Developments in Ceramic Materials Research

Coloured ZrSiO4 Ceramic Pigments 273
XPS Analyses
The first aspect which can be considered in commenting XPS results is the change in
XPS spectra of the V 2p3/2 region, depending on the final colour of the pigment. The green or
yellow powders show the presence of two V components (Figure 9a), while the blue samples
show a single component (Figure 9b). The components can be attributed to: i) 517.2 eV V 5+ ,
ii) 516.5 eV V 4+ and iii) 515.6 eV V 3+ . A further aspect concerns the trend of the V/Zr atomic
ratios reported in Table 1. In the case of samples obtained in the absence of mineralizers the
observed V/Zr ratio is 0.2 and 0.3 at 800 and 1000°C respectively; these values, when
compared with the V/Zr ratio of 0.1 adopted in the synthesis, indicate the occurrence of a
certain degree of surface segregation of V with respect to the bulk. Also in the presence of Li
salts the V/Zr ratio is around 0.2-0.3 and goes up to 0.6 in the case of LiF at 1000°C. In the
case, instead, of the addition of the other mineralizers, the V/Zr ratio drops to values around
0.1 matching the stoichiometric value. These observations suggest that the addition of the
mineralizers, all except Li salts, promote the incorporation of the V ion into the zircon lattice.
In the case instead of Li salts, Li and V compete for the same positions in the lattice due to
the close proximity of their sizes. Li salts therefore, on one side promote the formation of the
zircon lattice but, on the other side, “throw out” V from the lattice positions thus making the
colour of the pigment less intense.
The Si/Zr atomic ratios range for all the samples around the stoichiometric value of 1.0
except for samples V0.1800 and V0.1NaCl.800 in which the fraction of zircon is not very high
and apparently ZrO2 is segregated at the surface.
Figure 9. XPS V 2p 3/2 region of a) V 0.10 and b) V 0.10NaF calcined at 800°C.