Synthesis and sintering of zirconia-erbia tetragonal solid solutions

The preparation of zirconia/erbia tetragonal solid solution was attempted by sintering of powders produced by coprecipitation, Calcined powders were attrition milled and green bodies densified to materials having grain size of a nanometer scale. Fired materials reached high density after firing at any temperatures above 1850 degrees C for times of 1 h or more; they had a tetragonal structure, provided that the erbia content exceeded 1.5 mol%. Materials containing 1.5 mol% erbia consisted of both monoclinic and tetragonal phases, when the firing conditions were selected at the lowest temperature for densification (1 h at 1350 degrees C). In all other cases, only the monoclinic structure could be detected, Materials containing 2, 2.5 and 3 mol% erbia had tetragonal symmetry. In particular, tetragonal solid solutions contaning 2 mol% Er2O3 mantained such structure until their grain size did not exceed 1 mu m, at larger grain sizes they transformed to monoclinic. The tetragonal lattice parameters were measured by X-ray diffraction analysis in all the tetragonal materials and they agreed with those previously reported by other authors. The crystallographic a/c ratio had influence on the grain tranformability: the lower the ratio, the lower the tetragonal/monoclinic transformation ratio.