Defects in the grain interiors of 3 mol%yttria-stabilized tetragonal zirconia polycrystal ceramics with 0.25 wt%alumina

The presence of high-density defects is rarely observed in bulk 3 mol%yttria-stabilized tetragonal zirconia polycrystal(3Y-TZP)ceramics obtained through conventional pressureless sintering.In the present work,fine-grained dense 147 nm 3Y-TZP ceramics were prepared by pressureless sintering of commercial 0.25 wt%alumina-doped zirconia powders at 1300℃.A novel discovery was reported in which large amounts of defects were present in the grain interiors of the sample.The phenomenon was further examined using three types of powder samples,and the reasons for defect formation were investigated by microstructural characterization using high-resolution transmission electron microscopy(HRTEM)analysis and Rietveld refinement.The results confirmed the essential dependence of the defect formation on the alumina addition.The authors attributed the defect formation to the significant difference in ionic radii of the solvent and solute during the dissolution of alumina into the zirconia lattice.The sintering kinetics were proposed to be enhanced by the presence of substantial defects,which consequently favored the low-temperature sintering of the alumina-doped zirconia ceramics.

Synthesis, Structure, and Magnetic Properties of a New Selenite Compound CdNi(SeO3)2(H2O)2

A new selenite compound CdNi(SeO3)2(H2O)2 has been obtained by a conventional hydrothermal method.This compound crystallizes in monoclinic system of space group C2/c,which exhibits a layer structure built by NiO6 octahedra and SeO3 trigonal pyramids running along the a-axis.The layers show a unique eight-rings hole network.The compound is stable at room temperature while the loss of H2O molecules happens with heating above 523 K.Magnetic measurements indicate that CdNi(SeO3)2(H2O)2 is an antiferromagnet and possesses an antiferromagnetic ordering at TN=15 K.