摘要:

The anomalously high permittivity in fine‐grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses involved are calculated. At these stresses levels, the reduced strain calculated on this model agrees well with X‐ray data for the fine‐grained material. The limitations and possible developments of the proposed model are dis

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04362.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The effect of two‐dimensional pressure on the permittivity of fine‐and coarse‐grained ceramic BaTiO3was investigated. It was shown that, unlike coarse‐grained (10μ or above) barium titanate, the permittivity of the fine‐grained (1μ mean) material increased with the increase in two‐dimensional compression perpendicular to the electrode, whereas for an intermediate grain size, the permittivity was almost independent of pressure. The apparent anomalous effect of the fine grain size on the pressure coefficient of permittivity was explained satisfactorily on the basis of an internal stress model using a modified Devonshire thermodyna

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04363.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.tb04364.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Various methods for the preparationof mixture for phase equilibrium studies are described. Especial attention has been paid to compositions which cannot be preserved in a glass structure.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04365.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.tb04366.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The anatase‐rutile phase transformation in Ar–Cl2atmosphere has been investigated by X‐ray powder diffraction, thermogravimetry, and scanning electron microscopy. At 950°C the phase transformation in Ar–Cl2atmosphere is about 300 times faster than in air. The growth of crystals of rutile from the vapor phase has been observed. We also determined that anatase powders with adsorbed chlorine rapidly rapidly transformed to rutile and underwent a color change from white to gray when they were heated in Ar at

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04367.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Based on a linear voltage ramp method, ultraslow dielectric relaxation of undoped BaTiO3ceramic has been carefully measured over the temperature range between − 180° and +120°C. Temperature dependence of the dielectric constant in the frequency range from 10−5to 10−1Hz can be obtained using Kramers–Kronig equations. Close to the Curie temperature, the dielectric constant increases so rapidly that the Curie peak is overwhelmed. Two kinds of relaxation processes were observed in this experiment. Ferroelectric domain and mobile charge are proposed to be responsible for the relaxation over the temperature range. With temperature increasing, Maxwell–Wagner relaxation associated with mobile charge gradually dominates. From relaxation time constants at various temperatures, relaxation activation energies about 0.06 and 0.09 eV are

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04368.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The development of a novel TiN‐reinforced silicon nitride/silicon oxynitride composite using an innovativein situTiN‐forming technique was investigated. Silicon powder compacts containing various amounts of TiO2(anatase structure) and sintering additives were nitrided under N2atmosphere and then further densified by hot pressing. The microstructure of the resultant composite was analyzed by X‐ray diffraction, scanning electron microscopy, and solid‐state nuclear magnetic resonance spectroscopy. The results of this study show that TiO2can be successfully converted to TiN during the nitridation of Si + TiO2mixture. The TiO2content affects not only the microstructure of the matrix but also the composition of the intergranular phase. The type and amount of sintering additives also show a significant effect on the microstructural development of the co

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04369.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A new type of barrier layer capacitor is described utilizing thin glass layers on highly conducting ceramics of barium plumbate and barium bismuth plumbate. The frequency dispersion of the apparent dielectric constant has been explained using a modified version of the Maxwell–Wagner model. These capacitors have a low temperature coefficient of capacitance and a high dispersion frequency in the megahertz range. Simple processing conditions together with low firing temperature make it possible to produce the barrier layer capacitors inexpensivel

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04370.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Ramp heating a glass batch with sulfate permits determination of the foaming temperature and maximum foam height as a function of sulfate addition. Experiments revealed that, in the soda–lime glass studied, foam was produced when the mass fraction of SO3in the glass was higher than 0.0027. With increasing sulfate content, the foaming temperature decreased and the maximum foam height increased until the mass fraction of SO3was 0.01. Further additions of sulfate had little effect on foaming temperature and decreased maximum foam height. The results are discussed in terms of sulfate solubility and nonequilibrium effect

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb04371.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY