T. Hattori et M. Ishigame, ELECTRONIC BAND STRUCTURES OF AND IONIC-CONDUCTION IN BETA-ALUMINA-TYPE SUPERIONIC CONDUCTORS, Solid state ionics, 109(3-4), 1998, pp. 197-205
The electronic band structures of beta-alumina-type superionic conduct
ors (SIC) are proposed and discussed using experimental results for th
e reflection and absorption spectra in the ultraviolet and vacuum-ultr
aviolet regions and photoemission spectra. The measurements were perfo
rmed using beam Lines with synchrotron radiation. The valence bands of
all beta-alumina-type SIC are constructed from the 2p orbital of oxyg
en (O 2p). In the case of alkali beta ''-aluminas, the lowest conducti
on band is due to the s orbitals of alkali ions. It is concluded from
this result that all conduction ions are not perfectly free, but const
ruct bonds, giving rise to an ordered structure existing in a limited
region. On the other hand, in the case of alkali beta-aluminas, this i
s due to the 3s orbital of aluminum. The low lying exciton bands due t
o the orbitals of Ag ions and due to the orbitals of Tl ions are obser
ved in Ag beta- and Ag beta ''-aluminas, and in Tl beta- and Tl beta '
'-aluminas, respectively. In these cases, there are also ordered regio
ns in the conduction plane or slab. It is therefore suggested that an
ordered structure of the conduction plane or slab should be considered
in order to understand the ionic conduction in beta-alumina-type SIG.
(C) 1998 Elsevier Science B.V. All rights reserved.