U. Martin et al., NEUTRON POWDER INVESTIGATION OF TETRAGONAL AND CUBIC STABILIZED ZIRCONIA, TZP AND CSZ, AT TEMPERATURES UP TO 1400-K, Acta crystallographica. Section B, Structural science, 49, 1993, pp. 403-413
A comparative study of tetragonal (Y-TZP, 3 mol% Y2O3) and cubic (CSZ,
15 mol% CaO) zirconia Powder samples was carried out to learn about a
Possible structural origin of the superior ionic conductivity of TZP
at low temperatures. Structure refinements including anharmonic temper
ature factors and oxygen occupancies as well as a qualitative analysis
of the diffuse background revealed large differences especially of th
e anisotropy of thermal motion and the underlying disorder in both sam
les. Diffusion pathways are restricted to layers in TZP, in contrast
with a three-dimensional behaviour in CSZ. The structural arrangement
of the tetragonal phase is slightly more favourable for conduction pro
cesses. More importantly, the higher concentration of oxygen vacancies
in CSZ is less operative due to an immobilization of these charge car
riers by coherent and incoherent microclustering at low temperatures,
whereas the smaller number of vacancies in TZP is fully available for
transport processes. At higher temperatures - as CSZ approaches the tr
ue thermodynamic stability field of the cubic structure - the stabiliz
ing function of the microclusters decreases, the clusters dissolve and
the ionic conductivity in CSZ becomes superior to that in TZP. No suc
h processes take place in TZP. The behaviour in powdered samples diffe
rs from that in single crystals.