrared ultraviolet range dielectric functions of nanocrystalline (Na0.5Bi0.5)1−xCex(Ti0.99Fe0.01)O3 films

Optical properties and phase transition of Ce-modified (Na 0.5Bi0.5)(Ti0.99Fe0.01)O3 nanocrystalline films have been investigated by spectroscopic ellipsometry from −70 to 500 °C. Temperature dependent dielectric functions in the photon energy range of 0.6–6.4 eV can be derived by the Tauc-Lorentz model. It was found that the features in dielectric function (e) showed an abrupt variation near 200 and 340 °C, respectively. The phenomena can be explained by the appearance and/or reversal of polarization. It indicates that ferroelectric (rhombohedral) to paraelectric (tetragonal) phase transition is related to electronic band variation, which is observed by this technique.