L1₂- and L1₀-like cation-ordered structures in ZrO₂–Y₂O₃ ceramics

Abstract

Y 0.25 Zr 0.75 O 2-x and Y 0.5 Zr 0.5 O 2-y phases, with L1 2 -and L1 0 -like cation-ordered structures, respectively, have been found in ZrO 2 -Y 2 O 3 ceramics in both the sintered and annealed states. High-resolution electron microscopy, energy-dispersive x-ray spectroscopy and computer simulation have been used to reveal the presence of the phases. The formation of Y 0.25 Zr 0.75 O 2-x and Y 0.5 Zr 0.5 O 2-y phases was initiated during the sintering procedure and developed with the increase in annealing temperature and time. Segregation of yttrium, which was prevalent in different regions even within one grain, induced the formation of Y 0.25 Zr 0.75 O 2-x and Y 0.5 Zr 0.5 O 2-y phases.

Characterization of Diffuse Scattering in Yttria-Stabilized Zirconia by Electron Diffraction and High-Resolution Transmission Electron Microscopy

“…Similar SAED patterns have been found for samples with composition 8, ,,− 10, ,,,− and 12 mol % Y 2 O 3 , rapidly cooled from high temperatures. Zhou et al suggest that the appearance of reflections at G F ± (112)* is caused by small displacements of the oxygen ions from their ideal positions along the [001] f , [100] f , and [010] f directions, but the symmetry of the phase remains cubic (they name it c′ phase).…”

“…McClellan et al propose a distortion of the oxygen sublattice from the ideal fluorite structure by displacement along the [111] f directions, giving also a cubic symmetry. Rao et al indicate the formation of Y 0.25 Zr 0.75 O 2− x (L1 2 ) and Y 0.5 Zr 0.5 O 2− y (L1 0 ) cation-ordered structures, in some regions of the crystals due to yttrium segregation, which originate the superlattice reflections at G F ± (001)* and G F ± (110)*, but Kondoh et al have related these extra reflections to some kind of periodic and anisotropic lattice distortions. , Other authors have explained their results on the basis of the diffusionless cubic to metastable tetragonal phase (t′) transformation accompanied by the formation of three t′ variants with the c t′ axis being parallel to each of the three original [001] f directions. ,, Butz et al have recently suggested the formation of tetragonal and monoclinic (m′) regions within the cubic grains of 8YSZ …”

Enthalpy of formation of cubic yttria-stabilized hafnia

“…It is reasonable to expect extensive short range order in the HfO 2 -YO 1.5 system. While the existence of short range order in the ZrO 2 -YO 1.5 system has been verified by direct observation, [26][27][28][29] the existence of short range order in the HfO 2 -YO 1.5 system has been inferred from electrical conductivity measurements. 7,30 In these studies, a maximum in conductivity is observed with doping level, and, as in the ZrO 2 -YO 1.5 system, this is ascribed to defect ordering.…”

Oxygen vacancy ordering induced displacements of cations in yttria-stabilized zirconia

“…The presence of the {010}-type forbidden reflections of the FCC lattice in the 2D lattice region suggests that the cubic fluorite structure undergoes locally disorder → order transition, for which Zr and Y atoms occupy the regular lattice sites of the unit cell of the L10 ordered structure. 16,32 In order to reveal the atomic structure of the regions having the superlattice reflections, HAADF imaging was performed using aberration-corrected STEM. Fig.…”

“…13 The presence of oxygen vacancies causes relaxation of ions away from their regular fluorite lattice positions. [14][15][16] The nature of the defect-induced atomic displacements has been a controversial topic for some time. The directions of <110> 17 or <111> 18-20 were proposed for the displacements of cations, and the direction of <100>, 15,19-21 <111>, 20,[22][23][24] or both 15,18 were suggested for the relaxations of anions.…”