Geoscience Reference
In-Depth Information
However, the crystals exhibit simple twinning and pseudotriclinic symmetry.
Figure 8.13
represents the schematic diagrams of NaLa(WO
4
)
2
crystals.
Figures 8.14
and 8.15
show the variation in the growth rate and morphology of NaLa(WO
4
)
2
crys-
tals with the pH of the medium and internal pressure, respectively. Good quality crys-
tals were obtained in the pH range 8.4
8.8.
Figure 8.16
shows the representative
photographs of the alkali rare earth tungstates obtained by Byrappa and Jain
[53]
.The
size of the crystals increases with an increase in the pH of the medium, but the quality
of the crystals becomes poor and beyond pH 11.5, NaLa(WO
4
)
2
does not crystallize.
The growth rate of NaLa(WO
4
)
2
crystals was found to increase with an increase in
pressure, and good quality crystals were obtained at about 120 bar. The twinning is
011
001
011
010
010
110
110
110
010
111
Pseudotriclinic
(a)
(b)
(c)
001
110
100
-
110
110
(d)
(e)
Figure 8.13 Schematic diagrams of NaLa(WO
4
)
2
crystals
[53]
.
