Cracks in transparent La-doped yttria ceramics and the formation mechanism

Crack is a common phenomenon in ceramics, which often extends and breaks the ceramic bodies. In the present study, however, cracks formed a network inside some transparent La-doped yttria ceramics, while didn't break the samples. The reason was studied by investigating the mixed La2O3 and Y2O3 powders using SEM, TG-TDA BET, and XRD. The crack network is attributed to the volume effects of La(OH)3 dehydration and solid state reaction of oxides, both proceed gradually instead of suddenly along with temperature increasing during heating procedure of sintering. Hence, the corresponding stresses made cracks inside La-doped yttria ceramics without broken the bodies. The cracks could be eliminated by increasing the powder calcination temperature to reduce the above volume effects.