Synthesis, Characterization, and Applications of Water-Soluble Tantalum Carboxylate Precursors via a Flux Method

A novel, simple, and feasible route for synthesizing air-stable, water-soluble tantalum precursors has been developed using moisture-insensitive Ta₂O₅ as a starting source of the Ta element, based on the conventional basic flux method. Various analytical techniques have been used to characterize the formation mechanism, purity, and thermal decomposition features of these Ta precursors including tantalum oxalate, tantalum peroxo-tartarate, and tantalum peroxo-citrate. These Ta precursor solutions have a higher Ta ion purity over 99.0 wt% and a lone shelf life. Using home-made Ta precursors, photocatalyst powders of 1 mol% Ta-doped ZnO and ferroelectric films of SrBi₂Ta₂O₉ on Pt/TiO₂/SiO₂/Si substrates have been prepared by a modified polymerizable complex (PC) route. Ta-doped ZnO powders from polymeric precursors show hexagonal wurtzite structures with uniform smaller grain sizes of 25 nm and a larger specific surface area of 32 m²/g. Moreover, they exhibit excellent photocatalytical activity under visible light irradiation compared with pure ZnO powders. PC-derived SrBi₂Ta₂O₉ films also show comparable ferroelectric and dielectric properties with those from the metalorganic decomposition method. All these qualities indicate that water-soluble Ta precursors are potential and competitive candidates for photocatalyst and ferroelectric applications.     

The Antibacterial Activity of Ta-doped ZnO Nanoparticles

A novel photocatalyst of Ta-doped ZnO nanoparticles was prepared by a modified Pechini-type method. The antimicrobial study of Ta-doped ZnO nanoparticles on several bacteria of Gram-positive Bacillus subtilis (B. subtilis) and Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) were performed using a standard microbial method. The Ta-doping concentration effect on the minimum inhibitory concentration (MIC) of various bacteria under dark ambient has been evaluated. The photocatalytical inactivation of Ta-doped ZnO nanoparticles under visible light irradiation was examined. The MIC results indicate that the incorporation of Ta⁵⁺ ions into ZnO significantly improve the bacteriostasis effect of ZnO nanoparticles on E. coli, S. aureus, and B. subtilis in the absence of light. Compared to MIC results without light irradiation, Ta-doped ZnO and pure ZnO nanoparticles show much stronger bactericidal efficacy on P. aeruginosa, E. coli, and S. aureus under visible light illumination. The possible antimicrobial mechanisms in Ta-doped ZnO systems under visible light and dark conditions were also proposed. Ta-doped ZnO nanoparticles exhibit more effective bactericidal efficacy than pure ZnO in dark ambient, which can be attributed to the synergistic effect of enhanced surface bioactivity and increased electrostatic force due to the incorporation of Ta⁵⁺ ions into ZnO. Based on the antibacterial tests, 5 % Ta-doped ZnO is a more effective antimicrobial agent than pure ZnO.     

Excitation-induced tunable luminescent properties of polyhedral CaMoO4 microcrystallites

Journal of Materials Science: Materials in Electronics - Polyhedral CaMoO4 microcrystallites with excitation-induced tunable luminescent characteristics were successfully synthesized by a...     

Preparation and Characterization of Relaxor Ferroelectric 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 by a Polymerizable Complex Method

A modified polymerizable complex (PC) method for the preparation of the relaxor ferroelectric 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) ceramics has been developed using a novel water-soluble Nb precursor. The effects of Pb content and sintering temperature on the structure, morphology, composition, and electrical properties of PMN–PT powders and ceramics were investigated systematically. It was found that the modified PC method could effectively reduce the initial crystallization temperature of the perovskite phase to 500°C. For PMN–PT samples with 15% excess Pb content sintered at 600°C for 2 h, the 87% perovskite phase can be achieved, which is much higher than that in conventional solid-state reactions and other solution-based methods at the same temperature. On further increasing the sintering temperature to 1100°C, the perovskite phase content basically remains constant. This is attributed to the Pb-deficient pyrochlore phase formation. On increasing the sintering temperature to 1250°C, the dielectric constant and remnant polarization of PMN–PT ceramics significantly improved due to the larger grain sizes, enhanced density, and the decreasing pyrochlore phase. PMN–PT ceramics with a 98.5% content of the perovskite phase have been fabricated at 1250°C. It displays typical ferroelectric relaxor characteristics with a remnant polarization of 18 μC/cm², a coercive field of 9.6 kV/cm, a piezoelectric coefficient of d ₃₃=360 pC/N, and room-temperature and maximum dielectric constants of 3600 and 10 500 at 1 kHz, respectively.     

Abnormal phase transition in BiNbO4 powders prepared by a citrate method

Triclinic β-BiNbO₄ prepared below 750 °C and above 1040 °C (denoted as Low-β and High-β, respectively) and pure orthorhombic α-BiNbO₄ at 900 °C were successfully derived from a citrate method and the phase transition from β-BiNbO₄ to α-BiNbO₄ was first observed in BiNbO₄ powders. This phenomenon proves that the abnormal phase transition from β-BiNbO₄ to α-BiNbO₄ exists in BiNbO₄ powder system. The synthesis of Low-β powders can be attributed to the formation of the intermediate phase of Bi₅Nb₃O₁₅ by the citrate method. With increasing temperature, the Low-β phase gradually turns into α-BiNbO₄ due to the thermodynamically metastable state of Low-β. We also identified that the stress in pellet format can accelerate the phase transition from Low-β to α phase of BiNbO₄ in comparison with powder samples. It brings us new understanding of the BiNbO₄ system and also provides a simple way to obtain BiNbO₄ for microwave and photocatalytic applications.