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Very high and broad Curie maxima are observed in ceramic Ba(Til-,Zr,)03 mixed crystals, which are often used for the preparation of ceramic dielectrics. The ferroelectric-toparaelectric phase transition of ceramic Ba(Til-,Zry)Os was studied using dielectric measurements, quantitative DTA, X-ray diffraction, and determination of the remanent polarization. At higher Zr concentrations, it was found that ferroelectric and paraelectric phases coexist in a wide temperature region. Up toy =0.16, the phase transition remains first order. The diffuse character is promoted by the small energy difference between the ferroelectric and paraelectric phases appearing at higher Zr content. It can be best described by a normal distribution of Curie temperatures using the phenomenological theory of Devonshire and the Newton-Raphson mathematical approximation.

249As a final point, it is not considered likely that the present model will be of significance for pressureless sintering since the contribution of plastic flow mechanisms to densification under these conditions is believed to be limited.% IV. ConclusionsA dependence of the sample density on the logarithm of the processing time during hot-pressing can be interpreted as a consequence of the dependence of the stress multiplication factor on porosity under conditions where densification is by dislocation creep and where rapid mass transport allows pores to retain their equilibrium configurations.The activation energy of the densification rate in hot-pressing will differ from the activation energy of the corresponding diffusion coefficient when the slope of the density vs log time plot changes with the temperature, say as the result of a dependence of the dihedral angle on temperature. Changes of the stress multiplication factor with temperature must accordingly be incorporated in the calculations.Low values of the dihedral angle of the material and control of deformation by a mechanism with a high value of the stress exponent are favorable conditions according to the present analysis for the observation of this form of densification kinetics in hot-pressing.This interpretation of the semilogarithmic law of densification is supported by observations of the hot-pressing of high-purity MgO.

Hydrothermal powders of BaTiO 3 and (Ba,Ca)(Ti,Zr)O 3 contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100°-600°C. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800°C, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination.