Search

A novel, facile nonaqueous synthesis route to nanocrystalline lead zirconate titanate (PZT) powders is presented. Simple mixing of lead acetylacetonate with titanium and/or zirconium alkoxides in 2-butanone, followed by a solvothermal treatment at 200 °C, produced amorphous, nanosized precursor powders. According to X-ray diffraction and transmission electron microscopy investigations, calcination at comparably low temperatures yielded highly crystalline, phase-pure powders consisting of monocrystalline particles in the size range of about 10−30 nm. Thermogravimetric and infrared analyses of the as-prepared samples showed a content of organic species of about 10 wt %, which are decomposed between 200 and 330 °C. The lack of further weight loss above 400 °C proves the absence of PbO evaporation, a major drawback of previous PZT preparations. Crack-free thin films were obtained by simply casting a dispersion of precursor powders on a silicon substrate followed by thermal treatment. Scanning electron microscopy shows homogeneous films to some extent populated with regular, micrometer-sized spheres. However, thorough washing removed most of these larger objects to leave a plain film. According to atomic force microscopy measurements, the roughness of this film is in the nanometer-size regime, confirming that this route is a potential way to fabricate thin homogeneous piezoelectric films.

A novel nonaqueous route has been applied for the preparation of nanocrystalline magnetite. In a simple one-pot reaction process, iron(III) acetylacetonate was dissolved in benzyl alcohol and treated in an autoclave between 175 and 200 °C. This approach leads to monocrystalline magnetite particles with sizes ranging from 12 to 25 nm, as evidenced by X-ray analysis, HRTEM, and Raman and Mössbauer spectroscopy. The isolated particles can be redispersed either in polar or nonpolar solvents by coating them just after synthesis with undecanoic acid or dopamine. Simple sedimentation after redispersion in hexane can be used to lower the polydispersity of the sample.

Ce1-xZrxO2 nanoparticle sols (x = 0−1) are synthesized by hydroxide coprecipitation of a mixed precursor solution of cerium ammonium nitrate and zirconyl chloride followed by redispersion in an aqueous medium by sonication using nitric acid as the peptizing agent. The obtained sols are highly concentrated and stable for weeks. Analytical ultracentrifugation measurements show a particularly narrow particle distribution with an average particle size of about 3.5 nm for pure CeO2 and 2.5 nm for pure ZrO2 nanoparticles. Wide-angle X-ray scattering (XRD) as well as high-resolution transmission electron microscopy give evidence that all of the as-synthesized nanoparticle sols with a ceria content larger than 20 mol % are well crystalline. The formation of a solid solution with an increasing amount of Zr was monitored by XRD and Raman spectroscopy.

The reaction between titanium tetrachloride and benzyl alcohol in the presence of enediol ligands such as dopamine and 4-tert-butylcatechol provides a simple nonaqueous route to in situ surface functionalization of titania nanoparticles. The as-prepared precipitates are resoluble either in water or in organic solvents, depending on the ligand used. The surface chemistry of the 4-tert-butylcatechol-functionalized particles dissolved in dimethylformamide was analyzed by ¹H NMR measurements revealing the presence of adsorbed 4-tert-butylcatechol, in addition to benzyl alcohol and water. Although the reaction temperatures of 70 or 80 °C are relatively low, XRD and HRTEM investigations give evidence that the as-synthesized nanoparticles are highly crystalline. Ultracentrifugation analysis of dopamine-functionalized titania nanoparticles dissolved in water shows a particle size distribution of approximately 3.5−8 nm with the peak maximum at 5.5 nm. Furthermore, the UV−vis detector system of the ultracentrifuge allows the measurement of the absorption spectra dependent on the particle size, showing an unusual red shift with decreasing particle size.

The reaction between TiCl4 and benzyl alcohol is a simple and nonaqueous procedure for the synthesis of highly crystalline titania nanoparticles at temperatures as low as 40 °C. XRD measurements prove the exclusive presence of the anatase phase. The particle growth depends strongly on temperature so that with the appropriate thermal conditions the particle size can be selectively adjusted in the range of 4−8 nm. Fine-tuning of the particle size is possible by a proper choice of the relative amounts of benzyl alcohol and titanium tetrachloride. Lowering the titanium tetrachloride concentration leads to a considerable decrease of particle size. BET measurements show particularly high surface areas, up to 345 m²/g for the smallest particles and 115 m²/g for the calcined material. TEM investigations reveal that the nanoparticles are nearly uniform in size and shape. The as-synthesized particles display only minor agglomeration, whereas the calcined material consists of completely nonagglomerated particles, with diameters ranging from 13 to 20 nm. The smallest particles are soluble in a THF/trioctylphosphine mixture that luminesces (425 nm) upon UV irradiation.

A simple procedure that applies a hexanuclear iron−polyolate complex as an iron oxide precursor has been developed for the synthesis of colloidal iron oxide particles. The hydrolysis of this complex and the subsequent hydrothermal treatment of the intermediate product yield monodispersed hematite particles with a disclike shape. The outer diameter is about 1 μm and the thickness about 250 nm. The particles consist of small platelike crystallites that are almost perfectly aligned in the a−b plane. If acetyl acetone is added during the synthesis, similar but smaller disclike hematite particles (diameter ~ 0.25−0.45 μm, thickness ~ 80 nm) have been obtained. On the other hand, hydrazine as an additive leads to single crystals of hematite in the form of hexagonal platelets (diameter ~ 0.6−1 μm, thickness ~ 50 nm).

The synthesis of vanadium oxide nanotubes (VOx-NTs) containing primary monoamines with long alkyl chains has been achieved by two new approaches, using either VOCl3 or V2O5 as vanadium oxide precursor. The hydrolysis of amine complexes of VOCl3 involves a ligand-assisted templating mechanism as well as the intercalation of amines in layered V2O5. Both procedures followed by a hydrothermal treatment lead to VOx-NTs as the main product. The structure and morphology of the tubes obtained have been investigated and are discussed in terms of comparison with those obtained by the previously reported alkoxide route. Due to its low cost and ease of handling, the synthesis starting from V2O5 in particular provides an advantageous access to large quantities of the novel tubular nanomaterial.