Defect structure of zirconia (Zr0.85Ca0.15O1.85) at 290 and 1550 K

Abstract

A quantitative interpretation of diffuse neutron scattering has yielded an accurate description of the defect structure of CaO stabilized zirconia (CSZ) at 290 and 1550 K. The defect structure is based on the correlated distribution of two different types of microdomains within the disordered structure. The first microdomain is built around a single oxygen vacancy with relaxed neighboring ions. The first neighbors are relaxed along (100), second neighbors are relaxed along (111) and (110). The second microdomain is built around a pair of oxygen vacancies separated by a31/2/2 along (lid with a Ca ion in between. There is no qualitative change at high temperatures. The correlation length, however, decreases considerably.

Neutron and X-ray diffuse scattering of calcium-stabilized zirconia

“…The only difference between these models is the occupation of the position marked with M in the two microdomain types. Model 1 is exactly the model used by Neder, Frey & Schulz (1990b). For all models a simultaneous refinement of neutron and X-ray data was performed.…”

“…The neutron diffraction data used in this study were collected on the neutron spectrometer MAN II at the FRM research reactor in Garching, Munich, Germany, by Neder, Frey & Schulz (1990b), i.e. the zeroth and second layer of the [ll0]-zone measured in the integral mode of the spectrometer at wavelength 1.093 A.…”

“…Ho (1982) suggests that the zirconium ions occupy seven-coordinated cation sites in the locally distorted fluorite-type structure. Neder, Frey & Schulz (1990b) analysed the neutron diffuse scattering of CSZ doped with 15 mol% CaO by a model of a correlated distribution of microdomains* within the matrix of cubic zirconia. Neder, Frey & Schulz (1990b) introduced two types of microdomains, one based on a single oxygen vacancy with relaxed neighbouring ions and a second based on a pair of oxygen vacancies separated by 3t/2/2a along <ll 1>.…”

“…© 1996 International Union of Crystallography lh'inted in Great Britain -all rights reserved is still under debate in the literature (see references in Neder, Frey & Schulz, 1990b;, particularly the question which cation is the next neighbour of an oxygen vacancy. Dwivedi & Cormack (1990) suggest the calcium ion to be the next-nearest neighbour of the vacancy based on energy calculations.…”

“…Welberry, Butler, Thompson & Withers (1993), however, attacked the single-vacancy microdomain as being not chemically plausible. Therefore, we reinvestigated this problem by neutron and X-ray data, since Neder, Frey & Schulz (1990b) could not fully exclude the existence of microdomains with only zirconium as next neighbours to the oxygen vacancy from their calculations based on neutron scattering data exclusively. The combined refinement of neutron and X-ray data should give a more reliable insight into the defect structure of stabilized zirconia.…”