STRUCTURAL, FERROELECTRIC AND PYROELECTRIC PROPERTIES OF NONSTOICHIOMETRIC CERAMICS BASED ON BAAL2O4

The density and the ferroelectric and pyroelectric properties of ceram ics derived from BaAl2O4 have been investigated. The X-ray diffraction patterns and the variation of the density are consistent with the pre sence at 300 K of nonstoichiometric materials in the 44.4-50.0 mol% Ba O range. They appear to be ferrielectric like BaAl2O4. The Curie tempe rature varies from 396 K (50%BaO) to 275 K (44.4%BaO) due to the compo sition change of the solid solution. The value of the spontaneous pola rization, P(s), is relatively small and shows anomalous behavior: the thermal variation presents a maximum but there is no structural change . The unit cell volume increases with decreasing BaO content. A substi tution mechanism based on the replacement of two Ba2+ for an [Al-O-Al] 4+ link, and a model accounting for the ferrielectricity are proposed.