Preparation and analysis of aluminate sodalite ceramics from solution spray-dried precursors

Abstract

Aluminate sodalite ceramics, (Sre,(Al12024)(CrO4)2) -SACR, have been prepared from solution spray-dried precursors. The spray drying of a mixed aqueous nitrate solution gave an anhydrous powder which was thermally decomposed in air at 1350~ to give a crystalline SACR powder with a median volume diameter of 4-6 lam. The SACR powder was dry pressed and sintered to >90% density. The yellow SACR powder showed two phase transitions between 10 and 45~ with a 25 ~ intermediate phase region indicative of a low defect concentration in the crystalline structure. A colour change observed in the sintered ceramic (changing to a mixed green/yellow) and a narrowing of the phase transition region (15-40~ are discussed. Dielectric measurements were consistent with the presence of two extrinsic ferroelectric transitions at 17 and 35~