Xinyi Chen

Fatigue 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 fatigue increases with decreasing switching voltage and frequency, and the suppressed polarization caused at a lower switching voltage can be recovered by switching at a higher voltage. This suggests that the domain walls of SBT thin films are weakly pinned and easily depinned by a higher external field. The polarization of SBT thin films annealed in air shows more degradation than that annealed in oxygen, which indicates that the oxygen vacancy also plays an important role in fatigue behavior of SBT thin films.

Enhancement of photoelectric conversion properties of SrTiO3/α-Fe2O3 heterojunction photoanode

The semiconductor films of SrTiO3, ?-Fe2O3 and their heterojunction SrTiO3/?-Fe2O3 were prepared on FTO (SnO2?:?F on glass) substrates by the spin-coating method and their structures and properties were characterized by XRD, SEM and photoelectrochemical measurements, respectively. It was observed that the photocurrent and the incident photon to current conversion efficiencies (IPCE or external quantum efficiencies) of the SrTiO3/?-Fe2O3 heterojunction were higher than that of the single SrTiO3 or ?-Fe2O3 film, particularly under visible light irradiation. The band structures of SrTiO3 and ?-Fe2O3 were calculated. It was found that the charge carriers in ?-Fe2O3 had large effective masses while the charge carriers in SrTiO3 had small effective masses at the bottom of the conduction band and at the top of the valence band, which meant weak mobility of holes photo-generated in ?-Fe2O3 and strong mobility of holes excited in SrTiO3. As to the SrTiO3/?-Fe2O3 heterojunction, the special valence band structures of SrTiO3 improved the separation efficiency of charge carriers which had been photo-generated in ?-Fe2O3. This led to the enhancement of photocurrent densities and external quantum efficiencies in the SrTiO3/?-Fe2O3 heterojunction photoanode.

Preparation of sensitized ZnS and its photocatalytic activity under visible light irradiation

In this paper, sensitized ZnS with visible light driven photocatlytic ability was successfully prepared. The obtained ZnS was characterized by x-ray diffraction, UV–visible diffuse reflectance spectra and Fourier transform infrared spectra. The photocatalytic property of the prepared ZnS was evaluated by decomposing methyl orange (MO). These sensitized ZnS powders with a proper molar ratio showed higher photocatalytic activity than TiO2(P25) under visible light (λ > 420 nm) irradiation. A possible explanation for the visible light activity of the prepared ZnS was proposed.

Photocatalytic Degradation of Acetaldehyde on Mesoporous TiO2: Effects of Surface Area and Crystallinity on the Photocatalytic Activity

Mesoporous TiO2 powder and films with worm-like channels were synthesized by an evaporation-induced self-assembly approach. The as-prepared samples were calcined at different temperature to investigate the effect of calcined temperature on the mesostructure and the photocatalytic activity. Acetaldehyde photodegradation in gas phase was employed to evaluate the photocatalytic activity of mesoporous TiO2. Results showed that all the calcined powder samples exhibited higher photocatalytic activities than that of Degussa P25. The sample calcined at 400C, which showed higher activity than other samples, possessed a homogeneous pore diameter of about 6.0 nm and an 11.0 nm crystalline anatase pore wall, as well as large surface area of 117 m2/g. It was speculated that two factors of surface area and crystallinity affected the photocatalytic activity of mesoporous TiO2 photocatalyst. The mesoporous TiO2 films fabricated by spin-coating also had high photocatalytic activities.

Switching properties of SrBi2Ta2O9 thin films produced by metalorganic decomposition

The process of polarization reversal in a SrBi2Ta2O9 (SBT) thin film capacitor produced by a metalorganic decomposition method was investigated. The switching time (100–600 ns) and the reversible polarization have been measured at different voltages in the range of 0–5 V. It was found that by annealing the SBT sample in AR atmosphere at 400u200a°C, the switching times were significantly reduced. This indicates that oxygen vacancies in the film speed up nucleation and growth of new domains.

Dielectric Relaxation and Internal Friction Related to the Mobility of Domain Wall in PZT Ferroelectrics

The dielectric permittivity of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) ceramics as a function of temperature was measured in the frequency range from 1 to 10 kHz. There exists a dielectric loss peak close to and below the Curie point, the height of which decreases as frequency increases. Although the peak moves towards higher temperatures with increasing frequency, the relaxation time disagrees with the Arrhenius description. In addition, the internal friction measurement at 1 Hz shows a mechanical loss peak that is of static hysteresis type. Therefore the viscous motion of domain walls in PZT is dominant in a certain frequency range of a few kHz. Dielectric loss as a function of temperature under frequencies from 1 to 10 kHz is modelled by using the dynamic equation for the viscous motion of domain walls. In the simulation, the dispersion of phase transition temperature inside the ceramics has been considered. The simulation results meet quite satisfactorily the experimental data. The two important parameters, viscous coefficient and pinning force constant, can be estimated.

Synthesis of mesoporous nanocrystalline Co3O4 via an easy and inexpensive method

In this paper, we report the synthesis of mesoporous nanocrystalline Co3O4 via a one-step, convenient and inexpensive method. The obtained Co3O4 powder samples were characterized by x-ray diffraction, N2 adsorption–desorption experiments and transmission electron microscopy. It is revealed that the molar ratio of the reactant and the calcination temperature had a significant influence on the morphology and the pore-sized distribution of the Co3O4 samples. A possible formation mechanism of mesoporous Co3O4 nanocrystalline is proposed.

Electronic structure and photocatalytic properties of In6WO12

In this paper, indium tungsten oxide In6WO12 was prepared by a solid-state reaction method. The sample that was obtained was characterized by x-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy and Brunauer–Emmett–Teller (BET) measurement. According to the diffuse reflectance spectra of the sample, the band gap is estimated to be 3.3 eV. The photocatalytic properties of the In6WO12 sample were evaluated by photo-decomposing acetaldehyde. The experimental results showed that the acetaldehyde could be mineralized to CO2 over In6WO12 under Xe lamp irradiation. The optimized crystal structure and calculated ground-state electronic structure of In6WO12 were also reported by using the standard CASTEP package.

The resistance degradation of (Ba0.5Sr0.5)TiO3 thin films

Abstract The leakage current and dielectric properties of (Ba0.5Sr0.5)TiO3(BST) thin films prepared by pulsed laser deposition (PLD) were investigated. It was found that leakage currents for positive bias voltage were higher than that for negative bias voltage, which was attributed to the lattice mismatch between bottom Pt electrode and BST thin film. The time-dependent breakdown process under positive voltage was observed, which was interpreted as the increase of the internal electric field in the film near the bottom electrode. However, the internal electric field can be decreased and eventually recovered by applying negative bias voltage. It was found that internal electric field near the interface can influence the capacitance of the BST thin film capacitor. An explanation for the thickness effect of BST thin films was given.