Vitreous samples were prepared i
n the (100 -
x)% NaPO
3-
x%
MoO
3 (0
![](/images/e<font color=)
ntities/le.gif">
x ![](/images/e<font color=)
ntities/le.gif"> 70) glass-formi
ng system bya
modified melt method that allowed good optical quality samples to be obtai
ned. The structural evolutio
n ofthe vitreous
network was
monitored as a fu
nctio
n of compositio
n by differe
ntial sca
nni
ng calorimetry (DSC),Fourier tra
nsform i
nfrared spectroscopy (FT-IR), Rama
n scatteri
ng, a
nd solid-state
nuclear mag
netic reso
na
nce(NMR) for
31P,
23Na, a
nd
95Mo
nuclei. Additio
n of MoO
3 to the NaPO
3 glass melt leads to a pro
nou
ncedi
ncrease i
n the glass tra
nsitio
n temperatures up to
x = 45, suggesti
ng a sig
nifica
nt i
ncrease i
n networkco
nnectivity. For this same compositio
n ra
nge, vibratio
nal spectra suggest that the Mo
6+ io
ns are bo
nded tosome
no
nbridgi
ng oxyge
n atoms (Mo-O
- or Mo=O bo
nded species). Mo-O-Mo bo
nd formatio
n occurso
nly at MoO
3 co
nte
nts exceedi
ng
x = 45.
31P magic-a
ngle spi
nni
ng (MAS) NMR spectra, supported by two-dime
nsio
nal
J-resolved spectroscopy, allow a clear disti
nctio
n betwee
n species havi
ng two, o
ne, a
nd zeroP-O-P li
nkages. These sites are de
noted as Q
(2)2Mo, Q
(2)1Mo, a
nd Q
(2)0Mo, respectively. For
x < 0.45, thepopulatio
ns of these sites ca
n be described alo
ng the li
nes of a bi
nary
model, accordi
ng to which each u
nitof MoO
3 co
nverts two Q
(2)nMo sites i
nto two Q
(2)(n+1)Mo sites (
n = 0, 1). This structural
model is co
nsiste
ntwith the prese
nce of tetrahedral Mo(=O)
2(O
1/2)
2 e
nviro
nme
nts. I
ndeed,
95Mo NMR data suggest that themajority of the
molybde
num species are four-coordi
nated. However, the prese
nce of additio
nal six-coordi
nate
molybde
num i
n the MAS NMR spectra i
ndicates that the structure of these glasses may be
more complicateda
nd may additio
nally i
nvolve shari
ng of
network
modifier oxide betwee
n the
network formers phosphorusa
nd
molybde
num. This latter hypothesis is further supported by
23Na{
31P} rotatio
nal echo double reso
na
nce(REDOR) data, which clearly reveal that the mag
netic dipole-dipole i
nteractio
ns betwee
n 31P a
nd
23Na arei
ncreasi
ngly dimi
nished with i
ncreasi
ng
molybde
num co
nte
nt. The partial tra
nsfer of
modifier from thephosphate to the
molybdate
network former implies a partial repolymerizatio
n of the phosphate species, resulti
ngi
n the formatio
n of Q
(3)nMo species a
nd accou
nti
ng for the observed i
ncrease i
n the glass tra
nsitio
n temperaturewith i
ncreasi
ng MoO
3 co
nte
nt that is observed i
n the compositio
n ra
nge 0
![](/images/e<font color=)
ntities/le.gif">
x ![](/images/e<font color=)
ntities/le.gif"> 45. Glasses with MoO
3co
nte
nts beyo
nd
x = 45 show decreased thermal a
nd crystallizatio
n stability. Their structure is characterizedby isolated phosphate species [
most likely of the P(OMo)
4 type] a
nd
molybde
num oxide clusters with a largeexte
nt of Mo-O-Mo co
nnectivity.