Formation Mechanism of Impure Phases and Crystallinity Investigation of YAG Powders Synthesized via the Co-precipitation Method

Abstract

We investigated the impure phase problem and summarized its two formation mechanisms of YAG powders synthesized via the co-precipitation method. The ions loss problem caused by high concentration reaction solution in the titration process was emphatically studied, and the corresponding thermodynamic explanation was carried out. In addition, influence of powder crystallinity and its new qualitative and quantitative standards were studied. One reason of impure phase is the local nonuniform mixture of Y and Al elements in precursor, which easily causes intermediate phases during calcination and difficulty of high pure powders at low temperatures. The other reason is the precipitation dissolution during titration and then the Y³⁺/Al³⁺ loss, caused by high concentration of reaction solution. The powder crystallinity can be promoted by increasing calcination temperature or holding time of precursor. Besides the routine XRD method, the TEM-EDX method should be also introduced to directly determine the quality of crystallinity.

Keywords

transparent ceramics / phase transition / crystallinity / co-precipitation / activity coefficient