Kazuyuki Kakegawa

A compositional fluctuation and properties of Pb(Zr, Ti)O3

Abstract Structure and properties of piezoelectric materials of composition Pb(ZrxTi1−x)O3 near the morphotropic phase boundary between tetragonal and rhombohedral phases are studied. When these materials were prepared by a new “wet-dry combination technique”, no coexistence of these two phases was found in any range of compositions. This fact is in contrast with the case of Pb(ZrxTi1−x)O3 prepared by an ordinary dry method. The coexistence behavior is interpreted in terms of compositional fluctuation, on the basis of which various properties of the materials are explained.

Defect structure and oxygen diffusion in undoped and La‐doped polycrystalline barium titanate

Oxygen diffusion coefficients in undoped and La‐doped polycrystalline barium titanate were measured at an ambient oxygen pressure of about 40 Torr over the temperature range 770–1430 °C by a solid–gas exchange technique of O18. The undoped material was characterized only by an extrinsic region with a high diffusivity, whereas two types of La‐doped materials displayed an intrinsic region with E?100 kcal/mol in addition to a common extrinsic region of a very low level of diffusivity. New ideas concerning defect equilibria for the doped materials are proposed for the extrinsic and intrinsic region. In addition, the origin of semiconducting behavior characteristic of the doped specimens is interpreted on a basis of new idea.

Effect of alkali metal hydroxide on formation processes of zinc oxide crystallites from aqueous solutions containing Zn(OH)42− ions

Aqueous solutions containing Zn(OH)42− ions were prepared by adding 50 ml of 1.5 mol l−1 aqueous alkali metal hydroxide (MOH: M = Li, Na, K, Cs) to 50 ml of 0.1 mol l−1 aqueous zinc nitrate hydrate (Zn(NO3)2·6H2O). Zinc oxide (ZnO) crystallites were obtained by heating aqueous solutions containing Zn(OH)42− ions at ≥348 or 368 K for 3 h. The morphology depended on both of the heating temperature of the Zn(OH)42− aqueous solution and the alkali metal hydroxide used to obtain Zn(OH)42− ions. According to the result of the kinetics of the zinc oxide formation, it was shown that the decomposition of Zn(OH)42− ions on the zinc oxide surface was the rate determining step when NaOH, KOH and CsOH were used to obtain Zn(OH)42− ions. When LiOH was used to obtain Zn(OH)42− ions, the rate determining step was the nucleation of zinc oxide and/or the adsorption of Zn(OH)42− ions.

Eutectic Al2O3-GdAlO3 composite consolidated by combined rapid quenching and spark plasma sintering technique

Abstract A mixture of Al2O3 and GdAlO3 was melted and rapid quenched to produce an amorphous film. Dense eutectic composites were consolidated from ground amorphous powder using both conventional and spark plasma sintering (SPS). Conventional sintering at temperatures above 1600°C for 24 h was required for complete sintering. However, using SPS complete sintering could be obtained at temperatures between 1300 and 1500°C with no soaking. The SPS technique could consolidate ultrafine eutectic structure from rapid quenched amorphous material, whilst conventional sintering was not successful owing to grain growth. A combination of rapid quenching and SPS resulted in an ultrafine eutectic Al2O3–GdAlO3 structure.

Origin of semiconductng behavior in rare-earth-doped barium titanate

Abstract New explanations of the origin of semiconduction and a peculiar characteristics of resistivity vs dopant concentration in rare-earth-doped barium titanate are presented on a basis of the combined data of cation vacancy concentration, resistivity, and oxygen diffusion coefficient of the material. A limited amount of rare-earth doping into barium titanate results in the introduction of Ba-site vacancies as well as Ti-site vacancies in the lattice. The existence of Ba-site vacancies profoundly alters the chemical bonding nature of the host lattice and thereby causes some loss of oxygen as well as the formation of oxygen vacancies with captured electrons in the lattice on firing the material at elevated temperatures, the latter giving rise to n -type semiconduction. A sudden fall in conductivity for a higher rare-earth concentration occurs in accordance with the number of Ba-site vacancies being zero.

Preparation and Nonstoichiometric Property of wide Compositional Fe(III)-doped TiO 2 (anatase)

Fe(III)-doped TiO 2 (anatase) was prepared by the oxidation of Fe x TiS 2 . Two calcination methods were used to oxidize Fe x TiS 2 . In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO 2 (anatase), forming Fe(III)-doped TiO 2 (anatase), in the composition range of 0 ⩽ Fe/Ti ⩽ 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of Fe x TiS 2 . The electronic property and the valence stage of the Fe(III)-doped TiO 2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO 2 (anatase) was decreased by the Fe(III) doping.

Spark Plasma Sintering of Transparent PbZrO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 Ceramics

A new method of preparing transparent PbZrO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 (PZ-PT-PZN) ceramics was proposed. This is a multiprocess in which the mixtures of calcined powders were spark plasma sintered for 10 min and then thermally treated for 1 h. Although the sintering time was very short, the densities of the samples prepared by this method were nearly theoretical and the samples were optically transparent. The transparent PZ-PT-PZN ceramics could be promising candidates for applications to areas such as electrooptics and pyrooptics.

Synthesis of rutile and anatase TiO2 nanoparticles from Ti-peroxy compound aqueous solution with polyols

Ti-peroxy compound was synthesized from Ti(O-iPr) 4 and H 2 O 2 . Anatase and rutile TiO 2 nanoparticles were prepared by heating the Ti-peroxy compound diluted with a polyol aqueous solution at 368 K for 24 h. In this research, ethylene glycol, glycerin, erythritol, and D-mannitol were used as polyols in the diluting solution. The ratio of anatase/rutile of the TiO 2 obtained depended on the polyol concentration in the diluting solution. Furthermore, the polyol concentration at which single-phase anatase could be obtained was lowest when the number of OH groups in the polyol molecule was the highest. With increasing polyol concentration, the obtained TiO 2 nanoparticles showed increasing specific surface area and decreasing particle size.

Characterization of CeO 2 Fine Particles Prepared by the Homogeneous Precipitation Method with a Mixed Solutionof Ethylene Glycol and Polyethylene Glycol

Cerium oxide (CeO 2 ) nanoparticles were obtained by heating a polyethylene glycol (PEG) solution of cerium nitrate hydrate [Ce(NO 3 ) 3 6H 2 O] at 383 K for 3 h. When the PEG, whose molecular weight was 20,000, was used for the preparation, the monodispersed CeO 2 , whose particle size was about 102 nm, was obtained. When the mixture of PEG20,000 and ethylene glycol (EG) was used to prepare the PEG solution of cerium nitrate hydrate, the average particle size increased from 102 nm to 660 nm with an increase in the EG content of the solution. The pore structure in the obtained CeO 2 particles also depended on the weight ratio between EG and PEG20,000.

Defect ferroelectrics of type Pb1−xTiO3−x

Abstract A series of new ferroelectric substances of type Pb1−xTiO3−x or Pb 1−x Na y TiO 3−x+( y 2 ) with perovskite-type structure was prepared by simple solid state reaction among powdered mixtures of PbO, TiO2, and in a several cases, Na2CO3, with TiO2 in an excess. The defect materials are characterized in terms of inhomogeneously distributed vacancies, □pb and □O at the respective equivalent lattice positions. Their ferroelectric properties are discussed in relation to those of the same type of materials precipitated aqueously and followed by firing at elevated temperatures