In this review, research on the preparation and characterization of TiO2-containing nanocomposites is considered. The preparations of nanocomposites by sol–gel and anodization methods are mainly explored. Nanocomposites are highly desired for some applications, and the means of controlling their functions to optimize performance is reviewed. The typical applications of TiO2-containing nanocomposites in photocatalysis and micropatterning are discussed.
Growth of amorphous ZnO by B doping and their opto-electrical properties are reported. The B-doped ZnO (ZnO:B) films were grown by pulsed laser deposition using polycrystalline ZnO:B ceramic targets. Although the solubility limit of B in bulk ZnO polycrystal was ~4%, 18%-doped ZnO:B showed the shrinkage in the c-axis length. Preferentially (002)-oriented polycrystalline ZnO:B films were grown for the B concentration [B] ≤ 18%; while, amorphous ZnO:B films were obtained for [B] ~26%. It was found that the density of the amorphous ZnO:B film was smaller by 9% than that of crystalline ZnO (5.61 g·cm−3), which is explained mainly by the incorporation of the light B atoms. The optical bandgap of the ZnO:B films increased with [B] and that of the amorphous ZnO:B film was ~3.38 eV. The amorphous ZnO:B films have low free electron density of ~1015 cm−3, suggesting the existence of electron traps. Hall mobility of the amorphous ZnO:B [~1 cm2(V·s)−1] was smaller than those of the polycrystalline ZnO:B films.
The present work aims at exploitation of CKD in presence of quartz sand by its conversion into eco-friendly wollastonite ceramics. Different batch compositions of cement kiln dust (CKD) with 30 to 55 wt % quartz with an increment of 5 wt % were designed to prepare wollastonite and its composites. The batches were designated as B30, B35, B40, B45, B50, B55 where the number indicates the weight percent of quartz in the batch composition and the rest is cement kiln dust. These batches were wet mixed, dried at 100°C for 24 h, grounded, sieved, uniaxially pressed and fired at different temperatures. Phase composition, microstructure, densification parameters, and mechanical properties of the obtained fired specimens were investigated. The results showed that α- & β-wollastonite polymorphs and their composites were synthesized successfully at lower temperatures (1150–1250°C) without addition of any mineralizers. The output of this work might be considered as a real solution for the environmental problem relevant to cement industry.
Amorphous InGaZnO4-xSx thin films were fabricated using a polycrystalline InGaZnO4 target by pulsed laser deposition in an H2S gas flow. The optical band gap first decreased from 3.05 to 1.65 eV as x increased from 0 to 1.5, and then increased to 2.6 eV at larger x, showing a bandgap bowing behavior. All the sulfur-containing films have high resistance beyond our measurement limit. Film density of the a-InGaZnS4 film was decreased by ~40% from that of a-InGaZnO4. Density functional theory calculations were performed to explain these results.
β-Sialon based composites were produced using a vertical reactor by carbothermal reduction reaction under nitrogen using fly ash and lignite chars to examine the effects of mixing, carbon content, reaction temperature and sintering time. The influences of chars as a reductant were further investigated in comparison with graphite. The evolution of phase and morphology in samples were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Mechanical stirring was favored to mix fly ash and chars, while ball-milling shove the chars with porous structure due to collisions of agate balls, preventing N2 penetration to the inner parts of reactants. When excess carbon was increased to 100%, a higher combustion reactivity of low-temperature chars resulted in the production of SiC phase. The evolution of β-Sialon with increasing reaction temperature showed the samples mixed with chars were more sensitive to reaction temperature than that with graphite. β-Sialon phase increased gradually with increasing sintering time to 6 h and decreased thereafter due to the decomposition or conversion of β-Sialon. These changes were more significantly for samples adding lignite chars. The optimal operation has been determined and rod-like β-Sialon whiskers with high aspect ratio appeared after performing the operation. In the growth process of whiskers, bead-shape whiskers were observed, suggesting that the growth mechanism was different from the conventional vapor–liquid–solid (VLS) mechanism.
Al2O3 nanoparticle doped SiO2-PVA nanocomposites were prepared using fumed silica, fumed alumina, and poly(vinyl alcohol) (PVA). Nanocomposites containing from 0 to 6 mol % Al2O3 were heat-treated in air at 1100 to 1300°C to obtain monolithic, transparent silica glass. The 0.6 mol % Al2O3 doped nanocomposite was sintered at 1200°C, a higher temperature than was required for the non-doped nanocomposite. The obtained Al2O3 doped silica glass exhibited characteristic blue photoluminescence (PL) on UV excitation. The effects of the Al2O3 nanoparticles on the sintering temperature and the PL characteristics of the sintered silica glass are discussed in terms of the morphology and structure of the sintered glass.
This article reports a novel method of sintering zirconium oxalate (ZrOC2O4) sol to prepare dense yttria stabilized zirconia (YSZ) ceramic at a low sintering temperature below 1300°C. A YSZ ceramic as control group was also prepared by sintering its nano-powder. The thermal decomposition process and sinter programme of the YSZ green bodies were investigated by thermogravimetry and differential thermal analysis. The sintered ceramics showed a crystallization structure in cubic phase and the crystallite size increased with the increasing sintering temperature in the range of 550 to 1200°C. For preparing dense YSZ ceramic, a zirconium oxalate sol was prepared by sol–gel method and then sintered with a temperature of 1000, 1100, 1200 and 1300°C. Compared with the ceramic obtained from YSZ ceramic nano-powder, the ceramic prepared by zirconium oxalate sol exhibited an enhancement of densification with higher relative density of 98.5% and higher electrical conductivity at all test temperatures.
The microstructure of Li0.06Na0.52K0.42NbO3 piezoceramics was designed and controlled by the use of additives such as Li2CO3, SiO2, MnCO3, and SrZrO3. The electric and piezoelectric properties, microstructures, and compositional distribution of the additive elements are investigated in this paper. The average grain diameters decreased from 5.8 to 3.0 µm when the following additives were incorporated: 0.65 mol % Li2CO3, 1.3 mol % SiO2, 0.2 mol % MnCO3, and 0.5 mol % SrZrO3. In addition, the maximum grain diameters decreased from 15 to 7.7 µm. The compositional distributions were analyzed by energy dispersive X-ray spectrometry using a transmission electron microscope. Grains of SiO2 glass and the MnO compound were evaluated as diverse grains on the ceramic matrix. Because of the homogenization of the microstructure and the increased relative density, the resistivities were increased over the whole measuring temperature range. For example, the resistivities increased from 5.2 × 109 to 2.7 × 1010 Ω·cm at 160°C. The piezoelectric properties remained about the same: εT33/ε0 = 880, tan δ = 1.9%, kr = 41.8%, d31 = −74 pC/N, and Tc = 470°C. These results indicate an improvement in the reliability of structural refinement techniques for ceramics.
(1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT) (x = 0–1) epitaxial thin films with high crystallinity have been prepared by using metallo-organic decomposition (MOD) processes at a temperature half of the crystallization temperature of the corresponding bulk crystals. X-ray diffraction patterns show that Ti-poor and Ti-rich PMN–PT thin films have perovskite-type structure with a single phase of pseudocubic and/or tetragonal phase, respectively. The morphotropic phase boundary (MPB) is located around x = 0.6. Chemically-ordered regions (CORs), where Mg and Nb ions at B-sites show 1:1 ordered structure in the 〈111〉 directions, are clearly detected by using aberration-corrected high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images taken along the 〈110〉 directions, while it is difficult to analyze the detailed structure of the CORs by the electron or X-ray diffraction methods owing to the small volume. It showed that the density of COR rapidly decreases with increasing the Ti concentration, keeping the size of each COR, which infers that the COR may vanish at the Ti composition less than MPB. STEM analysis around the film/substrate interface shows the elastic interaction between CORs and local strain fields would be weak.
In this study, in order to improve interfacial strength between CNFs and SiC matrix and to disperse CNFs uniformly in the SiC matrix, using the SiC-coated CNFs which were prepared using SiO2 powder at 1400–1800°C in argon atmosphere, CNFs/SiC composites were fabricated in argon atmosphere under pressureless condition. The non-coated CNFs/SiC and SiC-coated CNFs/SiC composites reached near the full density at 2150°C. The SiC grains and the carbon agglomerates in the composites tended to be finer with an increase in amount of SiC coating on CNFs. The SiC-coated CNFs/SiC composites showed almost the same fracture toughness (4.5–5.0 MPa·m0.5) with the non-coated CNFs/SiC composite. On the other hand, the SiC-coated CNFs/SiC composites showed higher bending strength than the non-coated CNFs/SiC composite, and the bending strength became higher with an increase in amount of SiC coating on CNFs. The maximum bending strength was 551 MPa, which represent a 32% increase compared with that of the non-coated CNFs/SiC composite.
We study atomic and electronic structures of hexagonal boron nitride (h-BN) bilayers on the basis of the first-principles density-functional calculations. The interlayer distances between two atomic layers in h-BN bilayer and the band gaps are calculated under biaxial tensile strains. It is found that the interlayer distances are changed when the tensile strains are applied. It is also found that the band gap decreases as the tensile strain increases. The band gaps of h-BN bilayer are tunable by biaxial elongations.
Single-crystalline BaTiO3 nanocubes were synthesized by hydrothermal method using water-soluble titanium complex and surfactants. The highly-ordered assemblies of BaTiO3 nanocubes were directly fabricated on the substrates with micro-patterns by the dip coating method with a low upstroke operation rate. The micro-patterns which had micro-trenches parallel to the upstroke operating direction affected the formation of nanocube assemblies and enabled to fabricate assemblies with average size of about 40 µm in length and width of 2 µm. The micro-patterned polyimide substrate affected the capillary force and enhanced the ordering degree and density of the nanocube packing. This method has an advantage to suppress generation of micro-cracks and to form micro-patterning the BaTiO3 nanocube assemblies.
The electrical characteristics and interfacial trap levels at grain boundaries of SrCoO3 (SCO, 0.25–3.0 mol %)-added ZnO varistors were investigated. A marked nonlinearity was observed in the V–J characteristics. The resistance to electrical degradation correlated with the orientation of the (100) plane of ZnO grains: the resistance was large when the (100) plane was parallel to the electrode. Isothermal capacitance transient spectroscopy revealed two kinds of interfacial trap levels. The deeper level was observed in all samples. The shallower level was observed only in samples with 2.5 mol % or more added SCO. Each trap level had a concentration that increased in proportion to the temperature. At room temperature, the concentrations of all trap levels in samples with 2.0 mol % or less SCO were much lower. As a result, no transient capacitance was observed under an applied bias voltage. This suggests that the main cause of the nonlinearity observed in V–J characteristics of samples with 2.0 mol % or less SCO was not the presence of interfacial trap levels, but rather the Co and/or ZnSrO2 in the ZnO grains.
The structural variation of Li2MnO3 during charge–discharge cycling as a lithium-battery cathode was investigated. The Rietveld refinement of neutron diffraction data revealed that the Li2MnO3 synthesized at 900°C was assigned to the monoclinic symmetry corresponding to the C2/m space group (z = 4). The transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements were carried out using the samples after cycling in the potential ranges of 2.0–4.6, 2.0–4.8, and 2.0–5.0 V. As a result, it was observed that structures based on the cubic (Fd3m) and rhombohedral (R3m) symmetries, having the compositions of LiMn2O4 and LiMnO2, respectively, are locally generated on the surface of the particles, depending on the upper voltage for the charge process. It was also found that the voltage at which the R3m rhombohedral structure is generated tended to be higher than the voltage at which the Fd3m cubic structure is formed. Such a structural variation of Li2MnO3 is anticipated to be related to the extraction of oxygen molecules which is induced during the charge processes. Furthermore, the generation of the R3m LiMnO2 could be understood by the introduction of oxygen vacancies into the material.
Hercynite as a kind of chrome-free and environmental friendly material is widely investigated. In this work, hercynite with high purity was synthesized using Fe2O3 and Al2O3 as raw material with SiO2 addition under controlled temperature and atmosphere system. The phase and microstructure of the obtained product were investigated using XRD, SEM and TEM techniques. The effect of SiO2 on the synthesis of hercynite with high purity was discussed from both theoretical and experimental aspects. The results show that SiO2 addition lowers the formation temperature of the liquid phase, which promotes Al2O3 to melt into the liquid phase and makes the formation of hercynite possible during the heating stage. During the process of crystallization, SiO2 further facilitates the formation of hercynite by the peritectic reaction. During the fast cooling stage, SiO2 in the form of amorphous silicate exists between hercynite crystals. Therefore hercynite with high purity and dense structure is successfully synthesized. It also shows that 1 mass % SiO2 addition can effectively promote the crystal growth of hercynite and thus lead to dense structure.
Kinetic study was done for the decomposition process of lysozyme (LSZ) on the surface of Ti(IV)-doped calcium hydroxyapatite (TiHap) particles. The decomposition of LSZ was examined by changing the weight of TiHap particles dispersed and reaction temperature. The decomposition of LSZ was analyzed by using the first order reaction. The obtained data fairly fit to the first order reaction equation, and the rate constant (k) was obtained. Since a good linear relationship was obtained between k values and particle weigh of TiHap, it was concluded that the decomposition of LSZ molecules occurs on the surface of TiHap. The activation energy of the reaction of LSZ decomposition on the surface of TiHap particles was determined as 30.2 kJ/mol by varying the decomposition temperature from 5 to 45°C. The comparison experiments between 0 h UV and 24 h UV methods revealed that the decomposition of LSZ needs appropriate rates of adsorption and decomposition at the TiHap particle surface. It was ascertained that the decomposition temperature at 25–45°C is appropriate to proceed continuous decomposition of LSZ for a long time. The LC-MS measurements reveled that LSZ molecules were decomposed to the small molecules with molecular weight of 1/35–1/50 to LSZ one and they converged to the compounds with low molecular weight of 288–316 after a long time UV irradiation.
Ternary composites of ZrC–ZrB2–SiC were successfully synthesized via spark plasma sintering at 1600, 1700 and 1800°C for 5 min under a pressure of 40 MPa with ZrB2, ZrC and SiC powder as the raw materials, respectively. The microstructures, phase composition and mechanical properties were studied by scanning electron microscopy, X-ray diffraction and three-point bending test, respectively. The relative density, apparent porosity and flexural strength of the ZrC–ZrB2–SiC composite were 93.1%, 0.89% and 383.15 ± 13.56 MPa at 1800°C, which showed the preferable mechanical property and denser microstructure than these properties of 88.0%, 1.68%, 369.77 ± 12.73 MPa at 1600°C and 90.1%, 1.20%, 379.71 ± 12.44 MPa at 1700°C. The comparison showed 1800°C was the best sintering temperature that the ternary composites owned the best microstructures, phase composition and mechanical properties in this experiment.
We prepared SnO–ZnO–B2O3 system glasses by means of melt-quenching technique with different melting-process temperatures in range of 1100–1500°C, and examined the impact of the process temperature on photoluminescent (PL) property. The glass obtained at 1100°C showed clear PL band at ∼2.8 eV at room temperature. As elevating the process temperature, a shoulder appeared at lower-energy side of the PL band, and eventually broad band with peak at ∼2.2 eV developed, resulting the clear orange PL. We demonstrated that the PL-color is controllable from blue to orange via white by change in the process temperature.
The diffusion of silver, Ag, as the electrode material in (Bi1/2K1/2)TiO3 (BKT) ceramic were studied by means of a secondary ion mass spectrometry (SIMS). Some analytical methods of SIMS were applied to obtain Ag diffusion coefficient in BKT ceramics. Depth profile of Ag showed a simple concentration gradient from the surface towards the deeper side in BKT ceramics. From these profiles, the diffusion coefficients of Ag were calculated and obtained by the analysis. The temperature dependence of Ag diffusion in BKT ceramics was described by 2.2 × 106 cm2/s of pre-exponential factor and 296 kJ/mol of the activation energy in the temperature range of 700–900°C as diffusion treatments.
A printable semiconductor based on the V2O5–P2O5 system for thermoelectric (TE) applications was fabricated by treatment under reductive conditions. 65V2O5–15P2O5–15CuO–5Fe2O3 (Tg∼305°C) glass films with a thickness of ∼40 µm were prepared on polycrystalline α-Al2O3 substrates via a melt-quenching synthesis, subsequent milling and powder application, and then a viscous flow in air. The glass films heat-treated at 450–650°C in ultra-high vacuum (UHV; ∼1 × 10−6 Pa) and further reductive hydrogen atmosphere indicated advanced crystallization at the higher temperature, and the reduction demonstrated by the increase of V4+/V5+ and Cu1+,0/Cu2+ ratios. The surface morphology of the crystallized films demonstrated significant crystal growth up to ∼5 µm with increased heating temperature in UHV as well as a change in their characteristic shapes. Nano and micropores were homogeneously dispersed throughout the film crystallized at 450°C in UHV, which reduced thermal conductivity. The hydrogen treatment resulted in a volume shrinkage of the precipitated crystals, which is assumed to be due to the reduction and desorption of volatile components. The temperature dependency of the resistivity and the Seebeck coefficient of the crystallized glass-ceramic films were measured. The glass-ceramic films revealed semiconductor behavior in resistivity, and the precipitation in UHV at 650°C decreased the resistivity to 7 × 10−2 Ωcm at 300°C. A lower resistivity of 2 × 10−2 Ωcm was obtained after reduction by hydrogen. The films crystallized in UHV at 550 and 650°C had Seebeck coefficients lower than −120 µV/K and were almost flat in the temperature range 50–300°C. On the other hand, the hydrogen-treated films revealed a Seebeck coefficient of ∼+10 µV/K. It is noteworthy that both n- and p-type TE semiconductors were fabricated from the same starting V2O5–P2O5 glass system.