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λ-Ti3O5 is a promising phase-transition metal oxide for the application in rewritable data storage, heat storage and smart optoelectronic devices due to its bistable metal-semiconductor transition (MST) characteristics between λ and β phase. However, λ-Ti3O5 is a room-temperature metastable phase and it's synthesis has been a great challenge. This paper presented a magnesium (Mg)-doping strategy for phase control of Ti3O5 to obtain the λ-Ti3O5 via carbothermal reduction method. The results revealed that Mg-doping induced a crystal-structure modification in Ti3O5 by tuning the Mg-doping content. Particularly, it suggested that the phase-transition temperature (Tc) of β–λ was reduced efficiently by increasing the Mg additive amount, and the λ phase was stabilized at room temperature eventually. Electrical resistivity measurement demonstrated a remarkable decrease in resistivity of Ti3O5, indicating a β–λ–α phase evolution induced by Mg-doping. In-situ temperature-dependent XRD was also employed to confirm the phase evolution and phase-transition characteristic of Ti3O5. This work offered considerable insights into a controllable crystal-structure modification for Ti3O5 by a doping strategy and the mechanism to the stabilization of metastable λ-Ti3O5.

Vanadium dioxide (VO2) with reversible metal-semiconductor transition is one of the most researched smart materials due to its near room-temperature transition at around 68 °C. Coating VO2 (M) nanoparticles onto substrate is superior to fabrication of VO2 (M) thin films owing to its advantages on large-scale preparation and flexible shaping. In this study, freeze-drying has been applied in a convenient precipitating and following annealing process of fabricating VO2 (M) nanoparticles. More importantly, effects of freeze-drying and pre-freezing temperature on phase composition, size distribution and phase-transition temperature of synthesized particles have been systematically researched by varying the pretreatment conditions. It is observed that the application of freeze-drying is crucial to the formation of pure VO2 (M), meanwhile, phase-transition temperature and size distribution of VO2 (M) nanoparticles can be effectively reduced with lowered pre-freezing temperatures. Besides, the influence of different annealing temperatures on nanocrystallite size has been investigated, and it has been found that both the crystallinity and particle size increased as the annealing temperature was increased. Finally, the as-fabricated VO2 (M) particles were coated onto microscopic glass substrate to characterize mid-infrared modulation performance. The coated film (made from sample pre-frozen at −50 °C) exhibits an excellent mid-infrared transmittance change of 23.3% at a fixed wavelength of 4 μm. This work demonstrates the effect of freeze-drying on the fabrication of VO2 (M) nanoparticles and provides a facile method for large-scale preparation of VO2 (M) nanoparticles.

λ-Ti3O5 with unique phase transition properties is prosperous functional materials for application in data storage, thermal storage and optoelectronic devices. However, the synthesis of λ-Ti3O5 nanocrystal has long been a great challenge. In this work, the λ-Ti3O5 nanocrystals were obtained by a PEG assisted sol-gel method, in which Polyethylene glycol 600 (PEG-600) was used as a reducing agent. Subsequently, the as-prepared λ-Ti3O5 nanocrystals were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectrum. We also investigated the thermal-induced phase transition characteristics of λ-Ti3O5 by in-situ temperature-dependent XRD. This work provides a facile method to fabricate λ-Ti3O5 and would be significant for the further investigation and application of λ-Ti3O5.

Vanadium dioxide (VO2) is considered to be one of the most competitive thermochromic materials, due to its semiconductor-metal phase transition characteristics. And the doping of tungsten (W) into the lattice of VO2 can significantly reduce the phase transition temperature to near room temperature. However, the reduction efficiency dependent on doping amount is quite different in previous reports. In this work, we proposed an in-situ stirring assisted hydrothermal to synthesize W-doped VO2 nanorods with improved doping efficiency. The effects of in-situ stirring during the hydrothermal synthesis on phase composition, sample morphology, and phase-transition temperature of VO2 with different W doping amounts were studied systematically. The phase transition temperature reduction efficiency of W-doped VO2 prepared by hydrothermal synthesis without in-situ stirring was at % W. By contrast, the phase transition temperature of W-doped VO2 prepared by in-situ stirring hydrothermal synthesis was depressed as much as 24.55 °C/at % W when W/V ranged in 0.75–2.0 at %. Further research found that the phase transition temperature of W-doped VO2 (M) could be simply tuned by changing the in-situ stirring time. Then, the 1 at% W-doped VO2 (M) (with phase transition temperature of around 41.5 °C) nanorods and acrylic resin were mixed to prepare VO2 composite film. It exhibited suitable infrared transmission (>60%) and excellent mid-infrared transmission switching performance (23.77%). This work proposed an in-situ stirring hydrothermal method for high efficiency synthesis of W-doped VO2 (M) and provided significant insights for its application in thermochromic windows.

λ-Ti3O5 powders were prepared by carbothermal reduction of nano-TiO2 (coated by inorganic) in argon atmosphere. The compound formation mechanism was described as well in this rote. The products synthesized under different heating temperatures, nano-carbon black contents and argon flow rate were investigated by X-ray diffraction (XRD). It indicated that high purity λ-Ti3O5 powders have been obtained by carbon black content of 4.5 wt% at 1050 °C for 3 h in argon flow rate 0.5 L min−1. The morphology of λ-Ti3O5 powders was characterized by scanning electron microscope (SEM). Meanwhile, the optical property of obtained λ-Ti3O5 powders was analyzed by ultraviolet–visible (UV–Vis). The results showed that the average size was about 3.0 ± 1.0 μm and the specific surface area (BET) was 12.82 m2 g−1. λ-Ti3O5 powders exhibited high absorption in the optical absorption bands ranging from 200 to 1400 nm. The isolation of λ-Ti3O5 can be obtained from as-prepared samples by NaOH etching, as demonstrated by Raman spectra. The conductivity of samples was 0.68 Ω cm−1 while it was 3.14 × 10−2 Ω cm−1 after etching.

Synchrotron X-ray radiography was used to in situ study the interface diffusion behavior and microstructural evolution during the melting and solidification of Al/Cu bimetal. During the solidification, the dendritic growth around the interface is mainly dominated by the variation of Cu concentration and thermal field. Four transition zones of solute profile around the interface were identified to be I (alpha-Al), II (Al + Al2Cu), III (Al2Cu) and IV (AlCu, Al3Cu4 and Al2Cu3), respectively. During the melting, the concentration variations of Al and Cu around the interface were quantitatively analyzed through the extraction of gray level from sequenced X-ray images. The diffusion coefficients of Cu in liquid Al were calculated from the known concentration variations by an inverse method based on Fick's second law. The diffusion coefficients of Cu in Al were found to follow linear Arrhenius equation dependencies with the pre-exponential factor of 2.83 x 10(-5) m(2) s(-1) and the activation energy of 96.0 kJ mol(-1) in a temperature range of 893-970 K. (C) 2014 Elsevier B.V. All rights reserved.