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  • 1
    Electronic Resource
    Electronic Resource
    Photoluminescence of Cerium-Doped α-SiAlON Materials (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Cerium-doped α-SiAlON (MxSi12−(m+n)Alm+nOnN16–n) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of α-Si3N4, AlN, and either (i) CeO2, (ii) CeO2+ Y-α-SiAlON seed, (iii) CeO2+ Y2O3, or (iv) CeO2+ CaO. Cerium-containing CeAl(Si6–zAlz)(N10–zOz) (JEM) phase, rather than Ce-α-SiAlON phase, forms in the sample with only CeO2, whereas a single-phase α-SiAlON generates in samples with dual doping (CeO2+ Y2O3 and CeO2+ CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; α-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and α-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5d band, because the coordination of Ce3+ in JEM and α-SiAlON is nitrogen enriched.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2004.tb07738.x
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  • 2
    Electronic Resource
    Electronic Resource
    Dielectric and ferroelectric properties of tetragonal tungsten bronze Sr2−xCaxNaNb5O15 (x=0.05–0.35) ceramics (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 835-837 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter reports the dielectric and ferroelectric properties of tungsten bronze Sr2−xCaxNaNb5O15 (SCNN, x=0.05–0.35) ceramics. Two dielectric anomalies and a diffuse ferroelectric transition behavior were appreciably observed in the compositions of x=0.05–0.25. The incorporation of smaller calcium cations into the crystal structure resulted in an increase in the Curie temperature, from 279 (x=0.05) to 297 (x=0.35), and a decrease in the permittivity, from 1353 to 543, at their respective Curie temperatures. Ferroelectricity was observed in the compositions with x=0.05–0.25, but absent in the compositions with x=0.30 and 0.35 at room temperature. The maximum spontaneous polarization Ps of 9.1 μC/cm2 and remanent polarization Pr of 3.0 μC/cm2 were achieved in the composition of x=0.15. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1446997
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructural Analysis of Liquid-Phase-Sintered β-Silicon Carbide (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The microstructures of fine-grained β-SiC materials with α-SiC seeds annealed either with or without uniaxial pressure at 1900°C for 4 h in an argon atmosphere were investigated using analytical electron microscopy and high-resolution electron microscopy (HREM). An applied annealing pressure can greatly retard phase transformation and grain growth. The material annealed with pressure consisted of fine grains with β-SiC as a major phase. In contrast, the microstructure in the material annealed without pressure consisted of elongated grains with half α-SiC. Energy-dispersive X-ray analysis showed no differences in the amount of segregation of aluminum and oxygen atoms at grain boundaries, but did show a significant difference in the segregation of yttrium atoms at grain boundaries along SiC grains for the two materials. The increased segregation of yttrium ions at grain boundaries caused by the applied pressure might be the reason for the retarded phase transformation and grain growth. HREM showed a thin secondary phase of 1 nm at the grain boundary interface for both materials. The development of a composite grain consisting of a mixture of β/α polytypes during annealing was a feature common to both materials. The possible mechanisms for grain growth and phase transformation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00107.x
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  • 4
    Electronic Resource
    Electronic Resource
    Phase Transformation and Texture in Hot-Forged or Annealed Liquid-Phase-Sintered Silicon Carbide Ceramics (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Starting from three powder mixtures of 80 vol% SiC (100α, 50α/50β, 100β) and 20 vol% YAG, liquid-phase-sintered silicon carbide ceramics were prepared by hot pressing at 1800°C for 1 h under 25 MPa, and then by hot forging or annealing at 1900°C for 4 h under an applied stress of 25 MPa in argon. The phase transformation and texture development in the as-hot-pressed, hot-forged, and annealed SiC ceramics were investigated via X-ray diffraction (XRD) and the pole figure measurements. The 6H → 4H polytypic transformation was observed in samples consisting of both α- and β-SiC phases when subjected to compressive deformation but absent in the case of annealing, suggesting the deformation-enhanced solubility of aluminum in SiC. Deformation was also found to enhance the 3C → 4H transformation in the sample containing entirely β-phase, which is due to the accelerated solution-precipitation process assisted by grain boundary sliding. The current study showed that the β- →α-phase transformation had little effect on texture development in SiC. Hot forging generally produced the strongest texture, with the calculated maximum of 2.2 times random in samples started with pure α-SiC phase. The mechanism for texture development was explained based on the microstructural observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00111.x
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal and Electrical Properties in Plasma-Activation-Sintered Silicon Carbide with Rare-Earth-Oxide Additives (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This study investigates the thermal and electrical properties of SiC ceramics with a combination of Y2O3 and rare-earth-oxide additions as sintering additives, by comparing four types of SiC starting powders varying in particle size and chemical composition. The powder mixtures were plasma-activation sintered to full densities and then annealed at high temperatures for grain growth. The thermal conductivity and electrical resistivity of the SiC ceramics were measured at room temperature by a laser-flash technique and a current–voltage method, respectively. The results indicate that the thermal conductivity and electrical resistivity of the SiC ceramics are dependent on the chemical composition and particle size of the starting powders. The thermal conductivities observed for all of the annealed materials with a rare-earth La2O3 sintering additive were 〉160 W·(m·K)−1, although low electrical resistivity was observed for all materials, in the range 3.4–450 Ω·cm. High thermal conductivity, up to 242 W·(m·K)−1, was achieved in an annealed material using a commercial 270 nm SiC starting powder.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb01033.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of β-to-α Phase Transformation on the Microstructural Development and Mechanical Properties of Fine-Grained Silicon Carbide Ceramics (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ultrafine β-SiC powders mixed with 7 wt% Al2O3, 2 wt% Y2O3, and 1.785 wt% CaCO3 were hot-pressed and subsequently annealed in either the absence or the presence of applied pressure. Because the β-SiC to α-SiC phase transformation is dependent on annealing conditions, the novel processing technique of annealing under pressure can control this phase transformation, and, hence, the microstructures and mechanical properties of fine-grained liquid-phase-sintered SiC ceramics. In comparison to annealing without pressure, the application of pressure during annealing greatly suppressed the phase transformation from β-SiC to α-SiC. Materials annealed with pressure exhibited a fine microstructure with equiaxed grains when the phase transformation from β-SiC to α-SiC was 〈30 vol%, whereas materials annealed without pressure developed microstructures with elongated grains when phase transformation was 〉30 vol%. These results suggested that the precise control of phase transformation in SiC ceramics and their mechanical properties could be achieved through annealing with or without pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00773.x
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  • 7
    Electronic Resource
    Electronic Resource
    Photoluminescence of Rare-Earth-Doped Ca-α-SiAlON Phosphors: Composition and Concentration Dependence (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Rare-earth-doped Ca-α-SiAlON phosphors, with the compositions of (Ca1−3/2xREx)m/2Si12−m−nAlm+nOnN16−n (RE=Ce, Sm, and Dy, 0.5≤m=2n≤3.0), were prepared by sintering at 1700°C for 2 h under 10 atm N2. The concentration of rare earths varied from 3 to 30 at.% with respect to Ca. The photoluminescence (PL) properties were investigated as functions of the composition of the host matrix (i.e., m) and the concentration of rare earths (i.e., x). The results show that the emission properties can be optimized by tailoring m and x. The Ce3+ luminescence originating from the 4f–5d interconfigurational transitions is greatly affected by the environment surrounding the Ce3+ ions, which differs from the Sm3+ or Dy3+ luminescence arising from the 4f–4f intraconfigurational transitions. X-ray diffraction and scanning electron microscopy were used to explain the composition and concentration dependence of PL properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00532.x
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation and Luminescence Spectra of Calcium- and Rare-Earth (R = Eu, Tb, and Pr)-Codoped α-SiAlON Ceramics (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, we report the photoluminescence (PL) spectra of europium-, terbium-, and praseodymium-doped Ca-α-SiAlON ceramics. The highly dense ceramics were prepared by hot pressing at 1750°C for 1 h under 20 MPa in a nitrogen atmosphere. Europium-doped Ca-α-SiAlON displayed a single broad emission band peaking at λ= 550–590 nm depending on the europium concentration. The emission bands in the spectra of europium-doped Ca-α-SiAlONs were assigned to the allowed transition of Eu2+ from the lowest crystal field component of 4f65d to 8S7/2 (4f7) ground-state level. The emission spectra of terbium- and praseodymium-doped Ca-α-SiAlON ceramics both consisted of several sharp lines, which were attributed to the 5D4→7Fj (j= 3, 4, 5, 6) transitions of Tb3+ and 3P0→3Hj (j= 3, 4, 5) transitions of Pr3+, respectively. In particular, the terbium-doped α-SiAlON ceramics showed a strong green emission among these phosphors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00250.x
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  • 9
    Electronic Resource
    Electronic Resource
    Spark Plasma Sintering of Tungsten Bronze Sr2−xCaxNaNb5O15 (x= 0.1) Piezoelectric Ceramics: I, Processing and Microstructure (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Tungsten bronze Sr2−xCaxNaNb5O15 (SCNN, x= 0.1) piezoelectric ceramics were prepared by a novel super-fast sintering technique, i.e., spark plasma sintering (SPS). Sintering was conducted at temperatures ranging from 1000° to 1200°C under vacuum under 35 MPa. The heating rate varied from 30° to 300°C/min and the soaking time was in the range of 5 to 60 min. The microstructure and the phase identification were analyzed via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The density of the sintered ceramics increased with an increase in sintering temperature as well as in heating rate. Materials with a near-theoretical density could be attained by sintering at 1200°C for 5 min with a heating rate of 300°C/min, exhibiting a homogeneous and fine-grained microstructure (grain size about 2.7 μm) and a uniform translucency. A tetragonal tungsten bronze phase was identified in ceramics sintered at temperatures above 1200°C, whereas the tungsten bronze phase transformed to a SrNb2O6-type phase in the materials sintered at temperatures below 1200°C. XRD patterns demonstrated a preferred crystallographic orientation of the SCNN grains with their c-axes perpendicular to the pressing direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00520.x
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  • 10
    Electronic Resource
    Electronic Resource
    Spark Plasma Sintering of Tungsten Bronze Sr2−xCaxNaNb5O15 (x= 0.1) Piezoelectric Ceramics: II, Electrical Properties (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sr2−xCaxNaNb5O15 (SCNN, x= 0.1) piezoelectric ceramics with tetragonal tungsten bonze structure were successfully produced by spark plasma sintering. Part I of this study presented the sintering of these highly dense ceramics. The current work investigates their electrical (dielectric, ferroelectric, and piezoelectric) properties and relates them to the sintering parameters (temperature, heating rate, and soaking time) and crystallographic orientation. The results show that the electrical properties of SCNN are enhanced with increasing heating rate and soaking time. Dielectric study reveals a less pronounced diffuse phase transition of SCNN. Anisotropic electrical properties were observed as a result of the preferred crystallographic orientation in the sintered ceramics. The samples sintered at 1200°C for 30 min exhibited the highest electrical properties, and showed the following piezoelectric properties when poled across the direction perpendicular to the pressing direction: electromechanical planar and thickness coupling coefficients of kp= 9.5% and kt= 39.6%, and piezoelectric constant of d33= 121 pC/N (∼45% of the single-crystal value).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00521.x
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