Jp. Goff et al., Defect structure of yttria-stabilized zirconia and its influence on the ionic conductivity at elevated temperatures, PHYS REV B, 59(22), 1999, pp. 14202-14219
The defect structure of cubic fluorite structured yttria-stabilized zirconi
a (ZrO2)(1-x)(Y2O3)(x) has been investigated over the composition range 0.1
00(3)less than or equal to x less than or equal to 0.241 (10) and temperatu
res T(K) up to 2780(10) K, using single-crystal specimens. Analysis of neut
ron and x-ray diffraction data, including both Bragg and coherent diffuse s
cattering components, has identified three principal types of defects withi
n the fluorite lattice. At low yttria concentrations (x<similar to 0.15) th
ere are regions of the crystal similar to 20 Angstrom in size which contain
relatively few oxygen vacancies, causing the lattice to undergo a slight t
etragonal distortion of the type observed in the tetragonal phase of (ZrO2)
(1-x)(Y2O3)(x) at x < similar to 0.09. The oxygen vacancies are preferentia
lly arranged in pairs on nearest-neighbor anion sites in the (111) fluorite
directions, with a cation located between them and extensive relaxations o
f the surrounding nearest-neighbor cations and anions. As the yttria conten
t increases, these (111) vacancy Fairs pack together in (112) directions to
form aggregates, whose short-range defect structure resembles the long-ran
ge crystal structure of the ordered compound Zr3Y4O12 and other anion-defic
ient fluorite-related systems. The aggregates are typically similar to 15 A
ngstrom in diameter, though both their size and number density increase sli
ghtly with x. On increasing the temperature, these aggregates remain stable
up to close to the melting point. There is also an increasing number of si
ngle vacancies and (111) vacancy pairs (with surrounding relaxation fields)
as x increases, and these isolated clusters become mobile at T>similar to
1000 K and give rise to the high ionic conductivity of the material. In lig
ht of these observations, we propose that the anomalous decrease in the ion
ic conductivity with increasing x is a consequence of the decreasing mobili
ty of the isolated defects, possibly due to blockage by the increasing numb
er of static aggregates. [S0163-1829(99)05621-0].