The Σ5(210)/ grain boundary (GB) of methyl-ammonium lead triiodide (MAPbI3) perovskite, one of the high-symmetry coincident site boundaries, is characterized by density functional theory. We searched for the lowest energy GB structure through ab-initio atomistic relaxation of symmetric twin boundaries with and without translational shifts relative to the GB plane. We confirmed that the symmetric Σ5(210)/ GB of MAPbI3 perovskite is the most stable among all the structures examined. The electronic density of states of the GB structure reveals no gap states. The electronic states of the valence-band maximum and conduction-band minimum are mainly p orbitals of I and Pb atoms, respectively.
Due to its excellent biocompatibility, hydroxyapatite is used as an implant material. Synthesis of highly dispersed hydroxyapatite nanoparticles is demanded because the properties of sintered hydroxyapatite scaffolds depend on the dispersibility of nanoparticles as raw material. We examined the effect of citric acid addition in hydroxyapatite slurry synthesized from Ca(NO3)2, NH4H2PO4 and tris-hydroxymethyl aminomethane (tris), while the citric acid is conventionally added in the solution from the beginning of apatite synthesis. Tris was used as base to precipitate hydroxyapatite, and immediately afterwards, citric acid was added to adjust the pH of the hydroxyapatite slurries. Citric acid was also selected as the dispersant and stabilizer for the hydroxyapatite slurries. The addition of citric acid to the slurry conferred a negative charge to the hydroxyapatite surface, which increased the absolute value of zeta potential of the particles. The zeta potential of particles in a pH 8.6 slurry was -24.6 mV, which prevented their agglomeration and sedimentation. Thus, the adsorption of citric acid effectively dispersed the hydroxyapatite particles. The hydrodynamic diameter of the particles decreased as the pH of the slurry decreased by the addition of citric acid.
Three powders with compositions close to 0.98(Na0.50K0.45Li0.05)NbO3−0.02Ca(Zr0.5Ti0.5)O3 (NKLN−CZT) were synthesized using a malic acid complex solution method, and three solid solutions were then fabricated using a conventional solid-state reaction technique. The optimal substitutional Ta content and Zr/Ti ratio for NKLN−CZT were examined by measuring the piezoelectric properties. Based on the results, a 0.98(Na0.50K0.45Li0.05)(Nb0.98Ta0.02)O3−0.02Ca(Zr0.4Ti0.6)O3 solid solution was fabricated to clarify the synergistic effect when the optimal values for both these parameters were used. The resulting material was found to exhibit the maximum longitudinal piezoelectric coefficient of 240 pC/N and radial electromechanical coupling factor of 41%. On the basis of these results and those for the average and local structure obtained using high-energy X-ray diffraction, this compound has potential as a high-Curie-temperature, high-performance, lead-free piezoelectric material.
Transition metal dichalcogenides (TMDCs) and related layered materials have attracted increased attention due to their intriguing chemical, physical, electrical and optical properties. Here, we investigated the influence of surface properties, which are their morphology and chemical composition, on the chemical vapor deposition (CVD) synthesis of a uniform molybdenum disulfide (MoS2) monolayer on support materials with several structures, such as flat, tubular, and porous materials. We found that, even under similar CVD conditions, the structure of the as-synthesized MoS2 layer differed significantly between sapphire and SiO2/Si substrates. Raman and photoluminescence (PL) measurements demonstrate that the surface chemical composition contributed to the self-assembly crystal growth of MoS2, affecting layer stacking. Moreover, the MoS2 layer synthesis by CVD on tubular and porous materials is also demonstrated. This work provides insights into the CVD synthesis of uniform MoS2 monolayers on several support materials with the advantages of one-pod, non-transferrable, and compatible with direct applications.
CuFeO2 is a prospective photocathode material for photoelectrochemical water-splitting with elemental strategic approaches point of view. In our previous study, we have demonstrated the direct fabrication of CuFeO2 films from an Fe substrate for enhancing adhesion strength of photocathode and current collector interface. We confirmed their photocatalytic response to visible light as photocathode; however, both their hydrogen overvoltage and corresponding current density were not enough as compared to theoretical efficiency. It is due to a lack of acceptor density in CuFeO2 film. In this paper, we studied the post-treatment effects to the CuFeO2/Fe photocathodes. Our systematic studies revealed that post-annealing and acid treatments provided the positive effects even on CuFeO2 films directly fabricated by hydrothermal method.