摘要:

AbstractAs a part of fundamental study on the kinetics of electroceramics processing by wet chemical methods, barium titanate precursor gel was prepared using barium acetate and titanium tetra‐isopropapoxide as starting materials. Experimental results indicated that barium acetate was distributed uniformly in the gel matrix formed by hydrolysis and polymerization of titanium tetra‐isopropoxide. In the subsequent calcination of the gel, rapid formation of barium titanate was observed above 823 K, which resulted from the reaction between titania and barium carbonate or barium oxide(s). The dynamics of barium titanate formation under different heat‐up programs was successfully simulated based on a proposed reaction model that incorporates a specified reactive portion of barium acetate in the gel m

ISSN:0001-1541    

DOI:10.1002/aic.690431332

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractBa(Zr, Ti)O3[BZT] thin films were prepared for potential use as a decoupling capacitor for a multichip module (MCM). The crystal structure of BZT thin films on Pt(100)/MgO(100) and MgO(100) deposited from Ba(Zr0.2Ti0.8)O3powder targets has a perovskite structure and is strongly (100) oriented. The crystal structure of BZT thin films on Pt(111) coated substrates differ from that of Pt(100)/MgO(100) and MgO(100) substrates. The degree of preferred (100) orientation on Pt(111)/SiO2/Si increased with increasing deposition temperature. We obtained a maximum dielectric constant of 150 at 600°C deposition. The loss tangent, leakage current and temperature dependence of capacitance of these BZT thin films were very small

ISSN:0001-1541    

DOI:10.1002/aic.690431333

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractPiezoelectric ceramic/polymer composites, also known as piezocomposites, have been developed over the past two decades for electromechanical transducers to be used in both military and civilian applications. Recently, the thrust in these transducers is toward high operating frequencies, requiring fine‐scale (<200‐μm ceramic‐phase dimension) piezocomposites. Methods for processing these fine‐scale piezocomposites are discussed. Current capabilities, as well as strengths and weaknesses of each method, are compared. The fundamentals of medical imaging and the importance of spatial scale in composite performance are reviewed. Several processing methods demonstrated composites with fine‐scale ceramic phases (<50 μm), and others have shown the potential to form composites with a ceramic scale of

ISSN:0001-1541    

DOI:10.1002/aic.690431334

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractElemental depth profile examined using secondary‐ion mass spectroscopy and structural profile examined using grazing‐incident X‐ray diffractometry were applied to analyze the growth behavior of Pb1–xLax(ZryTi1–y)O3(PLZTO) and Pb1–xLaxTiO3(PLTO) thin films deposited on a Si substrate. When deposited under a suitably high substrate temperature, the chamber's oxygen pressure was observed to substantially influence the structure of the films. Low oxygen pressures (P O 2<0.01 mbar) deteriorate crystal structure without altering the composition of the films. Deposition of a buffer layer enhanced the formation kinetics of PLZTO and PLTO films. However, sufficiently thick SrTiO3(∼500 nm) layer was required to achieve this effect. Using (La0.5Sr0.5)CoO3/Pt materials as double‐layer electrodes not only prevented the film‐to‐substrate interaction, but resulted in preferentially oriented thin films. Ferroelectric properties of the films were thus greatly improved, with remanent polarization (Pr) around 14 ∼ 16 μC/cm2, coercive force (Ec) around 50 ∼ 60 kV/cm, and relative dielectric con

ISSN:0001-1541    

DOI:10.1002/aic.690431335

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe variation of crystal system and conduction behavior of perovskite superconductor, BaPb0.75Bi0.25O3‐δ, with oxygen deficiency was studied. The crystal system of BaPb0.75Bi0.25O3‐δchanged from orthorhombic through tetragonal to pseudo‐cubic as δ increases. The superconducting transition was observed in the specimens with the orthorhombic phase. Oxygen‐deficient specimens with tetragonal or pseudo‐cubic symmetry did not show a superconducting transition. The increase in electrical resistivity was also observed with an increase in δ. which suggested decrease of electron carrier mobility with the increase in δ. This effect of oxygen deficiency on conduction behavior of BaPb0.75Bi0.25O3‐δshowed contrast with those of the superconducting cuprates, in which carrier concentration is affected instead of carrier mobility. The difference in the effects of oxygen deficiency on conduction behavior could be attributed to the difference of crystal structure between BaPb0.75Bi0.25O3‐δand supe

ISSN:0001-1541    

DOI:10.1002/aic.690431336

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe atomic structure of amorphous silicon nitride fibers produced by two different methods is revealed using the technique of neutron scattering. Polymer‐derived fibers are found to contain excess crystalline silicon and disordered carbon, and fibers annealed in N2for 100 h contain a cristobalite phase that becomes amorphous under 200‐kV electron irradiation. Fibers grown from the gas phase, however, are shown to consist of almost pure amorphous Si3N4, with a small crystalline a‐Si3N4comp

ISSN:0001-1541    

DOI:10.1002/aic.690431337

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe preparation of LaNiO3, La4Ni3O10, La3Ni2O7‐δand La2NiO4via La‐methoxy‐ethanolato–Ni(acac)2precursor was investigated. From these precursors films, fibers and powders were prepared and heat treated to form LaNiO3at temperatures as low as 750°C with a heating time of 4 h. The formation of La4Ni3O10and La2NiO4was complete at 1,000°C, for 4 h, while monophasic La3Ni2O7required heating to 1,150°C, for 1 h. Pathways yielding various phases were also discussed briefly. The techniques used in this study are TGA, mass‐spectroscopy, SEM‐EDS, TEM‐EDS, powder‐XRD, and

ISSN:0001-1541    

DOI:10.1002/aic.690431338

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractPorous ceramics were fabricated by firing ceramic‐polymer composites prepared by casting dispersions containing cellulose acetate, water and colloidal ceramic particles (alumina and silica). Composite microstructures were determined by polymer phase separation. Polymer adsorption on the ceramic particles was necessary for the formation of controlled porosity in the composite and fired ceramic. Cellulose acetate adsorbed on alumina, but not silica particles. The microstructure of alumina‐cellulose acetate composites was characterized by unagglomerrated alumina particles in a polymer matrix; relatively large pores (pore diameter ∼ 15 μm) formed when the alumina concentration was low (<50 vol. % relative to the polymer in the dried composite), and smaller pores (pore diameter ∼2μm) developed at higher alumina contents. By contrast, silica‐cellulose acetate composites contained agglomerated silica particles and a large pore structure invariant to silica content. Firing of alumina‐cellulose acetate composites with ceramic contents greater than 40 vol. % resulted in crack‐free porous ceramics with pore structures comparable to the orig

ISSN:0001-1541    

DOI:10.1002/aic.690431339

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690431301

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY