start-ver=1.4
cd-journal=joma
no-vol=68
cd-vols=
no-issue=24
article-no=
start-page=5103
end-page=5111
dt-received=
dt-revised=
dt-accepted=
dt-pub-year=2004
dt-pub=20041215
dt-online=
en-article=
kn-article=
en-subject=
kn-subject=
en-title=
kn-title=A theoretical interpretation of the chemical shift of Si-29 NMR peaks in alkali borosilicate glasses
en-subtitle=
kn-subtitle=
en-abstract=
kn-abstract=In Si-29-NMR, it has so far been accepted that the chemical shifts of Q(n) Species (SiO4 units containing n bridging oxygens) were equivalent between alkali borosilicate, and boron-free alkali silicate classes. In the sodium borosilicate glasses with low sodium content. however. a contradiction was confirmed in the estimation of alkali distributions B-11 NMR suggested that Na ions were entirely distributed to berate groups to form BO4 units, whereas a -90 ppm component Was also observed in Si-29-NMR spectra, which has been attributed to Q(3) species associated with a nonbridging oxygen (NBO). Then. cluster molecular orbital calculations were performed to interpret the -90 ppm component in the borosilicate, glasses. It Was found that a silicon atom which had two tetrahedral borons (B4) as its second nearest neighbors was similar in atomic charge and Si2p energy to the Q(3) species in boron-free alkali silicates. Unequal distribution of electrons in Si-O-B4 bridging bonds was also found. where much electrons Were localized oil the Si-O bonds. It was finally concluded that the Si-O-B4 bridges with narrow bond angle were responsible for the -90 ppm Si-29 component in the borosilicate glasses. There still remained another interpretation: the Q(3) species were actually present in the glasses. and NBOs in the Q(3) species were derived from the tricluster groups. such as (O3Si)O(BO3)(2). In the classes With low sodium content. however. it was concluded that the tricluster groups were not so abundant to contribute to the -90 ppm component.
en-copyright=
kn-copyright=

en-aut-name=NanbaTokuro
en-aut-sei=Nanba
en-aut-mei=Tokuro
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=1
ORCID=

en-aut-name=NishimuraMitsunori
en-aut-sei=Nishimura
en-aut-mei=Mitsunori
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=2
ORCID=

en-aut-name=MiuraYoshinari
en-aut-sei=Miura
en-aut-mei=Yoshinari
kn-aut-name=
kn-aut-sei=
kn-aut-mei=
aut-affil-num=3
ORCID=

affil-num=1
en-affil=
kn-affil=Okayama University

affil-num=2
en-affil=
kn-affil=Okayama University

affil-num=3
en-affil=
kn-affil=Okayama University
en-keyword=short-range order
kn-keyword=short-range order
en-keyword=nuclear-magnetic-resonance
kn-keyword=nuclear-magnetic-resonance
en-keyword=mas-nmr
kn-keyword=mas-nmr
en-keyword=structural
kn-keyword=structural
en-keyword=groups
kn-keyword=groups
en-keyword=oxygen sites
kn-keyword=oxygen sites
en-keyword=ab-initio
kn-keyword=ab-initio
en-keyword=o-17 nmr
kn-keyword=o-17 nmr
en-keyword=b-11
kn-keyword=b-11
en-keyword=na20-b2-3-s1-2
kn-keyword=na20-b2-3-s1-2
en-keyword=spectroscopy
kn-keyword=spectroscopy
END