It was recalled that, during a previous study of this material, an unexpected Na metal deposition phenomenon had been observed; especially in the case of spot irradiation with an electron beam. It was suggested that the metal deposition was due to an electrostatic interaction between mobile Na ions in the conductor, and the irradiating electrons, leading to Na+ ion reduction. Further study indicated that the Na metal deposition mechanism reflected the occurrence of ionic migration processes in the conductor. That is, the ionic migration process dominated the observed Na accumulation rate during the reduction process. The ionic mobility of cation conductors could then be estimated from the accumulation of deposited metal, due to reduction of the carrier by the anionic electron beam. The use of this method revealed a partial structural change as a result of homogeneous doping. This mainly affected the ionic mobility and was expected to alter the Na deposition rate.

Y.Saito, M.Nakagawa, M.Yamada, Y.Miyajima, Y.Yamamoto: Journal of Materials Science Letters, 1996, 15[10], 898-901