  Experimental data obtained by Lughi and Clarke [J. Am. Ceram. Soc., 88, 2552
(2005)] are compared to the theory describing disorder effects on optical
phonons. Sharpening and vanishing of the asymmetry of the Raman lines after
annealing are attributed to a decrease in short-range disorder. The parameters
of disorder (such as the phonon-defect coupling and the correlation length) are
defined in the comparison.
