Aimin Chang

Enhanced open voltage of BiFeO3 polycrystalline film by surface modification of organolead halide perovskite

Inorganic-organolead halide perovskite CH3NH3PbI3 modified BiFeO3 polycrystalline film has been established. The composite photoelectrode presents much larger open voltage and several magnitudes superior photoelectric conversion performance in comparison to the ordinary BiFeO3 polycrystalline film. The I-V curve shows that the short-circuit current (J(sc)) is 1.74 mA.cm(-2) and open-circuit voltage (V-oc) is 1.62 V, the devices photon to current efficiency is over 1%. The large open voltage and high photovoltaic efficiency is believed to attributed to the spontaneous polarization of composite perovskite induced by BiFeO3 lattice and modified reduced work function of the modified BiFeO3 surface. Our results clearly show that the present BiFeO3-CH3NH3PbI3 planar device is capable to generate a large voltage in macro scale under visible light, leading an approach to further applications on photodetectors and optoelectronic switch.

Electrical conductivity anomaly and X-ray photoelectron spectroscopy investigation of YCr1−xMnxO3 negative temperature coefficient ceramics

Electrical conductivity anomaly of perovskite-type YCr1−xMnxO3 negative temperature coefficient (NTC) ceramics produced by spark plasma sintering (SPS) has been investigated by using defect chemistry theory combination with X-ray photoelectron spectroscopy (XPS) analysis. From the results of the lnρ-1/T curves and the XPS analysis, it can be considered that YCr1−xMnxO3 ceramics exhibit the hopping conductivity. The major carriers in YCrO3 are holes, which are compensated by the oxygen vacancies produced due to the introduction of Mn ions. The Mn4+ ion contents increase monotonically in the range of 0.2 ≤ x ≤ 0.5. The resistivity increases at first and then decreases with increasing Mn contents, which has the same varying tendency with activation energy. The electrical conductivity anomaly appearing in these ceramics may be due to the variation of Cr4+ and Mn4+ ions concentration as Mn content changes.

Temperature-induced work function changes in Mn1.56Co0.96Ni0.48O4 thin films

The variations of work functions in Mn1.56Co0.96Ni0.48O4 (MCN) thin films are investigated in the temperature range from 30 to 80 °C. The high resolution images of the contact potential difference (CPD) of MCN thin films were obtained through Kelvin probe force microscopy (KPFM) and the correlations between the work functions and temperatures were demonstrated through the imaginary part of the dielectric functions. The complex dielectric spectra are temperature dependent while their intensities have the inverse trend according to the work functions. The phenomenon can be interpreted by different chemical states that relate to the Mn3+ state.

Preparation and thermal-sensitive characteristic of copper doped n-type silicon material

Copper doped n-type single-crystal silicon materials are prepared by a high temperature diffusion process. The electrical and thermal-sensitive characteristic of materials is investigated under different experimental conditions. The results show that the maximum resistivity of 46.2 Ω ·cm is obtained when the sample is treated at 1200 ℃ for 2 h with the surface concentration of the copper dopant source being 1.83 × 10 -7 mol/cm 2 . The copper doped n-type silicon material presents a negative temperature-sensitive characteristic and the B values are about 3010-4130 K.

Characterization and electrical conductivity of La1−xSrxCrO3 NTC ceramics

The La1−xSrxCrO3 (x = 0–0.1) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid state reaction method. X-ray diffraction (XRD) analysis has revealed that the as-sintered ceramics crystallize in a single perovskite structure. Scanning Electron Microscope (SEM) images show that the doped Sr2+ contributes to in the decrease in porosity. X-ray photoelectron spectroscopy (XPS) analysis indicates the existence of Cr3+ and Cr6+ ions on lattice sites, which result in hopping conduction. The presence of the Cr6+ is one of the key factors that affect the electrical conductivity of La1−xSrxCrO3. Resistance–temperature characteristics were studied in the range of −80 to 10 °C for the ceramic samples, the electrical characterizations show that the electrical resistivity and material constant B decrease with the increase of the strontium content.

Formation of Mn‐Co‐Ni‐O Nanoceramic Microspheres Using In Situ Ink‐Jet Printing: Sintering Process Effect on the Microstructure and Electrical Properties

Mn-Co-Ni-O nanoceramic microspheres with high density, uniformity, and size tunability are successfully fabricated using in situ ink-jet printing and two step sintering (TSS) techniques. The microspheres, synthesized by an effective and facile reverse microemulsion method, consist of uncalcined Mn-Co-Ni-O nanocrystallines that show a well formed single tetragonal spinel phase and an average particle size distribution of ≈20 nm. The sintering behavior, microstructure, and electrical properties of the Mn-Co-Ni-O nanoceramic microspheres are systematically investigated and characterized. The results indicate that the sintered Mn-Co-Ni-O nanoceramic microspheres show high density and improved electrical properties. The highest R25 , B25/50 , Ea , and α25 values achieved at sintering temperature of 1150 °C are 4846.7 KΩ, 4320 K, 0.401 eV, and -5.24% K-1 , respectively for these Mn-Co-Ni-O nanoceramic microspheres. Furthermore, the formation mechanism of uncalcined Mn-Co-Ni-O nanocrystallines and an analysis of the TSS procedure of the nanoceramic microspheres are discussed.

Calcium manganate: A promising candidate as buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems

We have systematically studied the feasibility of CaMnO3 thin film, an n-type perovskite, to be utilized as the buffer layer for hybrid halide perovskite photovoltaic-thermoelectric device. Locations of the conduction band and the valence band, spontaneous polarization performance, and optical properties were investigated. Results indicate the energy band of CaMnO3 can match up well with that of CH3NH3PbI3 on separating electron-hole pairs. In addition, the consistent polarization angle helps enlarge the open circuit voltage of the composite system. Besides, CaMnO3 film shows large absorption coefficient and low extinction coefficient under visible irradiation, demonstrating high carrier concentration, which is beneficial to the current density. More importantly, benign thermoelectric properties enable CaMnO3 film to assimilate phonon vibration from CH3NH3PbI3. All the above features lead to a bright future of CaMnO3 film, which can be a promising candidate as a buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems.

A Comparison Study of Sinterability and Electrical Properties for Microwave and Conventional Sintered Mn0.43Ni0.9CuFe0.67O4 Ceramics

In this paper, a quaternary system of Mn0.43Ni0.9CuFe0.67O4 negative temperature coefficient (NTC) thermistor ceramic prepared by solid/solid reaction was sintered by microwave and conventional method, respectively. To characterize the sinterability of the samples, the densification parameter, porosity and grain size distribution of the bulk were determined. The crystal structure, phase compositions, morphology and impedance of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and impedance analysis. The experimental results confirmed that the sinterability and electrical properties of ceramics were homogenously improved by microwave sintering.

QtUCP—A program for determining unit-cell parameters in electron diffraction experiments using double-tilt and rotation-tilt holders

A computer program, QtUCP, has been developed based on several well-established algorithms using GCC 4.0 and Qt 4.0 (Open Source Edition) under Debian GNU/Linux 4.0r0. It can determine the unit-cell parameters from an electron diffraction tilt series obtained from both double-tilt and rotation-tilt holders. In this approach, two or more primitive cells of the reciprocal lattice are determined from experimental data, in the meantime, the measurement errors of the tilt angles are checked and minimized. Subsequently, the derived primitive cells are converted into the reduced form and then transformed into the reduced direct primitive cell. Finally all the patterns are indexed and the least-squares refinement is employed to obtain the optimized results of the lattice parameters. Finally, two examples are given to show the application of the program, one is based on the experiment, the other is from the simulation.

Strong optical absorption of LaMn0.6Al0.4O3 thin films in the mid-infrared atmospheric window

Strong light absorption in the mid-infrared atmosphere window (3–5 μm) was reported for a complete (100)-oriented LaMn0.6Al0.4O3 thin film. It is attributed to Al-doping induced electron transitions from the polar center of a [MnO610−]JT pseudo-Jahn–Teller electron cluster to a [MnO68−]JT pseudo-Jahn–Teller hole cluster and strain intensification.