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Starting from gelatinous aluminum chloride hydroxide, the transformation process toward α‐Al2O3 was examined using 27Al NMR, both in the liquid and solid states, as a main analytical tool. By increasing the hydrolysis ratio (h, defined as [OH−]/[Al3+]) of the starting aqueous precursor up to h = 2.5, the transition temperature to the final product, α‐Al2O3, decreased to as low as 500°C. In this case, the structural change from amorphous alumina to α‐Al2O3 took place without intermediate transition Al2O3 phases. Examining the process of networking during the transition from aqueous sol–through the state of xerogel–to final anhydrous oxide by nuclear magnetic resonance (NMR) revealed the presence of highly polymeric species mainly ascribed to δ‐[Al2O8Al28(OH)56(H2O)24]18+ (δ‐Al30). δ‐Al30 species were found in the solution phase and became predominant after drying. We conclude that the lower temperature synthesis of α‐Al2O3 became possible due to preformation of polymerized AlO6 construction units in the precursor, reducing the energy barrier for the nucleation of the final α‐Al2O3 phase. Low temperature synthesis of α?Al2O3 from gelatinous aluminum chloride hydroxide containing highly polymeric Al species tracked by 27Al NMR. [ABSTRACT FROM AUTHOR]

Phase-pure K0.5Na0.5NbO3 ( KNN) fine powders were synthesized via a solid-state route from a homogeneous solid mixture. A colloidal dispersion comprising a mixed ethanol solution of potassium and sodium acetates and Nb2 O5 fine particles was attrition milled and dried carefully to avoid water absorption. Two-step calcination in air at 450°C and 625°C, each for 3 h, resulted in the phase-pure KNN powders. The volume-based median diameter of the final product was ca. 0.8 μm. Starting from the same precursors without dissolving the acetates, the phase-pure KNN was never achieved even when the two calcination temperatures were increased to 550°C and 700°C, in spite of the same milling conditions. Key issues of eliminating second phases were (i) starting from a wet-milled mixture with a single solution containing both of the A-site species, and (ii) repeated wet milling of the reaction mixture to disintegrate reaction-induced agglomerates. These enabled rapid nuclei growth from chemically interacted precursor prior to calcination, and short diffusion path due to repeated deagglomeration, excluding formation of off-stoichiometric second phases. All these items were confirmed by different analytical tools, among others, thermo-gravimetry and differential thermal analysis (TG-DTA), particle size analyses, and XPS at various reaction stages. On the heating stage microscope, a shrinkage onset was observed at 850°C, that is, 150 K lower than that of conventionally prepared KNN, that is, via a solid-state synthesis from carbonates by a two-step calcination at 800°C and 750°C, for 4 h each. No second phase was observed after sintering up to 1100°C. [ABSTRACT FROM AUTHOR]

A novel synthetic method of fine particles of highly pure Li4Ti5O12 with the smallest possible particle size was proposed. A stoichiometric mixture of CH3COOLi·2H2O and anatase fine particles of ca. 50 nm was calcined at 773 K to obtain an intermediate, comprising Li2TiO3 and unreacted titania. The intermediate was then intensively milled by a planetary ball mill for 1 h. After adding an amino acid, glycine, alanine (ALA), orl-phenylalanine (PHE), the mixture was further milled under a milder condition for another 3 h and subjected to a second calcination at 973 K for 1 h to obtain Li4Ti5O12 with a phase purity above 97%. When we used ALA or PHE as an additive, the microscopically determined average particle size of Li4Ti5O12 was 70±10 nm. The mechanisms and significance of the present two-step calcination with mechanical activation and addition of an amino acid to the intermediate were discussed in terms of the topotactic nature of transformation between the two layer-structured species: Li2TiO3 and Li4Ti5O12. [ABSTRACT FROM AUTHOR]

Well-dispersed barium titanate (BaTiO3; BT) with an average primary particle size <200 nm and lattice tetragonality 1.010, being very close to that of a BT single crystal, was obtained via a solid-state route with the aid of preliminary dry mechanical processing. The latter treatment not only activates the starting mixture but also decreases the particle sizes of individual ingredients and increases the homogeneity. All these favor to suppress grain growth of the product BT due to increasing nucleation site density, easing the nucleation at the given nucleation site, and decreasing the diffusion paths. These were confirmed by (i) microscopy and particle size analysis to observe downsizing of individual particulates without causing agglomeration; (ii) electron probe microanalysis to reveal increase in the homogeneity in a few micrometer regime; and (iii) X-ray photoelectron spectroscopy to reveal mechanochemical effects across the solid–solid boundary of dissimilar particles. [ABSTRACT FROM AUTHOR]

Reports on the synthesis of phase-pure Pb(Zn[sub x]Mg[sub 1-x])[sub 1/3]Nb[sub 2/3]O[sub 3] up to x = 0.7 from a single mixture. Application of a soft-mechanochemical route; Decrease of perovskite with respect to total crystalline phase with increasing temperature of subsequent heating; Near linear increase of Curie temperature with increase of value of x.