Phase Evolution and Optical Response of TiO2 Nanoparticle Films Induced by Controlled Thermal Annealing

A ZnO nanorods (NRs)/TiO2 nanoparticles (NPs) film has been prepared by electrochemical deposition of ZnO NRs growth on P25 TiO2 NPs film surfaces. It was found that ZnO NRs/TiO2 NPs could significantly improve the efficiency of dye-sensitized solar cells owing to its relatively enhanced light-scattering capability and efficient charge transport efficiency. The overall energy-conversion efficiency (η) of 3.48 % was achieved by the formation of ZnO NRs/TiO2 NPs film, which is 33 % higher than that formed by TiO2 NPs alone (η = 2.62 %). The charge recombination behavior of cells was investigated by electrochemical impedance spectra, and the results showed that ZnO NRs/TiO2 NPs film has the longer electron lifetime than TiO2 NPs alone, which could facilitate the reduction of recombination processes and thus would promote the photocatalysis and solar cell performance.

We aimed to prepare metal oxide materials with the optimal surface charge by preparing mixed films of non-modified metal oxide nanoparticles (NPs) with dissimilar isoelectric points (iep). The purpose of preparing such surfaces was to expand the use of metal oxide materials in environments where the solution pH cannot be changed. Langmuir films of SiO2 (iep: pH 2-3) and TiO2 (iep: pH 5-6.6) NPs were first prepared at air-100 mM NaCl aqueous interfaces. This subphase allowed the formation of stable films of the NPs without the need to modify the NPs with surface-active chemicals, whose presence may detrimentally change the properties of the films. The Langmuir films were then transferred and sintered to silicon wafers and their physical properties were characterized using atomic force microscopy (AFM). The AFM images showed that the films were composed of NP aggregates. The average size of the aggregates decreased, and the uniformity of the aggregate sizes and their inter-aggregate spacing increased with the addition of SiO2 NPs to the film of TiO2 NPs. These changes were explained by an increased electrostatic and steric repulsion between the aggregates formed at the air-100 mM NaCl interface due to the adsorption of negatively charged SiO2 NPs to the slightly positively charged TiO2 aggregates. The force-distance curves measured between a SiO2 probe and the sintered films of SiO2 and/or TiO2 NPs in a 1.0 mM NaCl solution adjusted to pH 4 showed that the magnitude of the repulsive force decreased with an increased number of TiO2 NPs in the film. This force change indicated that the surface charge changed when different types of NPs were mixed. These results indicate that mixing different NP types in a Langmuir film at an air-aqueous interface can help change the physical properties of the transferred film.

Phase evolution, microstructure and magnetic properties of bulk α-Fe/Nd2Fe14B nanocomposite magnets prepared by severe plastic deformation and thermal annealing

Unraveling the Impact of Halide Mixing on Crystallization and Phase Evolution in CsPbX3 Perovskite Solar Cells

Effect of B content on the magnetic properties, phase evolution, magnetic after effect, and the activation energy (Ea) for the melt-spun [(Fe0.7Co0.3)0.725Pt0.275]100−xBx (x=14–18) ribbons has been investigated. Sufficient amount of boron addition effectively decreases the activation energy of ordering transformation, and also refines the grain size of the studied ribbons after thermal annealing, resulting in the improvement of Hic from 3.4 kOe for x=14 to 6.2 kOe for x=18. The highest permanent magnetic properties of Br=10.1 kG, Hic=5.4 kOe, and (BH)max=15.7 MGOe can be achieved in [(Fe0.7Co0.3)0.725Pt0.275]85B15 ribbons. Meanwhile, the magnetic after effect study evidences that the activation volume is reduced with the increase in B content from V=41.33×10−19 cm3 for x=14 to V=21.71×10−19 cm3 for x=18, arisen from the lower volume fraction of magnetically soft phases and the stronger exchange-coupling effect between magnetic grains.

TiO2 nanoparticle was synthesized by the flame method using a metal organic precursor of titanium tetraisopropoxide (TTIP, Ti(OC3H7)4), which was controlled by varying the ratio and flow rate of gas mixtures consisting of oxygen (oxidizer), methane (fuel) and nitrogen (carrier gas). The morphology and the size distribution of nanoparticles were observed with TEM and FESEM, and the phase evolution was analyzed by XRD measurement using a monochromator. The crystalline phases of TiO2 nanoparticle depended strongly on the temperature distribution in the flame, whereas the morphology was not sensitive. During the flame synthesis of TiO2 nanoparticle, anatase TiO2 nanoparticle was predominantly synthesized at the high flame temperature and rapid flame cooling condition. The low flame temperature and long flame length enabled to form almost rutile TiO2 nanoparticle (>95%). The anatase nanoparticle was formed by a homogeneous nucleation and has finally kept the anatase phase without the phase transformation any more in the flame. However, the rutile TiO2 nanoparticle was not formed directly and homogeneously in flame, and was manufactured by the phase transformation such as amorphousanataserutile. It was proved that the rutile phase was nucleated heterogeneously from the amorphous or anatase particles.

External electric and magnetic fields enhanced photocatalytic efficiency of TiO2 nanoparticulate films prepared by sparking process

The properties of a material change remarkably as a result of the scaling dimensions. The Langmuir-Blodgett (LB) film deposition technique is known to offer precise control over the film thickness and the interparticle separation. To form a well-ordered LB film, it is essential to form a stable Langmuir film at the air-water interface. Here, we report our studies on ultrathin films of TiO2 nanoparticles at air-water and air-solid interfaces. The Langmuir film of TiO2 nanoparticles at the air-water interface was found to be very stable, and it exhibits loose-packing and close-packing phases. The LB films were transferred onto solid substrates for characterization and application. The surface morphology of the LB film was obtained by a field emission scanning electron microscope. The optical and electronic properties of the LB films of TiO2 nanoparticles were studied using UV-vis spectroscopy and current-voltage measurements, respectively. The LB film of TiO2 nanoparticles was employed for ethanol gas sensing, and the sensing performance was compared to that of bulk material. Because of the enormous gain in the surface to volume ratio and the increase in crystalline defect density in the ultrathin LB film of TiO2 nanoparticles, the LB film is found to be a potential functional layer for ethanol sensing as compared to the bulk material.

Observation of Significant enhancement in the efficiency of a DSSC by InN nanoparticles over TiO2-nanoparticle films

The properties of amorphous alloys are significantly influenced by structural relaxation and partial/full crystallization induced by thermal annealing of the alloy. In this paper, the phase evolution and mechanical behavior of laser‐patterned FeBSi amorphous alloys are reported. The laser patterning was employed to cause localized thermal effects on the surface of amorphous ribbons. The laser irradiation with a lower fluence (12 J · cm−2) caused significant embrittlement of the alloy due to the structural relaxation. The partial crystallization of an amorphous alloy into α‐Fe(Si) was also observed with laser irradiation using higher laser fluences (15 and 17 J · cm−2). The embrittlement effect due to laser‐irradiation‐induced crystallization was more severe than that due to structural relaxation.

The effect of stacking patterns and annealing conditions on phase evolution by solid-state reactions of thin multilayered Pt/Mn/Sb films

The effect of substrate heating on phase evolution and texture development by solid-state reaction of thin multilayered Pt/Mn/Sb films

Solid-state amorphization was achieved in the Ni48Nb52 multilayers upon thermal annealing by gradually raising the temperature from 250 to 400 °C and staying at 400 °C for 2 h. More interestingly, before complete amorphization, a sequential disordering of first Ni and then Nb crystalline lattices was observed for the first time, and it was essentially the physical origin of an asymmetric growth of the amorphous interlayer during solid-state reaction reported previously in some binary metal systems. In another two multilayered samples with overall compositions of Ni64Nb36 and Ni70Nb30, thermal annealing under similar conditions resulted in the formation of two metastable crystalline phases with face-centered-cubic and hexagonal-close-packed structures, respectively, although an amorphous phase also appeared and coexisted with one of the metastable crystalline phases in the intermediate states. In the ion mixing experiment, such sequential disordering, as well as formation of metastable phases, was also observed in the respective Ni–Nb multilayers upon room-temperature 200-keV xenon ion irradiation. Comparatively, however, ion irradiation eventually induced complete amorphization in all the multilayers at the respective doses, indicating that ion-induced disordering frequently predominated in the competition between amorphization and the growth of a metastable crystalline phase. A Gibbs free energy diagram, including the free energy curves of the newly formed metastable crystalline phases, of the Ni–Nb system was calculated based on Miedema's model. The constructed free energy diagram can give reasonable explanations of the sequential disordering and the thermodynamic possibility of the formation of either an amorphous or a metastable crystalline phase, of which the free energy difference was quite small. It follows naturally that the phase selection, namely, which phase was more favored to be formed eventually than its competitors, was influenced or even determined by the kinetics involved in the respective processes.

Abstract

Dielectric ceramics in the Li2ZnTi3O8 system were synthesized using TiO2 nanoparticle reagent by the reaction-sintering process. The special effects of the TiO2 nanoparticle reagent on the densification, phase distribution, microstructure, and dielectric properties were characterized using powder x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). A single phase of Li2ZnTi3O8 ceramic was confirmed by the XRD pattern at all temperatures except 1075°C. The reaction between the starting materials was accelerated using TiO2 nanoparticles, with pure Li2ZnTi3O8 phase being created even at low sintering temperature of 900°C, along with increasing green specimen density at the compaction stage. The presence of TiO2 phase in the Li2ZnTi3O8 ceramic improved the \(\tau_\text{f}\) value and shifted it to near zero at 1075°C, and the ceramic exhibited excellent microwave dielectric properties of \(\varepsilon_\text{r}\) = 23.5, \(Q \times f\) = 71,000 GHz, and \(\tau_\text{f}\) = −3.5 ppm/°C.