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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    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: A commercial TiO2-excess BaTiO3 powder has been sintered and its microstructure analyzed for crystallographic facetting via both scanning and transmission electron microscopy (SEM and TEM). Facetted grain surfaces are developed initially from {111} at a low temperature of 1215°C, which are then altered to {111} and {100} at 1290°C in the presence of a grain-boundary liquid phase. The grain shape is also modified correspondingly from platelike to polygonal. Facetting of the intragranularly located residual pores in BaTiO3 along the {141} planes further develops on the (quasi-)equilibrium shape after annealing at 1400°C for 100 h from the initially well-characterized {111}, {110}, and {100} in as-sintered samples sintered at the same temperature for 10 h. The Wulff plots derived from the residual pores in as-sintered and annealed samples are constructed for the 〈011〉 zone. Microstructural analysis also suggests that the shape of grains and intragranular residual pores is modified progressively upon annealing. The initial solid–vapor surface energy has become less anisotropic crystallographically. Abnormal grain growth in relation to the surface energy anisotropy is discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    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: Two types of superlattice reflections have been observed in pressureless-sintered Pb(Fe2/3W1/3)O3 perovskite ceramics from selected-area electron diffraction patterns (SADPs). The presence of commensurate superlattice reflections of the {1/2 1/2 1/2} type found in as-sintered samples persisted after prolonged postsintering annealing at 800°C for 300 h. These reflections, conventionally termed the F-spots, represent the existence of the nanoscale cation-ordered domains of cubic perovskite Pb1−x(Fe1/2W1/2)O3. However, the satellite-type incommensurate superlattice reflections, appearing as sideband spots to the fundamental reflections and occurring only along 〈111〉, 〈110〉, and 〈100〉, have gradually reduced their intensities and finally disappeared on postsintering annealing at 800°C. Observations via transmission electron microscopy (TEM) suggested that the “black dots” revealed in bright-field (BF) images have given rise to the incommensurate superlattice sideband spots. These dots of ∼5–10 nm are in fact a different type of nanocrystalline domain whose structure (and chemical composition) differs from those of the disordered Pb(Fe2/3W1/3)O3 matrix and the ordered nanoscale Pb1−x(Fe1/2W1/2)O3 domains. The nanocrystalline precipitates containing the paracrystalline phase are pyrochlore (Pb2(Fe,W)O6.5) formed during powder preparation via the solid-state mixed-oxide route. They become dispersed in the Pb(Fe2/3W1/3)O3 perovskite matrix grain and have also undergone phase transformation to perovskite progressively during sintering and postsintering annealing. It is suggested that the nanocrystalline pyrochlore precipitates are metastable and disappear when chemical composition within the perovskite grains becomes homogenized from solid-state diffusion on postsintering annealing.
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  • 3
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    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 dependence of flexural strength on crystalline phase content, residual porosity, and sintering temperature has been investigated for ceramic cores based on a mixture of fused silica and zircon. The rule of binary particle mixture, adopted for three particle sizes of fused silica, predicts a critical weight fraction of fine (zircon) particles of 46.9 wt% for the best packing. However, the optimal composition of a 37.8 wt% zircon–fused silica mixture for the flexural strength of ceramic cores found experimentally is lower in zircon content. The content of α-cristobalite +α-quartz crystallized from infilling silica sols exceeds ∼3 wt% when the strength decreases from ∼10 MPa to ∼6 MPa in samples sintered at 899–927°C. The degradation is ascribed to microcracking and the loss of coherency between the fused silica grains and the infilled silica due to β- →α-phase transformation on cooling and differential densification during sintering.
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  • 4
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    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: Lead zirconate titanate (Pb(Zr,Ti)O3, PZT) thin films were grown on silicon 〈100〉 substrate by aerosol plasma deposition (APD) using solid-state-reacted powder containing donor oxide Nb2O5 when keeping the substrate at room temperature and 200°C. Crystalline phases of the deposited films have been analyzed via X-ray diffractometry (XRD), and microstructure via scanning and transmission electron microscopy (SEM and TEM). Cross-sectional TEM revealed that the microstructure comprised several layers including the deposited PZT film and the platinum-electrode-and-titanium-buffered layers on SiO2–Si substrate. The Pt-electrode layer contained (111)Pt twinned columnar grains with a slight misorientation and forming low-angle grain boundaries among them. The PZT layer contained randomly oriented grains embedded in an amorphous matrix. Some of the PZT grains, oriented with the zone axis Z= [[Twomacr]11]PZT parallel to Z= [111]Pt, were grown epitaxially on the Pt layer by sharing the (111)PZT plane with the (111)Pt twinned columnar Pt crystals. However, the existence of such an orientation relationship was confined to several nanosize grains at and near the PZT-Pt interface, and no gross film texture has been developed. An amorphous grain boundary phase, generated by pressure-induced amorphisation (PIA) in the solid state, was identified by high-resolution imaging. Its presence is taken to account for the densification of the PZT thin films via a sintering mechanism involving an amorphous phase on deposition at 25° and 200°C.
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  • 5
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    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: Pressureless-sintered TiO2-excess BaTiO3 (BT) ceramic doped with Na2O (as an acceptor oxide) has been investigated for the inhibition of platelike (111) twin grains and the associated microstructure development. Solid-state reaction between the Na2O dopant and the excess TiO2 of the nonstoichiometric BaTiO3 powder during sintering has resulted in the formation of orthorhombic Na4TiO4(N4T) at temperatures of ≤1215°C. Enhanced densification is due to a liquid-phase sintering mechanism, where the liquid eutectic is generated by reacting the excess TiO2 and the trace impurities of SiO2 and Al2O3 with the Na2O dopant. Suppression of the abnormally large, platelike grains occurs at a critical acceptor concentration of ∼0.50 mol% Na2O when sintering is conducted at 1215°C. The inhibition mechanism is associated with the secondary phases, whose formation gradually modifies the initially TiO2-excess powder toward the stoichiometric composition. The corresponding sintered microstructure is analyzed using both scanning and transmission electron microscopy. The second-phase precipitates of Na4TiO4, which are located intragranularly and intergranularly in the tetragonal BaTiO3 matrix grains, exhibit the following crystallographic orientation relationships: [110]BT// [100]N4T, (1〈inlineGraphic alt="inline image" href="urn:x-wiley:00027820:JACE2155:JACE_2155_mu1" location="equation/JACE_2155_mu1.gif" extraInfo="missing"/〉1)BT// (010)N4T, and (112)BT// (001)N4T.
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  • 6
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    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: Pressureless sintering studies have been conducted for excess Al2O3, stoichiometric, and excess MgO compositions of MgAl2O4 at 1500-1625°C. Initial powders of various compositions are prepared by solid-state reaction of MgO and Al2O3. A Brouwer defect equilibrium diagram is constructed that assumes intrinsic defects of the Schottky type. The densification rate derived from sintering kinetics is compared with the compositions investigated when the concentration is converted to the activity of the two oxide components in MgAl2O4. The grain-size exponent of p similar/congruent 3 suggests that densification takes place by a lattice-diffusion mechanism in the solid state. Determined activation enthalpies of 489-505 kJmol-1 are close to those obtained from oxygen self-diffusion derived in previous sintering studies. It is, therefore, proposed that oxygen lattice diffusion through vacancies is the rate-controlling mechanism for the sintering of nonstoichiometric MgAl2O4 compositions. The discrepancy between densification-rate ratios in experimental results and oxygen vacancy concentration in the Brouwer diagram is accounted for by the defect associates formed in the nonstoichiometric compositions.
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  • 7
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    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: Sintering of magnesium aluminate spinel of the MgO-excess, stoichiometric, and Al2O3-excess compositions has been investigated under vacuum and in air for the effect of low oxygen partial pressures. Densification enhancement of the surface layer is due to MgO evaporation which generates oxygen vacancies in the host crystal lattice. Regions of different grain sizes are observed from samples sintered under both conditions. Microstructural features of pairwise breakup of particle chains representing differential sintering are characteristic of the less-densified sample interior. The densification improved initially and yet was retarded in the intermediate sintering stage when the density exceeded 75% with vacuum-sintering owing to MgO evaporation.
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  • 8
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    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: Low-temperature co-fired ceramics (LTCCs) that are composed of a RuO2-based resistor and a cordierite–glass substrate have been sintered at temperatures of 850° and 900°C. The microstructure of the resistor/substrate interface has been investigated using scanning and transmission electron microscopy, and its correlation to the overall resistance has been discussed. X-ray diffractometry has revealed that lead ruthenate pyrochlore (Pb2Ru2O6.5) in peak-fired thick-film resistors (TFRs) disappears and the co-fired samples contain only RuO2 in the resistor film when sintered at 900°C. The overall resistance of the LTCC resistors is increased by a factor of ∼3 when temperature is increased from 850°C to 900°C. The cordierite–glass composition of the initial substrate reacts with glass in the resistor film. The greatly extended layer of the resistor/substrate interface that contains the conductor particles is either broad or diffuse, which contrasts the abrupt interface that often is observed in conventional TFRs. This layer contains predominantly faceted platelike crystals of anorthite, in addition to other phases (such as diopside, sapphirine, and cristobalite) that apparently crystallize during co-firing as vitrification and chemical reactions between glass compositions of the substrate and the resistor occur. The increase in the resistance of the LTCC resistors is attributed to the interruption of the conducting path by platelike anorthite crystals that are produced in the resistor/substrate interface when subjected to co-firing.
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  • 9
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    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: Planar defects in the metastably retained h-BaTiO3 exhibiting α-fringe pattern have been characterized via transmission electron microscopy (TEM). The eligible fault vectors were determined by adopting the invisibility criteria of 2πg·R = 0 or 2nπ augmented by high-resolution imaging. Three stacking faults, F1, F2, and F3, of the extrinsic nature have been fully analyzed. The eligible fault vectors for faults F1 and F3 contained a basal component respectively of ⅓[0001] and ⅙[0001] and a common prismatic component of ⅓〈10[1-macr]0〉. However, only three of the 〈10[1-macr]0〉 vectors are the eligible prismatic component for the fault vectors RF1=⅓[0[1-macr]11], ⅓[10[1-macr]1], and ⅓[[1-macr]101], and RF3=⅙[02[2-macr]1], ⅙[2[2-macr]01], and ⅙[[2-macr]021] that have fulfilled the invisibility criteria. On the other hand, all fault vectors RF21=⅙〈[4-macr]223〉 for fault F2, containing six vectors of the 〈[2-macr]110〉 family, is eligible. Unlike the faults of πRF=⅙〈[2-macr]203〉 found in the D019 intermetallics of Ni3Sn and Co3W, neither fault F1 nor F3 is the π-rotation type. Fault F2, however, is a π-rotation fault since a 60°-rotation clockwise about [0001] has produced another eligible fault vector.
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