摘要:

The La(Cr1‐xMnx)O3(x = 0 to 0.25) system exhibited a displacive phase transformation from an orthorhombic to a rhombohedral structure at temperatures ranging from about 256°C atx= 0 to 305°C atx= 0.25. The Rietveld method of X‐ray analysis was used to determine structural characteristics and to assay phase concentrations when multiple phases were present. Indications were that the Mn ions on the B site affected the transition temperature through an ionic size effect; i.e., Mn3+, with a larger ionic size than Cr3+, increased the transition temperature while the presence of the smaller Mn4+ions reduced it. A hysteresis was also observed with respect to the phase transformation as a function of temperature. The phase transformation was associated with a change in the rotation of the oxygen octahedra from an antiphase to an in‐phase tilt s

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04247.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The presence of TiC or TiN paritcles in an Al2O3matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed atT<900°C and at 900°C ≤T≤ 1100°C. At low temperatures (T<900°C), the oxidation follows a phase‐boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO2rutile crystals that subsequently grow and coalesce. When a continuous TiO2rutile layer is formed (T≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O2through a thick TiO2layer is proposed as t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04248.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

To check the development of nonsymmetry in bending creep tests an Al2O3ceramic containing a glass phase is investigated in interrupted creep tests. The symmetric part of the strain is measured by the deflection and the nonsymmetric part is obtained by length measurements between two Knoop indentations situated at the centerline of bending bars. It is observed that nonsymmetry in creep occurs not only in the secondary creep range but also in the primary range.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04249.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Shortcomings of the commonly used criteria for debonding of the fiber‐matrix interface are considered. A criterion which addresses these difficulties is proposed. With this criterion, it is possible to deduce something about the range of validity of Outwater and Murphy's1widely known approximate formula for debond initiatio

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04250.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Crack‐free SBN (SrxBa1‐xNb2O6) thin films have been prepared by a sol–gel method with metal alkoxides. A homogeneous and stable precursor solution was obtained from Sr and Ba metal and Nb(OEt)5in ethanol with a key additive of ethoxyethanol. SBN (wherex= 0.5) powder crystallized to orthorhombic phase at 700°C, and then transformed completely to tetragonal phase at 1200°C. The formation of tetragonal SBN was observed on sapphire (R) substrates at 700°C, whereas the tetragonal phase began to appear in the powders at 1000°C. SBN films with highly preferred orientation were successfully synthesized on MgO (100) substrates

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04251.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Perovskite potassium tantalate niobate (KTN) powders and thin films were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC2H5, Ta(OC2H5)5, and Nb(OC2H5)5in absolute ethanol. The precursor crystallized to pyrochlore at ∼ 650°C, and then to perovskite at ∼ 750°C, depending upon Ta:Nb ratio. H2O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04252.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Concurrent thermogravimetry (TG) and evolved‐gas analysis (EGA) were done for YBa2Cu3O7‐zand LaBa2Cu3‐O7‐zsuperconductors. The sample weights were monitored by thermobalance and the evolved O2and CO2species were monitored by quadruple mass spectrometer (QMS). No diffraction peak for the impurity phase containing a carbonate group was observed in the X‐ray diffraction patterns for these samples, but the release of CO2was detected by EGA. CO2gas began to evolve from YBa2Cu3O7‐zat 543°C and from LaBa2Cu3O7‐zat 692°C. Preparation of high‐quality YBa2Cu3O7‐zand LaBa2Cu3O7‐zsuperconductors is discussed on the basis of results of t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04253.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The complex impedance analysis technique was used to separate the grain‐boundary and grain impedances of ferrites of the system CoxFe3−xO4. All the samples, forx= 0.886, 0.960, 0.980, 0.995, 0.999, 1.005, 1.011, 1.021, 1.041, and 1.126, were fabricated by the traditional routine under the same conditions of preparation and sintering. The variations of both grain‐boundary and grain resistances with temperature were evaluated in the frequency range 100 Hz

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04254.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04255.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY