Chemical System Engineering

An investigation was carried out on the effects of using a flux during the fabrication of SrNbO 2 N particles on the photoelectrochemical (PEC) properties of CoPi/SrNbO 2 N/Nb/Ti photoanodes prepared by a particle transfer method. The type of flux and the synthesis conditions were found to affect the morphology and crystallinity of oxide precursors and subsequently nitrided SrNbO 2 N. By a suitable choice of flux synthesis conditions, the PEC performance of the photoanodes could be improved. Oxide precursors treated with a NaI flux were solid solutions of NaNbO 3 and Sr 4 Nb 2 O 9 , and had a perovskite-type structure. When the precursors were first pre-calcined, larger secondary SrNbO 2 N particles with a higher degree of crystallinity were obtained. As a result, a photocurrent density of 1.5 mA cm À2 at 1.23 V RHE was achieved under simulated sunlight (AM 1.5G) in an alkaline solution (pH 13).

Ferroelectric properties of epitaxially grown Bi 2 SiO 5 films were investigated. Bi 2 SiO 5 films were deposited by pulsed laser deposition on SrTiO 3 substrates with different orientations. Films with various orientations such as (100), (411), and (210)/(201) were successfully grown on SrTiO 3 substrates with (100)-, (110)-, and (111)-orientations, respectively. Furthermore, Bi 2 SiO 5 films deposited on (111)SrTiO 3 substrates were highly (201)-oriented, indicating the selective growth of c-related facet due to the better lattice matching. Although Bi 2 SiO 5 films do not contain perovskite blocks in its structure, film orientations of Bi 2 SiO 5 were able to be controlled in a similar manner in the case of bismuth layered structure ferroelectrics with perovskite blocks. A (411)-oriented Bi 2 SiO 5 film exhibited a clear ferroelectric feature and showed a saturation polarization of about 7.8 μC cm −2. Our findings show that epitaxial Bi 2 SiO 5 thin films with a layered structure without perovskite blocks are a promising candidate for ferroelectric devices.

TiO 3 0.9BaTiO 3 thin films were deposited by pulsed laser deposition as a candidate of lead-free thin films with a positive temperature coefficient of resistance for micro-thermistor applications in microelectro mechanical system devices. (001)-oriented epitaxial tetragonal films with a unity (Bi + Na + Ba)/Ti ratio were grown at 675°C under a total pressure of 50 mTorr. The obtained films showed improved insulating properties and clear ferroelectricity. The Curie temperature was estimated to be 200°C by the high-temperature X-ray diffraction measurement, which was almost the same as the reported value for the ceramic.

Hiromu Kumagai opened a discussion of the paper by Akihiko Kudo: Do you have any strategy to suppress CO evolution from RGO which was used in the Zscheme system, such as substitution of some compounds? In water splitting using similar Z-scheme conguration with RGO, does same oxidation of RGO to form CO progress? Akihiko Kudo answered: In the present system, we used TiO 2 that has strong oxidation power due to the deep valence band. That is the reason why a part of CO forms by oxidation of RGO. If you employ an O 2-evolving photocatalyst with a shallower valence band such as BiVO 4 , the undesirable oxidation is suppressed. Hiromu Kumagai asked: Why do similar Z-scheme systems show different behavior for RGO oxidation between using in water splitting and in CO 2 reduction? Akihiko Kudo answered: In the previous literature for water splitting, 1 H 2 and O 2 simultaneously evolved in a stoichiometric amount. In that case, the Pt cocatalyst was loaded on CuGaS 2. In contrast, when the Pt cocatalyst is not loaded in the present CO 2 reduction, the ratio signicantly deviated from 2 : 1 for water splitting under Ar, and RGO oxidation also proceeded. These results suggest that the Pt cocatalyst works not only for H 2 evolution on CuGaS 2 , and probably for hole transfer from CuGaS 2 to RGO, but also suppression of the RGO oxidation in water splitting.

Ferroelectric thin films are important because of their great potential for use in various electric devices such as ferroelectric random-access memory. It was expected that Bi 2 SiO 5 , a Si-containing ferroelectric material, would show improved ferroelectricity by targeting a film with the (001)-orientation (polaraxis) on the substrate. Although there was a narrow process window for the deposition of the (010)/ (001)-oriented Bi 2 SiO 5 thin film, it was successfully prepared on a (101)-oriented TiO 2 single substrate using the pulsed layer deposition technique. The optimum film deposition conditions and film thickness were found, and in this material, the volume fraction of the (001)-oriented domain reached about 70%. By controlling film orientation to the polar axis, the remanent polarization value of this film was 4.8 μC cm −2 , which is the highest value among reported Bi 2 SiO 5. Ferroelectric materials are used in various applications such as ferroelectric random-access memory, actuators, and strain sensors 1-4. Ferroelectrics exhibit a high dielectric constant (ε r), stemming from a sharp increase in ε r caused by a ferroelectric-dielectric phase transition. Considering the relevance of ferroelectrics to Si-based industries, it is worth investigating ferroelectrics that contain silicon. Despite this, to date, both the number of papers on Si-containing ferroelectric materials and the variety within this class of materials is very limited. Among the Si-containing ferroelectrics, bismuth silicate (Bi 2 SiO 5 , denoted as BSO) is one promising example 5,6. BSO has a crystal structure analogous to that of Aurivillius-type structures, such as Bi 2 VO 5.5 (BVO) and Bi 2 WO 6 (BWO), which are members of the famous ferroelectric family of bismuth layered-structure ferroelectrics (BLSFs). Although BLSFs have a layered perovskite-type structure, in BSO the perovskite-type blocks are replaced by SiO 4 chains. It was reported that this SiO 4 chain plays a major role in ferroelectricity and was assumed to exhibit spontaneous polarization of 23.5 μC cm-2 along the c-axis of BSO 7. In addition, BSO has recently received attention as a high-dielectric-constant material 8-10. Ferroelectric thin films, especially epitaxial films, have the advantage that their ferroelectric and dielectric properties can be controlled, in contrast to the bulk form. This is possible since these properties are greatly affected by the orientation of the film, owing to the asymmetric structure of ferroelectric materials. Among the BLSFs, SrBi 2 Ta 2 O 9 (SBT) and Bi 4 Ti 3 O 12 (BIT) epitaxial films have been extensively investigated; these studies have revealed that they exhibit different electrical properties depending on their orientation 11-13. For these compounds, the film orientation can be controlled by choosing suitable substrates with the correct orientations. Recently, it was reported that the film orientation of BSO can also be controlled using SrTiO 3 (STO) substrates with various orientations 14. The crystal growth of BSO on STO was similar to that of BLSFs on STO substrates because the lattice constants of BSO are close to those of BLSFs, as shown in Table 1. Furthermore, it has been claimed that epitaxial growth is mainly caused by the fluorite-type layers instead of the perovskite-type layers in BLSFs or silicate chains in BSO 15 .

We have developed the potassium salt of a new anionic spiropyran, 1¤,3¤,3¤-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2¤-indoline]-5¤-sulfonate (1 ¹ ), whose crystal structure was revealed by single-crystal X-ray diffraction analysis. The photochromism of 1¢K was demonstrated at room temperature in the KBr-diluted state, as well as in solution. The protonated spiropyran 1H shows a negative photochromism.

—This short paper reviews the equations of state and their application to phase equilibrium modeling. The strengths, weaknesses and applicability of these equations will be assessed. Our intention is to test the applicability of the Peng Robinson equation of state in the computation of thermodynamic interactions of volatile organic compounds and biodiesel. Thermodynamic models are very useful in phase equilibrium prediction as measurements are costly and time consuming.

Coronavirus disease 2019 (COVID-19) has spread throughout the world. The prediction of the number of cases has become essential to governments’ ability to define policies and take countermeasures in advance. The numbers of cases have been estimated using compartment models of infectious diseases such as the susceptible-infected-removed (SIR) model and its derived models. However, the required use of hypothetical future values for parameters, such as the effective reproduction number or infection rate, increases the uncertainty of the prediction results. Here, we describe our model for forecasting future COVID-19 cases based on observed data by considering the time delay (tdelay). We used machine learning to estimate the future infection rate based on real-time mobility, temperature, and relative humidity. We then used this calculation with the susceptible-exposed-infectious-removed (SEIR) model to forecast future cases with less uncertainty. The results suggest that changes in mobil...

The effect of sulfization temperature on Ga through film uniformity in a 2-reaction H2Se/H2S precursor process for Cu(lnGa)(SeS)2 was studied. CUo.8Gao.2/ln bi-Iayer precursors were prepared by sputter deposition. The precursors were then partially selenized at 450°C, followed by sulfization at temperatures ranging from 450 to 550°C. The observed threshold temperature for Ga homogenization during sulfization was-500°C. It is speculated that this threshold temperature possibly derives from a solid-+liquid phase transition at 485°C on the Ga-rich edge ofthe y1-CU9Ga4 phase region.

For Cu(In,Ga)Se 2 films made by the selenization of metallic precursors, Ga accumulation near the back contact prevents the achievement of high-voltage solar cells. In this work, selenization of mixed metal/ metal-selenide precursors has been evaluated with respect to the composition distribution in the Cu(In,Ga)Se 2 film and device performance. Four types of precursors consisting of electrodeposited and evaporated Cu-Se/Ga/In and (In,Ga)-Se/Cu were reacted in hydrogen selenide at 450 1C for 5, 15, and 90 min with metallic Cu 0.8 Ga 0.2 /In precursors as a control. Ga accumulation near the back contact in the selenized films was generally observed except for one precursor with a Cu-Se/Ga/In structure and excess Se in the Cu-Se layer, which had the maximum Ga concentration in the middle of the film. Enhanced Ga incorporation into the Cu(In,Ga)Se 2 is shown by X-ray diffraction for the precursors made from electrochemically deposited Cu-Se and changes in the bandgap were observed in the device behaviors.

Certified efficiency of 22.3% has been achieved for Cu(In,Ga)(Se,S) 2 solar cell. Compared to our previous record cell with 20.9% efficiency, the major breakthrough is due to the increased V oc , benefited from potassium treatment. A lower reverse saturation current and a longer carrier collection length deduced from electron-beam induced current indicate that the degree of carrier recombination at the heterojunction and depletion region for the 22.3% cell is lower. Further characterizations (capacitance-voltage profiling, temperature-dependent V oc , Suns-V oc) and analysis indicate that the recombination coefficients at all regions were reduced, especially for the interface and depletion regions. Device simulation was performed assuming varying defect densities to model the current-voltage curve for the 22.3% cell. The best model was also used to estimate the achievable V oc if defect densities were further reduced. Furthermore, by using higher bandgap Cd-free buffer layers, a higher J sc was achieved which gives an in-house solar cell efficiency of 22.8%. Recombination analysis on the 22.8% cell indicates that the interface recombination is further reduced, but the recombination coefficients at the depletion region was higher, pointing out that further improvement on the depletion region recombination could help to achieve a higher V oc and therefore an efficiency beyond 23%.

Record efficiency of 22.3% has been achieved for Cu(In,Ga)(Se,S) 2 solar cell. Compared to our previous champion cell with 20.9% efficiency, the major breakthrough is due to the increased open-circuit voltage (V OC), benefited from the post-deposition treatment using potassium (K) source. Further characterizations (CV, V OC-T, Suns-V OC) indicate that the recombination rates at the interface and depletion region were reduced significantly. This is supported by the EBIC images which show a prolonged carrier collection length away from the p-n interface. Based on the results, device simulation suggests that further reduction of surface defect density could enhance the V OC towards 760 mV.