PREPARATION AND ANALYSIS OF ALUMINATE SODALITE CERAMICS FROM SOLUTIONSPRAY-DRIED PRECURSORS

Aluminate sodalite ceramics, (Sr-8(Al12O24)(CrO4)(2)) - SACR, have bee n prepared from solution spray-dried precursors. The spray drying of a mixed aqueous nitrate solution gave an anhydrous powder which was the rmally decomposed in air at 1350 degrees C to give a crystalline SACR powder with a median volume diameter of 4-6 mu m. The SACR powder was dry pressed and sintered to >90% density. The yellow SACR powder showe d two phase transitions between 10 and 45 degrees C with a 25 degrees intermediate phase region indicative of a low defect concentration in the crystalline structure. A colour change observed in the sintered ce ramic (changing to a mixed green/yellow) and a narrowing of the phase transition region (15-40 degrees C) are discussed. Dielectric measurem ents were consistent with the presence of two extrinsic ferroelectric transitions at 17 and 35 degrees C.