X. M. Lu

Doping effect on the dielectric property in bismuth titanate

The dielectric property complemented by the mechanical measurement (internal friction) in the doped Bi4Ti3O12 [Bi4−xLaxTi3O12 (x=0.5,0.75,1) and Bi4−y/3Ti3−yNbyO12 (y=0.015,0.03,0.06)] was systematically investigated from room temperature to 350 °C. In the plot of dielectric loss versus temperature for Bi4Ti3O12 (BiT), a relaxation peak was confirmed to be associated with the motion of the oxygen vacancy. It is found that the La doping at site A is in favor of improvement of the fatigue property, in contrast, the Nb doping at site B can mainly enhance the remanent polarization. Appropriate La doping at site A of perovskite-type unit in BiT enhances the chemical stability of oxygen vacancy by improving the height of the potential barrier for hopping and enhances the mobility of domain by the changing of domain structures. While the Nb doping at site B could induce the distortion of oxygen octahedral and reduce the oxygen vacancy concentration by a compensating effect so that it results in an enhancement of...

Optical study on the size effects in BaTiO3 thin films

To study the size effects in ferroelectric thin film, we measured the optical transmittance and Raman spectra in BaTiO3 thin films deposited by the rf-magnetron sputtering technique on fused quartz and (111) Si substrates. A variation in the energy gap and Raman peaks with film thickness and grain size was observed and the possible origin was analyzed.

PULSED EXCIMER (KRF) LASER INDUCED CRYSTALLIZATION OF PBZR0.44TI0.56O3 AMORPHOUS FILMS

Amorphous PZT thin films 600 nm thick were rf sputtered from a PbZr0.44Ti0.56O3 ceramic target with excess PbO onto glass substrates maintained at room temperature. After irradiation with a 248 nm KrF pulsed excimer laser with a power density of 2.3×107 W/m2 at a frequency of 50 Hz and a pulsed width of 30 ns for 2 min, the films crystallized into the PZT perovskite structure to a depth of about 120 nm. Comparisons of this work with PZT crystallization obtained from a traditional oven and 488 nm Ar+ laser postdeposition treatments are also given.

The energy gap of r.f.-sputtered BaTiO3 thin films with different grain size

Abstract BaTiO 3 thin films were deposited using the r.f. magnetron sputtering technique on unheated fused quartz, poly-crystalline Pt and (111) Si substrates. The films with different grain sizes were obtained through post-deposition heat treatment. The optical transmittance of the films with different grain sizes on fused quartz substrates was measured and the observed shift of the energy gap with grain size was discussed.

La-doped effect on the ferroelectric properties of Bi4Ti3O12–SrBi4Ti4O15 thin film fabricated by pulsed laser deposition

Bi4Ti3O12–SrBi4Ti4O15 (BT–SBTi) thin film was fabricated successfully on Pt/TiO2/SiO2/Si(110) substrates by the pulsed laser deposition technique. Films annealed at 650 °C by the rapid temperature process (RTP) have Pr=12 μC/cm2. But, the fatigue behavior has been observed although no obvious decrease in Pr up to 105 s retained time in the BT–SBTi capacitor. After being La doped, the Bi3.25La0.75Ti3O12–SrBi4Ti4O15 (BLT–SBTi) has fatigue free properties. Pr=13.5 μC/cm2 was measured in a BLT–SBTi film of 300 nm thickness. It did not show any significant fatigue up to 1010 switching cycles above the applied field of 250 kV/cm. It also has good retention properties. The field dependence of fatigue behavior and La-doped effect are discussed.

Laser‐induced phase transformation from amorphous to perovskite in PbZr0.44Ti0.56O3 films with the substrate at room temperature

Radio‐frequency‐sputtered amorphous as‐grown PbZr0.44Ti0.56O3 (PZT) thin films were prepared on glass substrates from a PZT ceramic target with excess PbO. They were subsequently treated with a laser‐induced phase transformation technique to achieve a pure perovskite structure. The optimal conditions for the process were determined. During the whole fabrication process, the substrate was kept at room temperature. This technique was also compared with traditional oven and rapid thermal processing after‐deposition treatments.

Retention characteristics of SrBi2Ta2O9 thin films prepared by metalorganic decomposition

Polycrystalline SrBi2Ta2O9 (SBT) ferroelectric thin films were synthesized on Pt/Ti/SiO2/Si substrates by metalorganic decomposition. Electric measurements demonstrate that the polarization decay increases with increasing the write/read voltage within the first second. This could be attributed to the depolarization fields, which increases with increasing the retained polarization. However, we found that the polarization loss is insignificant with different write/read voltages over a range of 1–30 000 S. Furthermore, experiment indicates that there is weak pinning of domain walls existing in SBT, which plays an important role for SBT thin film over a range of 1–30 000 S with a low write/read voltage.

Study on the crystallization by an electrical resistance measurement in Ge2Sb2Te5 and N-doped Ge2Sb2Te5 films

An electric resistance measurement was used to study the crystallization process of Ge2Sb2Te5 (GST) and N-doped Ge2Sb2Te5 (N-GST) films. The relation between conductivity and annealing time was investigated and the crystallization parameters were determined directly by resistance measurement during isothermal crystallization process in the amorphous GST and the N-GST films. The results show that the crystallization processes in both GST and N-GST films are layer by layer. Their conductivities satisfy the equation σ=σc−(σc−σa)exp(−ktn), at t>τ, where τ is a temperature-dependent time in the process of crystallization. The activation energy for crystallization of amorphous GST films was 2.11±0.18eV and the Avrami coefficient was between 2 to 4, in close agreement with previous studies using different techniques. After N doping the Avrami coefficient decreased, while the activation energy increased. The formation of a strain induced by the distortion of unit cell after N doping was used to explain the observ...

Stress effects in ferroelectric thin films

An uneven distribution of stress in the thickness direction was introduced into Landau theory to investigate the behavior of phase transformations of ferroelectric thin films. Extensive stress induced a decrease of Curie temperature and polarization while an increase of susceptibility near the surface. Compressive stress induced an increase of Curie temperature and polarization and a decrease of susceptibility near the surface. There exist size-driven and stress-driven phase transformations only for the extensive stress cases.

Origin of magnetic anisotropy and spiral spin order in multiferroic BiFeO3

The first-principles calculations and thermodynamic modeling are combined to investigate the magnetic properties of BiFeO3. Our calculations indicate that the single-ion anisotropy and the anisotropic superexchange coupling contribute the same magnitude to the easy-magnetization-plane anisotropy. We show that the competition between the isotropic superexchange and the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)] of the nearest-neighbor Fe spins provides the microscopic mechanism for the origin of the long period spiral spin order, and the induced spontaneous magnetization exhibits a sinusoidal arrangement under the spiral order.