Plug and Play Electrodeposition Cell: A Case Study of Bismuth Ferrite Thin Films for Photoelectrochemical Water Splitting

In the present study, we designed and fabricated cost-effective miniaturized versatile electrochemical deposition cell, which is found to be at par performance as compared with conventional electrodeposition techniques. A case study is being undertaken for the electrodeposition of varied thickness of bismuth ferrite (BiFeO3) films on FTO glass substrates. X-ray diffraction (XRD) patterns confirms the structural perovskite phase of BiFeO3 (BFO). UV-Visible absorption spectra and Tauc plot of BFO estimates the direct band gap which lies between 1.9 to 2.1 eV. The properties of bismuth ferrite crystal system such as electronic band structure and density of states (DOS) are investigated theoretically. Photoelectrochemical (PEC) water splitting application is carried out to investigate the best performance of BFO films of varied thickness. The best performer (BFO15) working electrode yields a photocurrent density of ~ 35 µA/cm2 at 0.2 V vs RHE under visible LED (light intensity of 100mW/cm2) in neutral 0.5 M Na2SO4 electrolyte. Incident photon to current conversion (IPCE) measurements, electrochemical impedance spectroscopy (EIS) and Mott-Schottky characteristics confirms the best performance of BFO15 photocathode film.

Measurement of polarization effects in dual-phase ceria-based oxygen permeation membranes using Kelvin probe force microscopy

In this study, a dual phase composite (CSO-FC2O) consisting of 60 vol % Ce0.8Sm0.2O1.9 as oxygen-conductive phase and 40 vol % FeCo2O4 as electron-conductive phase was synthesized. TEM measurements showed a relatively pure dual-phase material with only minor amounts of a tertiary (Sm,Ce)(Fe,Co)O3 perovskite phase and isolated residues of a rock salt phase at the grain boundaries. The obtained material was used as a model to demonstrate that a combination of polarization relaxation measurements and Kelvin probe force microscopy (KPFM)-based mapping of the Volta potential before and after the end of polarization can be used to determine the chemical diffusion coefficient of the ceria component of the composite. The KPFM measurements were performed at room temperature and show diffusion coefficients in the range of 3 × 10−13 cm2·s−1, which is comparable to values measured for single-phase Gd-doped ceria thin films using the same method.

Exploring the Spatial Control of Topotactic Phase Transitions Using Vertically Oriented Epitaxial Interfaces

Engineering oxygen vacancy formation and distribution is a powerful route for controlling the oxygen sublattice evolution that affects diverse functional behavior. The controlling of the oxygen vacancy formation process is particularly important for inducing topotactic phase transitions that occur by transformation of the oxygen sublattice. Here we demonstrate an epitaxial nanocomposite approach for exploring the spatial control of topotactic phase transition from a pristine perovskite phase to an oxygen vacancy-ordered brownmillerite (BM) phase in a model oxide La0.7Sr0.3MnO3 (LSMO). Incorporating a minority phase NiO in LSMO films creates ultrahigh density of vertically aligned epitaxial interfaces that strongly influence the oxygen vacancy formation and distribution in LSMO. Combined structural characterizations reveal strong interactions between NiO and LSMO across the epitaxial interfaces leading to a topotactic phase transition in LSMO accompanied by significant morphology evolution in NiO. Using the NiO nominal ratio as a single control parameter, we obtain intermediate topotactic nanostructures with distinct distribution of the transformed LSMO-BM phase, which enables systematic tuning of magnetic and electrical transport properties. The use of self-assembled heterostructure interfaces by the epitaxial nanocomposite platform enables more versatile design of topotactic phase structures and correlated functionalities that are sensitive to oxygen vacancies.

Simulation of the photonic nanojet effect for Raman scattering enhancement in the diagnostics of oxide films

In this paper, by means of numerical simulations in the COMSOL Multiphysics software it’s demonstrated that Raman scattering enhancement can be achieved for the diagnosis of metal oxide films using spherical particles made of barium titanate with a 10-micron diameter sphere. The formation of photonic nanojet in the sphere/film/substrate system at different radiation wavelengths and microsphere refractive index, film, and substrate was studied. The optimal interval of the particle refractive index is n≈1.8-2 was determined, at which the gain occurs directly at the particle/film interface. It is shown that for the UV wavelength range of wavelengths and film thicknesses from 50 to 200 nm, the gain is maximum. For ZnO and PZT films in the perovskite phase, sitall and quartz are preferred as the substrate material, while for PZT in the pyrochlore phase, sapphire is preferred.

Screen Printed Copper and Tantalum Modified Potassium Sodium Niobate Thick Films on Platinized Alumina Substrates

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d33 coefficient of 64 pm/V and an effective thickness coupling coefficient kt of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.

Temperature-Dependent Crystallization Mechanisms of Methylammonium Lead Iodide Perovskite From Different Solvents

Hybrid perovskites are a novel type of semiconductors that show great potential for solution-processed optoelectronic devices. For all applications, the device performance is determined by the quality of the solution-processed perovskite thin films. During solution processing, the interaction of solvent with precursor molecules often leads to the formation of solvate intermediate phases that may diverge the crystallization pathway from simple solvent evaporation to a multi-step formation process. We here investigate the crystallization of methylammonium lead iodide (MAPbI3) from a range of commonly utilized solvents, namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and gamma-butyrolactone (GBL) at different temperatures ranging from 40°C to >100°C by in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. For all solvents but GBL, we clearly observe the formation of solvate-intermediate phases at moderate processing temperatures. With increasing temperatures, an increasing fraction of the MAPbI3 perovskite phase is observed to form directly. From the temperature-dependence of the phase-formation and phase-decomposition rates, the activation energy to form the MAPbI3 perovskite phase from the solvate-phases are determined as a quantitative metric for the binding strength of the solvent within the solvate-intermediate phases and we observe a trend of DMSO > DMF > NMP > GBL. These results enable prediction of processing temperatures at which solvent molecules can be effectively removed.

VOC and CO Removals by Perovskite Type Nanocatalysts Supported on Commercial Substrates

In this research, it was tried to choose a kind of perovskite catalyst with optimized formulation La0.8Sr0.2Co0.66Fe0.34O3 to remove air pollutants. This perovskite catalyst stabilized on the various supports such as alumina and ZSM-5 with the sol-gel synthesis technique and ceramic monolith by dip-coating method. Four different catalysts by variable weight percentage including PE-Al 10%, PE-Al 20%, PE-Al 30%, and PE-Al 40% were prepared by sol-gel synthesis technique. In this work, the XRD technique was used to confirm the formation of perovskite catalysts’ crystalline phases on the supports. As a result, XRD patterns revealed the formation of the perovskite phase onto the alumina and zeolite supports. Activity tests of these four catalysts were examined in the catalytic oxidation of Toluene and CO using an experimental setup consisting of a tubular flow reactor at the temperature 280-400°C and 100-400°C for the toluene and CO removal systems, respectively. According to the results of the catalysts’ activity test, the alumina supported with 40% w/w perovskite catalyst showed the best performance, and its activity was similar to the activity of the bulk catalyst (over 95% conversion of toluene at about 290°C). For the coated catalysts on a ceramic monolith, the complete removal of carbon monoxide at 50°C was lower than the powdered form. Results from the activity test in a toluene removal system that show coating of the bulk and supported catalysts on ceramic monolith; have an essential impact on the activity test of these catalysts.