ZrO 2 . As a consequence on Al 2 O 3 , the stronger metal–CO interaction weakens the
C–O bond and leads to hydrocarbon formation; on ZrO 2 , the weaker interaction
cannot lead to dissociation of the C–O bond and oxygenated products are formed.
5.16 The Case of Phosphate Glasses Containing
Ruthenium and Titanium Ions
Oxide glasses containing transition metals have attracted interest for a long time due
to their behavior as disordered semiconductors [13]. Their semiconductive properties are interpreted as being due to the presence of mixed valence transition metal
ions. According to Austin and Mott, the electronic behavior of these systems could
be well described in terms of thermally assisted hopping of electrons; however, this
model is able to give only qualitative description of the conduction processes. It
seems mandatory the detection of the different oxidation states of the transition
metal ions dispersed in the glasses.
5.17 Discussion of the Case
Glasses containing TiO 2 as well as RuO 2 were obtained from mixtures of Na 2 TiO 3 ,
sodium metaphosphate, and orthophosphoric acid melted at 1260 °C. Reduced
titanium and ruthenium centers, present near the major amount of oxidized ones,
have been detected by electron spin resonance investigation, and the g tensor values
are in accordance with Ru
3+ and Ti
3+ species (Fig. 5.14).
The trends in the amount of reduced Ti and Ru centers (Ti
3+ , Ru
3+ ) allow to
acknowledge the distribution of the transition metal ions in samples having different
concentrations and to design the samples with the desired electric characteristics.
5.18 Chemical Message
The presence of two different oxidation states for the doping transition metal ions is
a prerequisite to control the electric conductivity, based on the Austin and Mott
model. The reported investigation allows to detect the magnetic dilution of the
paramagnetic centers and to predict the conditions suitable for the hopping
mechanism.
5.15 Chemical Message
103
C–O bond and leads to hydrocarbon formation; on ZrO 2 , the weaker interaction
cannot lead to dissociation of the C–O bond and oxygenated products are formed.
5.16 The Case of Phosphate Glasses Containing
Ruthenium and Titanium Ions
Oxide glasses containing transition metals have attracted interest for a long time due
to their behavior as disordered semiconductors [13]. Their semiconductive properties are interpreted as being due to the presence of mixed valence transition metal
ions. According to Austin and Mott, the electronic behavior of these systems could
be well described in terms of thermally assisted hopping of electrons; however, this
model is able to give only qualitative description of the conduction processes. It
seems mandatory the detection of the different oxidation states of the transition
metal ions dispersed in the glasses.
5.17 Discussion of the Case
Glasses containing TiO 2 as well as RuO 2 were obtained from mixtures of Na 2 TiO 3 ,
sodium metaphosphate, and orthophosphoric acid melted at 1260 °C. Reduced
titanium and ruthenium centers, present near the major amount of oxidized ones,
have been detected by electron spin resonance investigation, and the g tensor values
are in accordance with Ru
3+ and Ti
3+ species (Fig. 5.14).
The trends in the amount of reduced Ti and Ru centers (Ti
3+ , Ru
3+ ) allow to
acknowledge the distribution of the transition metal ions in samples having different
concentrations and to design the samples with the desired electric characteristics.
5.18 Chemical Message
The presence of two different oxidation states for the doping transition metal ions is
a prerequisite to control the electric conductivity, based on the Austin and Mott
model. The reported investigation allows to detect the magnetic dilution of the
paramagnetic centers and to predict the conditions suitable for the hopping
mechanism.
5.15 Chemical Message
103