Point, critical solution Curie

If the specific magnetization is plotted against temperature, it will be found that above a certain, fairly well-defined temperature, the induction drops nearly to zero. In other words, the substance loses its ferromagnetism and becomes merely paramagnetic. This temperature is known as the Curie point, Tc. The Curie point is a critical point, not unlike the melting point of an organic compound, and subject to somewhat the same changes in mixtures and solutions. 

Hydrothermal BaTiOs powders, particularly very fine powders (less than — 100 nm) prepared at lower temperatures, show some structural characteristics that are not observed for coarser powders prepared by solid-state reaction at higher temperatures. X-ray diffraction reveals a cubic structure that is normally observed only at temperatures above the ferroelectric Curie temperature of 125-130°C. The possible causes for the apparent cubic and nonferroelectric structure are not clear and have been discussed in detail elsewhere (74). They include the idea of a critical size for ferroelectricity and, particularly for powders prepared by precipitation from solution, the presence of a high concentration of point defects due to hydroyxl groups in the structure. 

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