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As highly integrated circuits are demanded for high-performance electric devices, small sizes of barium titanate (BaTiO3) as a dielectric material are desirable for the application of multilayer ceramic capacitors. Since the small sizes of the particles degrade the dielectric property, especially below a certain critical size, understanding the probable cause is significant for the high-performance capacitors. Here, we have demonstrated nanosized BaTiO3 with average size below 30 nm and a uniform size distribution. High-resolution transmission electron microscopy (TEM) shows that the as-synthesized BaTiO3 contains intragranular pores. We have analyzed the correlation between the intragranular pores inside nanoparticles and their phase ratio of cubic and tetragonal. We have found that the presence of the intragranular pores affects low tetragonality of BaTiO3 particles, and the intragranular pores are generated by the accumulation of hydroxyl groups during hydrothermal reaction. Formation and accumulation of intragranular pores have been investigated by ex-situ synchrotron X-ray diffraction and TEM analysis, suggesting the phase evolution model of nanosized BaTiO3. [ABSTRACT FROM AUTHOR]

This study presents an interesting phenomenon of the simultaneous occurrence of adsorption and synthesis of Mg-Al layered double hydroxide (Mg-Al- LDH) by stirring a precursor in an aqueous solution with methyl orange ( MO) as target adsorbate with the precursor prepared by first milling Mg( OH)2 for 1 h followed by another 3 h milling with Al( OH)3.The prepared precursor and LDH samples were characterized by a set of analytical methods including X-ray diffraction ( XRD), thermogravimetry/differential scanning calorimetry ( TG- DSC), and Fourier-transform infrared ( FT- IR). The maximum adsorption capacity ( Qm) of MO by the prepared precursor sample was 1110.2 mg/g, much higher than that from the synthesized LDH sample. Engineering application may be expected from the easy preparation of such precursor as adsorbent to purify the tremendous amounts of dye wastewater. [ABSTRACT FROM AUTHOR]

Aluminum hydrous oxides and their derivatives were prepared by a facile solvothermal process in the presence of formamide, dimethyl formamide, and diethyl formamide as solvents at 150°C/24 h. The as-synthesized products were calcined at 500°C/1 h to obtain γ-Al2O3. The crystallization behavior and microstructure of the pre- and postcalcination products were studied by X-ray diffraction and transmission electron microscopy, respectively. The surface textural properties of the calcined samples were investigated by N2 adsorption-desorption analysis. The formamide and its derivatives played a significant role in tuning textural properties of the calcined products. The diethyl formamide based sample exhibited enhanced Brunauer-Emmett-Teller surface area and pore volume of 517 m² g-1 and 2 cm³ g−1, respectively. Both the as-prepared and calcined samples showed variable morphologies and crystallinity using different solvents. The trend in morphological changes as nanosheet → nanorod → nanowire bundles occurred in the presence of formamide, dimethylformamide, and diethylformamide, respectively. A tentative mechanism has been illustrated for the formation of the products. [ABSTRACT FROM AUTHOR]

This paper reports a new strainless fabrication method for ytterbium-doped CaF2 laser ceramics involving no drying step before green body casting. The nanoparticles were kept in aqueous solution until green body shaping. Centrifugation was used to obtain correct compactness of the green body before sintering. Characterizations were conducted at different steps of the fabrication process. No grain boundaries oxidation was observed in the sintered ceramics although the nanoparticles were permanently maintained in water until they were sintered. Finally, these ceramics are more homogeneous and have less light scattering defects (no porosity), and present improved optical properties when compared to ceramics obtained from dried nanopowders. [ABSTRACT FROM AUTHOR]

We have successfully synthesized Sn1− xNi xO2 (0.05 ≤ x ≤ 0.15) solid solutions in order to study their structural, optical, and magnetic properties at different Ni concentrations. X-ray diffraction showed monophasic and crystalline tetragonal structure. The shifting of peaks toward higher angle is attributed to the incorporation of Ni2+ ions in SnO2 host lattice. Particle growth restrained upon Ni-doping and found to be in the range of 8-12 nm. Ni-doped SnO2 nanoparticles show blue shift in band gap studies, which is found to be in the range of 3.9-4.1 eV. High surface areas have been achieved for these solid solutions, which come out to be 130, 200, 457, 497, and 680 m2/g, respectively. The solid solutions exhibit paramagnetic behavior along with antiferromagnetic exchange coupling. [ABSTRACT FROM AUTHOR]

The stabilities of Al2O3-Fe2O3-mono ( AFm) and -tri ( AFt) phases in the Ca-Al-S-O-H system at 25°C are examined using Gibbs energy minimization as implemented by GEM-Selektor software coupled with the Nagra/ PSI thermodynamic database. Equilibrium phase diagrams are constructed and compared to those reported in previous studies. The sensitivity of the calculations to the assumed solid solubility products, highlighted by the example of hydrogarnet, is likely the reason that some studies, including this one, predict a stable SO4-rich AFm phase while others do not. The majority of the effort is given for calculating the influences on AFm and AFt stability of alkali and carbonate components, both of which are typically present in cementitious binders. Higher alkali content shifts the equilibria of both AFt and AFm to lower Ca but higher Al and S concentrations in solution. More importantly, higher alkali content significantly expands the range of solution compositions in equilibrium with AFm. The introduction of carbonates alters not only the stable AFm solid solution compositions, as expected, but also influences the range of solution pH over which SO4-rich and OH-rich AFm phases are dominant. Some experimental tests are suggested that could provide validation of these calculations, which are all the more important because of the implications for resistance of portland cement binders to external sulfate attack. [ABSTRACT FROM AUTHOR]

Highly crystallized fine powder of strontium titanate (SrTiO3) was obtained at room temperature simply by leaving a vial containing the powder mixture of Sr( OH)2·8H2O and hydrous titania gel (TiO2· nH2O) for 10 d. Solvent and additive(s) used in the conventional low-temperature process were not used. The crystallinity judged from the FWHM of X-ray diffraction peak was comparable to that obtained by a solid-state reaction. To cause the reaction at room temperature, the titania gel had to contain a considerable amount of H2O ( n > 0.97). The reaction is considered to be neutralization of titanic acid [H4TiO4 or Ti( OH)4] and strontium hydroxide (base). Using similar process, highly crystallized BaTiO3 powder was also obtained at 60°C. In comparison with the formation temperature of BaTiO3, tolerance factor in the perovskite structure was important for the room-temperature synthesis of SrTiO3. SrTiO3 was hardly obtained at room temperature by the addition of saturated strontium hydroxide solution to the hydrous TiO2 gel ( n = 1.29). Therefore, the reaction seems to proceed in the hydrous titania gel. This process is characterized by three important points; 'no solvent', 'no additional reagents', and above all, 'no heating'. [ABSTRACT FROM AUTHOR]

This study has presented synthesis, characterization, and formation mechanism of a kind of novel porous zircon with desert rose-shaped morphology, which was hydrothermally fabricated by a two-step quasi- in situ reaction in a system of silica hydrogel and well-dispersed ZrO2 precursor microspheres. The micro-mesoporous zircon product possesses a sole crystalline phase of hydroxyl-fluorinated ZrSiO4 without unreacted ZrO2 or SiO2 in the final resultant. It has a specific surface area exceeding 120 m2/g and can maintain more than 50% micro-mesoporic pores after calcination at 800°C due to its magnificent thermal stability. A four-stage formation mechanism has been proposed to elucidate the process of quasi- in situ crystallization and growth for the rose-shaped zircon. [ABSTRACT FROM AUTHOR]

Here, we examine the structural, vibrational, optical, and morphological properties of ZnO particles synthesized by the hydrothermal method, incorporating cadmium at different concentrations through the molar ratio Rm = Cd+2/Zn+2 and a thermal treatment at 500°C. The X-ray diffraction results demonstrated the high crystallinity of the ZnO compound with a wurtzite-type hexagonal structure. The Raman scattering spectra demonstrated that the ZnO vibrational modes occur in the region between 200 and 1300 cm−1, which is associated with different vibrational configurations characteristic of the ZnO molecule: E2(Low), E2(M), A1( TO) E1( TO), 2B1(High), E2(High), and TA + LO. The modes that were most affected by the incorporation of Cd2+ were those assigned to 2E2(Low), E2(M), and 2B1(High), and this effect was associated with a greater displacement of Zn2+ ions. The optical study showed a reduction in the band gap and a decrease in the crystalline quality due to the substitution of Cd2+ in the ZnO lattice. Cadmium incorporation affected the morphology of the ZnO:Cd particles, changing the lengths and diameters of the ZnO rods; when the Cd concentration was increased, the ZnO rods shortened, forming coin-type hexagonal structures. [ABSTRACT FROM AUTHOR]

Sodium niobate NaNbO3 hydrate ( NN-hydrate) particles with a plate-like morphology were prepared at 140°C for 2 h in 12 mol/L of NaOH by the hydrothermal method. Bar-like Na8Nb6O19·13H2O particles were synthesized at as low as 100°C for 2 h. This work demonstrates that by carefully optimizing the reaction condition, we can selectively fabricate niobate structures, including the bar-like, plate-like, fibers and cube particles through a direct reaction between NaOH solution and Nb2 O5. It was found that Nb6 O198− formed was an important premise for formation of the NN-hydrate, and lower [ OH-] was not favorable in preparing the NN-hydrate as there was an optimum [ OH−]. Through researching effects of the reaction temperature, time, concentration of NaOH, and content of Nb2 O5 on the NN-hydrate structure and evolution, the formation mechanism from solid reactants to the intermediate were investigated. After calcining at 800°C, the synthesized NN-hydrate particles made a phase almost transform to the perovskite NaNbO3, and the morphology of these calcined particles was still plate-like. [ABSTRACT FROM AUTHOR]

The ability to control the morphology of fluorite-structured cerium oxide nanomaterials is an important step in the design of cerium oxide-based catalysts. Herein, we report an additive-free synthesis of cerium oxide nanorods with highly tunable aspect ratios from ~6:1 to 40:1. The use of a microwave hydrothermal method allows for both rapid synthesis and temperature control. The ability to control the length of the nanorods from <51 nm to >1.7 μm by varying only the reaction temperature was demonstrated over a temperature range of 80°C to 200°C. The formation of the resulting nanorods was investigated using selected-area electron-diffraction and high-resolution transmission electron microscopy. The surface area of nanorod products was found to decrease from 117 to 22 m2/g as the reaction temperature increased from 80°C to 200°C, complementing the general trend of the increasing aspect ratios of these products. [ABSTRACT FROM AUTHOR]

Perovskite ZnZrO3 nanoparticles were synthesized by hydrothermal method, and their microstructures and optical properties were characterized. The crystallinity, phase formation, morphology and composition of the as-synthesized nanoparticles were characterized by X-ray diffraction ( XRD), selected area electron diffraction ( SAED), high-resolutiontransmission electron microscopy ( HRTEM), and energy-dispersive X-ray ( EDX) spectroscopy analysis, respectively. TEM images demonstrated that the average particle size of the ZnZrO3 powders was increased with increasing the Zn/ Zr molar ratios in the precursors, and more large ZnZrO3 particles with cubic morphology were observed at high Zn/ Zr molar ratios. In addition, the phase structures of the ZnZrO3 particles were also evolved from a cubic to tetragonal perovskite phase, as revealed by XRD and SAED patterns. HRTEM images demonstrate that surface structures of the ZnZrO3 powders synthesized at high Zn/ Zr molar ratios, are composed of corners bound by the {100} mini-facets, and the surface steps lying on the {100} planes are frequently observed, whereas the (101) facet isoccasionally observed. The formation of such a rough surface structure is understood from the periodic bond chain theory. Quantitative EDX analyses demonstrated that the atomic concentrations (at.%) of Zn: Zr: O in the particles were 20.70:21.07:58.23, as close to the composition of ZnZrO3. In the optical spectra, a significant red shift of the absorption edges (for the ZnZrO3 nanopowders) from UV to visible region (from 394 to 417 nm) was observed as increasing the Zn/ Zr molar ratios in the precursors, which corresponds to that the band gap energies of the ZnZrO3 nanopowders can be continuously tuned from 3.15 to 2.97 eV. This opens an easy way to tune the band gap energies of the ZnZrO3 nanopowders. [ABSTRACT FROM AUTHOR]

ZnO nanorods have been studied extensively due to facile synthesis and useful optoelectronic properties for applications in nanoscale devices. In a common two-step procedure, an ethanolic Zn2+ precursor solution is used to deposit ZnO seed crystals on a substrate, which is then immersed in an aqueous Zn2+ precursor solution to grow the nanorods. Here, a forced hydrolysis technique was employed based on additions of water and heat to the seed precursor solution before depositing the seeds on commercial fluorine-doped tin oxide (FTO)/glass substrates. ZnO nanorods were then grown from these seeds by chemical bath deposition. Analyses showed that the forced hydrolysis resulted in an increase in seed crystallite size and a decrease in the number of seeds deposited. With increasing seed size, the number density of nanorods decreased, while the length and diameter of each rod increased. These findings offer a simple method for exerting control over the number density of ZnO nanorods that is compatible with the rough FTO surface, unlike other methods that require smoother substrates. [ABSTRACT FROM AUTHOR]

Single- BiFeO3 perovskite films onto Pt-coated silicon substrates have been fabricated by chemical solution deposition using a synthesis strategy based on the use of nonhazardous reagents. Different routes were tested to obtain precursors for the deposition of the films, inferring that bismuth ( III) nitrate and iron ( III) 2,4-pentanedionate dissolved in acetic acid and 1,3-propendiol led to the best solution. Ferroelectric, magnetic, and optical functionalities were demonstrated in these films, obtaining a high ferroelectric polarization at room temperature, ~67 μC × cm−2, a dependence of the magnetization with the film thickness, 0.60 and 2.50 emu × g−1 for the ~215 and ~42-nm-thick films, and a direct band gap in the visible range, Eg ~2.82 eV. These results support the interest of solution methods for the fabrication of BiFeO3 thin films onto the silicon substrates required in microelectronic devices. [ABSTRACT FROM AUTHOR]

Benzyl alcohol route, starting form Fe( III) acetylacetonate, was applied to obtain crystalline magnetite nanoparticles. In particular, the effect of synthesis parameters (time and temperature) and use of SOCl2 on the physical and magnetic properties of the so-obtained powders were evaluated. By means of this approach, monocrystalline magnetite particles with size ranging from 5 to 15 nm were obtained. [ABSTRACT FROM AUTHOR]

Different types of tetragonal BaTiO3 particles were synthesized in a wet chemical process including an autoclave treatment. The synthesis and autoclaving medium was varied from isopropyl alcohol to water in different ratios, leading to a size variation of the particles from 38 to 145 nm. By applying combustion analysis of carbon and hydrogen (C/H analysis) released from the samples, it can be demonstrated that the amount of hydroxyl impurities incorporated into the crystal lattices of the particles increases with the water content of the synthesis medium. C/H analysis is a suitable tool for this characterization task as it allows discriminating different sources of these elements, i.e., different impurities. By comparing the self-synthesized particles with commercial ones, it can be concluded that the particle size has the dominant influence on the tetragonality, if the amount of internal hydroxyl groups is relatively low. In contrast, if the amount of water originating from the internal OH groups is elevated (greater than ~0.4 wt%) an impairment of the tetragonality is caused. [ABSTRACT FROM AUTHOR]

Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H2PO4)3]. Two different amounts of Al(H2PO4)3 were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG-DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low-viscosity and high-concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride ( BN) powder bed followed by ultrasonic washing of the AlN granulates/ BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs. [ABSTRACT FROM AUTHOR]

Nanocrystalline TiO2 and Ti1− x V x O2 ( x = 0.01) powders have been prepared by thermal decomposition, in air, of amorphous precursors resulting from the freeze-drying of appropriate solutions. In addition, TiO2− x N y (anatase and rutile) and Ti O x N y (rock-salt) have been prepared by thermal treatment in ammonia of a crystalline precursor ( TiO2 obtained at 673 K). TEM and SEM images, as well as the analysis of the X-ray diffraction ( XRD) patterns, show the nanoparticulated character of those solids obtained at low temperatures, with typical particle sizes in the 10-20 nm range when prepared at 673 K. The UV-Vis results indicate both the insertion of V in the anatase lattice and the feasibility of nitridation at low temperatures. The photocatalytic properties of these materials (as prepared and after their incorporation to mortar samples) in the degradation of nitrogen oxides have been preliminary evaluated. Although N-doping enhances the photocatalytic activity of the TiO2 matrix, V-doping worsens it. [ABSTRACT FROM AUTHOR]

Uniform alumina microfibers precursor (ammonium aluminum carbonate hydroxide, AACH) were successfully synthesized using the microwave hydrothermal method, with average length of 5-10 μm and the diameter around 300-500 nm. FT- IR spectra indicated AACH was composed of NH4[ Al( OOH) HCO3]· H2 O. The thermal behaviors of the as-prepared AACH were investigated using differential scanning calorimeter and thermogravimetric analysis ( DSC- TG), XRD, and SEM. The results showed that the thermal decomposition of the AACH microfibers occurred via three steps, which were respectively divided into adsorption of physical water, dehydration of crystalline water, and decomposition of AACH. The activation energies for the above three steps were calculated using Coats-Redfern method. The phase transformation sequence was found to be AACH→ amorphous Al2 O3→ γ- and θ- Al2 O3→ α- Al2 O3. It was also observed that the thermal treatment had little influence on fiber morphology of the products. The fibers morphology with high thermal stability will endow to prepare alumina microfibers with novel application potentials. [ABSTRACT FROM AUTHOR]

This study intends to clarify the discrepancies on the effect of precursor size, chemical composition, and thermal behavior of Na-titanate obtained through a conventional hydrothermal reaction of anatase in a highly concentrated aqueous NaOH solution. According to experimental results, as well as that presented in related literatures, ultrafine anatase precursor favors nanofiber formation, whereas larger-particle anatase precursor forms nanotubes. The formation mechanism, in correlation with the precursor size and the resulting morphology of the obtained titanate product, is described in detail. According to X-ray Diffraction and Raman analyses, the as-formed Na-titanate is considered a quasi-disordered structure that allows the occupation of a wide range of Na into the titanate structure. An increased Na/ Ti ratio is observed with increased temperature, which simultaneously results in a distortion of the titanate structure. Moreover, the as-synthesized Na-titanate is thermally unstable and tends to degrade into amorphous clusters after heat treatment at 300°C. Rod-like Na2 Ti6 O13 is recrystallized from the amorphous cluster at 700°C-800°C and becomes plate-like after annealing at 900°C via a parallel assembly of Na2 Ti6 O13 rods. An additional Na2 Ti3 O7 phase appears at high temperatures, exhibiting a relatively higher Na/ Ti ratio. [ABSTRACT FROM AUTHOR]

Rutile powder was synthesized via sol-gel processing of Tyzor TE precursor in an aqueous solution at 40°C-50°C. A suite of characterization techniques, including FTIR, Raman, X-ray, and electron diffraction, were employed to investigate the microstructural evolution. The synthesized powder was phase-pure rutile possessing high surface area (144.7 m2/g), an average pore size of 24.9 nm, and pore volume of 0.66 cm3/g. A reaction mechanism is proposed for the preferential evolution of rutile over other titania polymorphs (i.e. amorphous or anatase). [ABSTRACT FROM AUTHOR]

Single-phase lead lanthanum zirconate titanate (PLZT) solid solution powder was synthesized from the constituent oxides at ambient temperature through a mechanical alloying (MA) process and was then densified to fine-grained ceramics by sintering and hot-pressing. The anomalous photovoltaic effect (APV) and photoinduced strain of the resultant PLZT ceramics were investigated and analyzed in association with the influence of grain size. It was found that a photoinduced voltage up to 6000 V·cm-1 can be obtained as the grain size is reduced to 0.42 μm. This is extremely high and about three times that achievable in normal micrometer-grained PLZT ceramics. The maximum photoinduced strain of the PLZT ceramics with an average grain diameter of 0.54 μm reached 0.01%, which is equivalent to electric-field-induced strain of common piezoelectric materials. [ABSTRACT FROM AUTHOR]

The sintering behavior and piezoelectric properties of the lead zirconate titanate (Pb(Zr,Ti)O3, PZT)—lead zinc niobate (Pb(Zn⅓Nb2/3;)O3, PZN) system were investigated. The sintering temperature required for full densification of the PZT-PZN system was significantly lowered when the proportion of PZN was increased. The density of the specimen composed of 60% PZT and 40% PZN (0.6PZT-0.4PZN, Pb((Zr0.47Ti0.53)0.6-(Zn⅓Nb2/3).04)O3) sintered at 880°C for 4 h was 8.15 g/cm³, which was >97% of the theoretical value. This improved densification behavior was attributed to the combined effects of the high sinterability of PZN and the stability of the PZT perovskite structure. The piezoelectric and dielectric properties of the 0.6PZT-0.4PZN specimen sintered at 880°C were comparable with those of a specimen with the same composition sintered at 1200°C for 2 h. The piezoelectric coefficient (d33) and the electromechanical coupling factor (kp) of the 0.6PZT-0.4PZN specimen sintered at 880°C were 460 pC/N and 0.6, respectively. [ABSTRACT FROM AUTHOR]