Liang Bian

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.

DFT and two-dimensional correlation analysis methods for evaluating the Pu3+–Pu4+ electronic transition of plutonium-doped zircon

Understanding how plutonium (Pu) doping affects the crystalline zircon structure is very important for risk management. However, so far, there have been only a very limited number of reports of the quantitative simulation of the effects of the Pu charge and concentration on the phase transition. In this study, we used density functional theory (DFT), virtual crystal approximation (VCA), and two-dimensional correlation analysis (2D-CA) techniques to calculate the origins of the structural and electronic transitions of Zr1-cPucSiO4 over a wide range of Pu doping concentrations (c=0-10mol%). The calculations indicated that the low-angular-momentum Pu-fxy-shell electron excites an inner-shell O-2s(2) orbital to create an oxygen defect (VO-s) below c=2.8mol%. This oxygen defect then captures a low-angular-momentum Zr-5p(6)5s(2) electron to form an sp hybrid orbital, which exhibits a stable phase structure. When c>2.8mol%, each accumulated VO-p defect captures a high-angular-momentum Zr-4dz electron and two Si-pz electrons to create delocalized Si(4+)→Si(2+) charge disproportionation. Therefore, we suggest that the optimal amount of Pu cannot exceed 7.5mol% because of the formation of a mixture of ZrO8 polyhedral and SiO4 tetrahedral phases with the orientation (10-1). This study offers new perspective on the development of highly stable zircon-based solid solution materials.

Photovoltage response of (XZn)Fe2O4-BiFeO3 (X = Mg, Mn or Ni) interfaces for highly selective Cr3+, Cd2+, Co2+ and Pb2+ ions detection

High-photostability fluorescent (XZn)Fe2O4 (X=Mg, Mn or Ni) embedded in BiFeO3 spinel-perovskite nanocomposites were successfully fabricated via a novel bio-induced phase transfer method using shewanella oneidensis MR-1. These nanocomposites have the near-infrared fluorescence response (XZn or Fe)-O-O-(Bi) interfaces (785/832nm), and the (XZn)Fe2O4/BiFeO3 lattices with high/low potentials (572.15-808.77meV/206.43-548.1meV). Our results suggest that heavy metal ion (Cr3+, Cd2+, Co2+ and Pb2+) d↓ orbitals hybridize with the paired-spin X-Zn-Fe d↓-d↓-d↑↓ orbitals to decrease the average polarization angles (-29.78 to 44.71°), qualitatively enhancing the photovoltage response selective potentials (39.57-487.84meV). The fluorescent kinetic analysis shows that both first-order and second-order equilibrium adsorption isotherms are in line and meet the Langmuir and Freundlich modes. Highly selective fluorescence detection of Co2+, Cr3+ and Cd2+ can be achieved using Fe3O4-BiFeO3 (Langmuir mode), (MgZn)Fe2O4-BiFeO3 and (MnZn)Fe2O4-BiFeO3 (Freundlich mode), respectively. Where the corresponding max adsorption capacities (qmax) are 1.5-1.94, 35.65 and 43.7 multiple, respectively, being more competitive than that of other heavy metal ions. The present bio-synthesized method might be relevant for high-photostability fluorescent spinel-perovskite nanocomposites, for design of heavy metal ion sensors.

Computational Study of the Cation-Modified GSH Peptide Interactions With Perovskite-Type BFO-(111) Membranes Under Aqueous Conditions

We elucidated a number of facets regarding glutathione (GSH)-bismuth ferrite (BiFeO3, BFO) interactions and reactivity that have previously remained unexplored on a molecular level. In this approach, the cation-modified reduced GSH (or oxidised glutathione (GS·)) formed on the (111)-oriented BiFeO3 membrane (namely BFO-(111)) can serve as an efficient quencher, and the luminescence mechanism is explained in aqueous conditions. Notably, we suggest the use of Fe2+↓ ion as an electron donor and K+ ion as an electron acceptor to exert a “gluing” effect on the glutamic acid (Glu) and glycine (Gly) side chains, producing an exposed sulfhydryl (−SH) configuration. This method may enable the rational design of a convenient platform for biosensors.

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.

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.

Chemical stability of simulated waste forms Zr 1– x Nd x SiO 4– x/2 : Influence of temperature, pH and their combined effects

Abstract The chemical stability of simulated waste forms Zr 1– x Nd x SiO 4– x /2 was investigated using the static leach test (MCC-1) with lixiviants of three pH values (pH=4, 6.7 and 10) at three temperature points (40, 90 and 150 °C) for periods ranging from 1 to 42 d, and the influence of temperature, pH, as well as their combined effects were explored in detail. The results showed that all the normalized release rate of Nd firstly decreased with leaching time and closed to equilibrium after 14 d. As the temperature increased, the normalized release rate of Nd also increased, but it was no more than 3×10 –5 g/(m 2 ·d). And, the normalized release rate of Nd reached the highest values (∼5×10 –5 g/(m 2 ·d)) when pH=4, whilst the normalized release rate of Nd remained the lowest value (∼1×10 –5 g/(m 2 ·d)) near neutral environment (pH=6.7).

Synthesis of Nano-BiFeO3 by Low-heating Temperature Solid State Precursor Method: Using Different Types of Alkali

A new way to prepare BiFeO3 nano-powders by low-heating temperature solid state precursor method is presented in this paper. Room-temperature solid state reaction was adopted to prepare the precursors, which were further calcined in low-heating temperature at 500°C to synthesize nano-BiFeO3. The particle size of BiFeO3, ranging from 18 to 80 nanometers, can be effectively controlled by different alkali in raw materials. Owing to the quantum size effect, the optical band gaps and magnetic characteristics of BiFeO3 increased with the decreasing particle size.

Computational investigation on the new high energy density material of aluminum enriched 1, 1-diamino-2, 2-dinitroethylene

Aluminum enriched 1, 1-diamino-2, 2-dinitroethylene (Al-FOX-7) crystal, as a new high energy density material (HEDM), was designed and investigated using grand canonical monte carlo (GCMC), NVT+NPT-molecular dynamics (MD) and GGA-PBE-density functional theory (DFT) methods. The results show that, Al atoms break out H-bond of functional group of FOX-7 crystal, and form new Al-H and Al-O bonds. Their atomic content (x) influences the surface electronic states, friction sensitivities and cj detonation properties of Al-FOX-7 crystals. While x is 4 atoms, the crystal has the highest friction sensitivities and cj detonation temperatures, which are about 1.5 times to that of FOX-7 crystal.

Detection mechanism of perovskite BFO (1 1 1) membrane for FOX-7 and TATB gases: molecular-scale insight into sensing ultratrace explosives

Perovskite bismuth ferrite-BFO (1 1 1) membranes, as potential-sensitive electrochemical sensors, are investigated for the detection of high-energy-density materials by molecular dynamics (MD) and density functional theory (DFT) calculations. For the detection mechanism of the sensitive 1, 1-diamino-2, 2-dinitroethylene (FOX-7) gases, both a cation bridge and electrostatic models can be used to explain the STM signatures as 0.02–0.04 V (single) and 0.03~0.05 V (coverage) over a wide range (0–0.1 V) of bias voltages. For insensitive 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB) gases interacting with the surface of a BFO (1 1 1) membrane, the charge signature can be as high as 0.08 V (coverage: 0.06 V). Analysis indicates a significant difference from the detection mechanism observed for FOX-7 gases; that is, the molecularly intact bidentate bridge configuration with only – bonds binds to both Fe and Bi atoms. These differences are attributed so that the surface O2− of BFO will capture a part of the surface electron of the –NO2 group, creating a 2p-hole defect (h+) which annihilates a spinning upward (↑) Fe3+, forming a spinning downward (↓) Fe2+. The –NO2 electron decreases 0.35 e (single FOX-7; coverage FOX-7: 0.24 e) and 0.56 e (single TATB; coverage TATB: 0.06 e). Such a system could open up new ideas in the design and application of BFO-based sensors.