X-ray photoelectron spectra of RNa2O . B2O3 . KSiO2 (R = 0.2 to 5.0, K = 0.
5 to 6.0) glasses were measured by a monochromatised Al-Ka XPS instrument.
Chemical shifts of the core-level photoelectron spectra of the glass consti
tuent ions were investigated. Peaks at the higher and lower energy sides of
an Ols signal were ascribed to bridging oxide (BO) and non-bridging oxide
(NBO) components, respectively. The BO component could not be separated int
o the oxide ions with different environment such as Si-O-Si, B-O-Si and B-O
-B. Na1s signal could not be separated into two components of Na+ ions asso
ciated with [BO4/2](-) tetrahedron and NBO. For the small K values (=0.5 an
d 1.0), the NBO fractions measured by XPS agreed very well with the structu
ral model proposed by Dell et al. [J. Non-Cryst. Soilds 58 (1983) 1], where
NBO did not appear until R = 0.5 regardless of K values. With increasing K
, however, the dependence of the NBO fraction upon R gradually came to disa
gree with the Dell model. At smaller R values than Rv = 0.5 +K/16, the NBO
component already appeared to a considerable extent and the discrepancy bet
ween the XPS results and the Dell model became more significant with increa
sing K. This fact meant that additional sodium oxides were shared proportio
nally between silicate and borate networks even at the small R when K was l
arger than 2. A new sharing model was proposed on the basis of an acid-base
concept. (C) 2001 Elsevier Science B.V. All rights reserved.