Bingcheng Luo

Orientation-dependent piezoelectric properties in lead-free epitaxial 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 thin films

Orientation-engineered 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on La0.7Sr0.3MnO3-coated SrTiO3 single-crystalline (001), (110), and (111) substrates by off-axis radio-frequency magnetron sputtering. X-ray diffraction confirmed a highly epitaxial growth of all the as-deposited films. It is believed the strong orientation dependence of ferroelectric and piezoelectric properties on the films is attributed to the relative alignment of crystallites and spontaneous polarization vector. The optimal ferroelectric response lies in the [001] direction, whereas a comparatively large effective piezoelectric coefficient d33,eff of 100.1 ± 5 pm/V was attained in [111] BZT-BCT thin film, suggesting its potential application for high-performance lead-free piezoelectric devices.

Positive colossal magnetoresistance effect in ZnO∕La0.7Sr0.3MnO3 heterostructure

In this letter, an oxide heterostructure has been fabricated by successively growing La0.7Sr0.3MnO3 and ZnO layers on a LaAlO3 (100) substrate using pulsed laser deposition. The ZnO∕La0.7Sr0.3MnO3 heterostructure exhibits good rectifying behavior and a positive colossal magnetoresistance (MR) effect over a temperature range of 77–280K. The maximum MR values are determined to be about 53.9% at H=0.5T and 36.4% at H=0.3T. A possible explanation is given in terms of the effect of magnetic fields on the depletion layer and the capture carriers effect at the interface.

Macroscopic liquid phase separation of Fe–Sn immiscible alloy investigated by both experiment and simulation

The macroscopic phase separation of undercooled liquid Fe50Sn50 immiscible alloy was investigated by both drop tube experiment and the modified Model H. Core-shell structures with two, three, and five layers were formed during experiment. The concentric shells comprised of Fe-rich phase and Sn-rich phase distribute periodically in the solidified droplet, and the Sn-rich phase is always located at the sample surface owing to its smaller surface tension. The simulated results of modified Model H reproduce core-shell structures with the same layers, which justifies the prediction of this model. If the fluidity parameter Cf and solute concentration ϕ satisfy the physical conditions of both Cf<1 and 0<ϕ<0.45 or Cf≥1, the phase separation morphology exhibits the double-layer core-shell structure, whereas the multilayer core-shell structure is expected to form under the conditions of both Cf<1 and 0.45≤ϕ<0.5. The forming ability of core-shell structure for various immiscible alloys can be predicted accordingly.

Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface

We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems.

Photoinduced phase transition and relaxation in bare SrTiO3 single crystals

The photoinduced insulator-metal phase transition and relaxation characteristics have been investigated in bare SrTiO3 single crystals. The photoinduced relaxation time constant after the irradiation shows an increase with increasing temperatures. The SrTiO3 single crystal has a cutoff wavelength and an absorption edge of spectrum at about 385 nm, which agrees well with the band gap. The photocurrent responsivity is 1.36 × 10−5 A/W at 300 nm wavelength. The relative change in resistance is more than above six orders at room temperature, possessing potential applications in ultraviolet sensitive and detecting devices.

Ultraviolet photovoltaic effect in BiFeO3/Nb-SrTiO3 heterostructure

We report on ultraviolet photovoltaic effects in a BiFeO3/Nb-doped SrTiO3 heterostructure prepared by a pulsed laser deposition method. The heterostructure exhibits rectifying behaviors in the temperature range from 80 K to 300 K. The photovoltage of heterostructure is about 0.33 V at T = 80 K when it is illuminated by a KrF excimer laser with a wavelength of 248 nm. The peak photovoltages decrease with increasing the temperature because of the accumulation of photogenerated carriers. Moreover, the peak photovoltages of heterostructure almost linearly increase with an increase of the power density of laser at T = 300 K. The results reveal some properties that may be useful for possible applications in multiferroic photoelectric devices.

The electric transport properties of Al-doped ZnO/BiFeO3/ITO glass heterostructure

BiFeO3 (BFO) and 4 wt. % Al-doped ZnO (ZAO) layers were grown on indium tin oxide (ITO) glass substrate using a pulsed laser deposition (PLD) method. I–V curves of the ZAO/BFO/ITO glass structure were investigated over the temperature range from 60 to 240 K. Analysis of the leakage current demonstrates that Poole–Frenkel emission is the dominant mechanism in our sample. The relations between resistance and temperature at positive and negative bias voltages are different, and the difference arises from the ferroelectric switching in BFO and the interfacial depletion layer between the semiconducting and the ferroelectric layers. Magnetoresistance (MR) effect is observed and the negative MR is related to the electron spin-dependent scattering and the interface resistance of the heterostructure.

Role of the defect in determining the properties of PbTi0.9Ni0.1O3 thin films

PbTiO3 with oxygen-vacancy-stabilized d8 ion substitution has attracted significant attention as a promising photo-ferroelectric material, but less effort to understand the effect of defect structures on its macroscopic properties limits further modification of the functionality via defect engineering. Herein, a comparable investigation of highly-(111) oriented PbTiO3 (PTO) and PbTi0.9Ni0.1O3 (PTN) thin films is reported to realize the critical role of defect structures on the evolution of electrical and photovoltaic properties. It is found that the PTO thin film shows the space-charge-limited-current mechanism, while the PTN thin film obeys the Poole–Frenkel emission mechanism. Also, the dielectric abnormal peak emerges in the PTN thin film. Notably, the ferroelectric polarization still keeps a large value but the band gap is lowered, and thus a significant increment of photovoltaic properties is achieved in the PTN thin film. These experimental results can be well explained if the formation of dopant-va...

Self-powered ultraviolet photovoltaic effects based on metal/SrTiO3 Schottky junctions

Self-powered ultraviolet photovoltaic effects have been investigated in metal/SrTiO3 Schottky junctions. The absorption edge of the SrTiO3 single crystal is about 389 nm. The peak photovoltage of the Pt/SrTiO3 junction is about 0.50 V at when it is illuminated by a KrF excimer laser with a wavelength of 248 nm. The peak photovoltages decrease with increasing the temperature due to the strong thermal fluctuation. Moreover, the peak photovoltages almost linearly increase with an increase in the power density of the laser at . The experimental results reveal it may be useful for self-powered ultraviolet detecting sensitive devices.

Photoconductivity of CaH2-reduced BaSnO3 thin films

Incorporation of foreign chemical elements in oxides can significantly alter their optoelectronic performances, and thus it is widely used to seek new transparent conductive oxides. Chemical-doping BaSnO3 systems, like La-doped BaSnO3, are of increasing interest with extremely high electrical mobility and excellent oxygen stability, exhibiting the potential application in next-generation all-perovskite optoelectronic devices. In this work, hydrogen was introduced into BaSnO3 through CaH2 reduction of BaSnO3 thin films, and the electrical properties, as well as the photo-response behavior, were investigated. Secondary ion mass spectroscopy demonstrated the uniform distribution of hydrogen within the BaSnO3 thin film. The addition of hydrogen greatly enhanced the conductivity of the BaSnO3 thin film, exhibiting a carrier concentration ∼8.04 × 1019 cm−3 and mobility ∼9.52 cm2 V−1 s−1 at 300 K, and thus resulted in a fast relaxation process in the transient photoconductivity, which was characterized by a double exponential function indicating two physical contributions.