Inelastic neutron scattering from cubic stabilised zirconia
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Date
1994-02-09
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Australian and New Zealand Institutes of Physics
Abstract
Phonon dispersion curves have been measured for three cubic stabilised zirconias (CSZ) with varying amounts of oxygen vacancies (Zr(Y)O1.193, Zr(Ca)O1.875, Zr(Y)O1.805), using a triple axis spectrometer. We have been able to observe transverse (TA) and longitudinal acoustic (LA) branches for these crystals. However in agreement with previous work, and despite an exhaustive search in (Q,ω) space, optic modes were not observed 1. The behaviour of the LA and TA branches is atypical, in that phonons become increasingly broader, and weaker close to the Brillouin zone boundary. This is particularly the case for the [ζζ0] direction, where the TA2 branch disappears beyond ζ=0.45. This atypical behaviour has been speculated to be caused by to the defect fluorite structure of CSZ. Recently a reliable model of the static structure has been determined 2 and has been used here to explain the observed inelastic neutron scattering observations. To understand the effect of the defect structure of CSZ to the observed neutron measurements, lattice dynamical calculations have been carried out on the basis of the static structure. These calculations show that the stability of CSZ is particular sensitive to the [100] interactions between oxygen atoms. They show that either relatively small variations in the force constants for this interaction, associated with variations of the 0-0 bondlengths in the defect structure, or the incorporation of vacancies into the structure can render the [(ζζ0] TA2 mode mutable. This is in agreement with the experimental results which shows that this mode disappears rapidly. These calculations also show a general broadening of all phonon branches. This makes the measurer lent of the optic phonon particularly difficult. It is found therefore that the static defect model of CSZ is consistent with the inelastic neutron scattering measurements.
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Keywords
Alkaline earth metal compounds, Chalcogenides, Crystal lattices, Diffraction, Mathematical models, Nonmetals, Oxygen compounds, Quasi particles, Scattering, Transition element compounds
Citation
Argyriou, D. N., Elcombe, M. M. (1994). Inelastic neutron scattering from cubic stabilised zirconia. Poster presented to the 18th Annual Condensed Matter Physics Meeting, Charles Sturt University, Wagga Wagga, NSW, 9-11 February 1994.