Fabrication of Grain‐Oriented Bi2WO6 Ceramics

Kimura, Takeshi; Holmes, Marilyn; Newnham, R. E.

doi:10.1111/j.1151-2916.1982.tb10410.x

Cited by 50 publications

(29 citation statements)

References 10 publications

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“…A powder specimen with the chemical formula of La 2 GeO 5 was prepared from reagent-grade chemicals of La 2 O 3 (99.99%, Mitsuwa Chemicals Co. Ltd., Osaka, Japan) and GeO 2 (99.999%, Mitsuwa Chemicals Co. Ltd., Osaka, Japan). We precalcined the hygroscopic La 2 O 3 reagent at 1473 K for 10 min to remove La(OH) 3 and/or La 2 O 2 (CO 3 ) phases and obtained the proper amount of La 2 O 3 . The well-mixed chemical with the desired chemical composition was heated at 1873 K for 3 h, and then quenched in air.…”

Section: ■ Introductionmentioning

confidence: 99%

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]

Fukuda

Asaka

Hara

et al. 2015

Crystal Growth & Design

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We prepared the highly c*-axis-aligned polycrystalline lanthanum germanate oxyapatite, La 9.68 Ge 6 O 26.52 , by the reactive diffusion that occurs between a randomly grainoriented La 2 GeO 5 polycrystal and [GeO + 1/2O 2 ] gases at 1723 K in air. The resulting La 9.68 Ge 6 O 26.52 polycrystal was examined by optical microscopy, X-ray diffractometry, microRaman spectroscopy, and impedance spectroscopy. The crystal structure (space group P1) showed the appreciable positional disordering of 9 of the 24 O atoms, bonding to Ge atoms, in the unit cell. We have found an extra O site, with the occupation factor of 0.51, which was located close to one of the six Ge sites with the Ge−O distance of ∼0.198 nm. The Raman extra band at 649 cm −1 also suggested the existence of the five coordinate Ge atoms. The conductivity along the c* axis of oxide ions steadily increased from 6.3 × 10 −7 to 1.04 × 10 −2 S/cm as the temperature increased from 573 to 973 K. The activation energy of conduction was 1.2 eV. ■ INTRODUCTIONThe sintered polycrystalline materials (e.g., ceramics) that are formed by the conventional sintering methods normally possess a randomly grain-aligned structure. Such materials generally show isotropic mechanical (e.g., fracture toughness and bending strength) and physical (e.g., magnetic, pyroelectric, piezoelectric, and thermoelectric) properties. On the other hand, the ceramics with grain-aligned microtextures can demonstrate anisotropic properties. One of the most common texturing methods would be of the templated grain growth process, 1,2 and the others would comprise hot pressing, applying magnetic field, and utilizing centrifugal force. 3−5 However, these manufacturing processes are quite complicated and also the texture fraction of the grain-aligned ceramics is not necessarily satisfactory.Recently, the highly c-axis-oriented polycrystalline lanthanum silicate oxyapatite (LSO) has been successfully prepared by the solid-state reactive diffusion between La 2 SiO 5 and La 2 Si 2 O 7 . 6−11 The LSO is thermodynamically stable, in the binary system La 2 O 3 −SiO 2 , between the intermediate compounds of La 2 SiO 5 and La 2 Si 2 O 7 . The grain-aligned polycrystals of LSO have been readily formed as layers at the original contact boundaries of the La 2 SiO 5 /La 2 Si 2 O 7 diffusion couples after the heat treatment between 1773 and 1873 K for 5−100 h. The product LSO layer was separated by the original boundary into two adjacent regions. 6 The LSO crystals of the former La 2 SiO 5 region are grown by the reaction of La 2 SiO 5 with SiO 2 component, the latter of which is released from La 2 Si 2 O 7 . The LSO crystals of the former La 2 Si 2 O 7 region are generated by the loss of the SiO 2 component from La 2 Si 2 O 7 ; the contribution of in-coming La 2 O 3 flux, which crosses the original contact boundary from the La 2 SiO 5 region, is negligible. The chemical reaction processes of these unbalanced diffusion of SiO 2 component are described by 7,11

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Section: ■ Introductionmentioning

confidence: 99%

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]

Fukuda

Asaka

Hara

et al. 2015

Crystal Growth & Design

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“…5)7) Ceramic platelets, fibers or whiskers are used as seeded particles along with some additives to promote the anisotropic grain growth during sintering. 5) Alumina is commonly used due to its good mecha nical and thermal conductivity, optical properties, etc. There fore, many studies have been carried out on the production of textured alumina.…”

Section: Introductionmentioning

confidence: 99%

Textured Development of Feeble Magnetic Ceramics by Colloidal Processing Under High Magnetic Field

Sakka

Suzuki

2005

J. Ceram. Soc. Japan

227

141

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The controlled development of texture is one of the ways for effectively improving physical and mechanical properties. In this review paper, we introduce a new processing of textured ceramics with a feeble magnetic sus ceptibility by slip casting in a high magnetic field and subsequent heating. As an example of feeble magnetic ceramics, we demonstrate the fabrication of textured alumina in details. The susceptibility of diamagnetic aalu mina is very small, but the orientation energy of the alumina particle by a high magnetic field becomes greater than the thermal energy. aAlumina with a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field, the energy of crystal anisotropy becomes comparable to or greater than the energy of thermal motion. The degree of orientation depends on the processing factors, such as heating temperature, particle size, applied magnetic field, concentration of the suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other noncubic ceramics, such as TiO 2 , ZnO, SnO, hydrooxy apatite (HAP), AlN, SiC, Si 3 N 4 , etc.

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“…There are several fabrication methods of oriented ceramics: for example, templated grain growth (TGG), reactive TGG (RTGG), and hot forging [1,2,6,7]. However, these methods require anisotropic particles such as plate-like and needle-like particles.…”

Section: Introductionmentioning

confidence: 99%

Fabrication of (111)-oriented Tetragonal BaTiO3 Ceramics by an Electrophoretic Deposition in a High Magnetic Field

Kobayashi

Ueno

Nakashima

et al. 2015

Trans. Mat. Res. Soc. Japan

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(111)-oriented tetragonal barium titante (BaTiO 3 , BT) ceramics with the degree of (111) orientation of 100 % were fabricated by sintering (001)-oriented hexagonal BT accumulations prepared by a magnetic field assisted electrophoretic deposition (EPD) method. Apparent piezoelectric constant d 33 * value calculated from the slope of a unipolar strain vs. electric field curve of the (111)-oriented tetragonal BT ceramics was 597 pm/V, which was larger than that of randomly oriented ceramics (d 33 * = 460 pm/V). This enhancement was associated with an electric field induced phase transition.

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Fabrication of Grain‐Oriented Bi₂WO₆ Ceramics

Cited by 50 publications

References 10 publications

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]

Textured Development of Feeble Magnetic Ceramics by Colloidal Processing Under High Magnetic Field

Fabrication of (111)-oriented Tetragonal BaTiO<sub>3</sub> Ceramics by an Electrophoretic Deposition in a High Magnetic Field

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Fabrication of Grain‐Oriented Bi2WO6 Ceramics

Cited by 50 publications

References 10 publications

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La2GeO5 and Gases [GeO + 1/2O2]

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La2GeO5 and Gases [GeO + 1/2O2]

Textured Development of Feeble Magnetic Ceramics by Colloidal Processing Under High Magnetic Field

Fabrication of (111)-oriented Tetragonal BaTiO<sub>3</sub> Ceramics by an Electrophoretic Deposition in a High Magnetic Field

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Fabrication of Grain‐Oriented Bi₂WO₆ Ceramics

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]

Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La₂GeO₅ and Gases [GeO + 1/2O₂]