Geoscience Reference
In-Depth Information
Table 7.27 Morphology of Yttrium Orthovanadates
Composition Growth Temperature
(
C)
pH Range
Common Faces Growth
Rate
γ
(110)
.
γ
(010)
Nd:YVO
4
240
0.05 to 0.10
(001) (010)
(110)
γ
(100)
.
γ
(010)
Nd:YVO4
240
2
0.03 to
0.15
(001) (100)
(010)
110
001
001
110
010
110
Nd: YVO
4
pH = 0.08
Nd: YVO
4
pH = -0.08
Figure 7.78 Morphology of rare earth vanadates
[321]
.
through spontaneous nucleation provided by temperature oscillations were
4.2
2.0 mm
3
in about 8 days of experimental duration. Simple rare earth
vanadate crystals were obtained when the pH was kept low (
4.2
3
3
4.0), and Y(OH)
3
and
,
YVO
4
nH
2
O crystallized when pH
4.0. Well-developed platelets were obtained
.
in the pH range
0.15 (see morphology shown in
Figure 7.78
). In situ
growth of the desired morphology under moderate hydrothermal conditions has
shown in general that yttrium orthovanadate crystals have a strong tendency to flat-
tening. The authors have shown that some rare earth orthovanadates obtained by the
flux method, bearing Pr, Eu, and Tm, are almost isometric. A study of the growth
rate of the rare earth vanadate crystals was attempted and
Figure 7.79
shows the
dependence of growth rate on the pH of the growth media. Higher growth rate was
obtained in the pH range
0.03 to
2
2
0.08 to 0.08, in which the crystals grow thicker and the
optical quality suffers. It has been reported earlier that the rare earth vanadates
belonging to the zircon type show a tendency for banding/zoning, particularly on the
(001) face
[337]
. The yttrium orthovanadate crystals generally show dark brown to
light brown colors with a change in the dopant level. The darker colors appear when
the crystals grow thicker and molar ratio is not maintained properly because the
growth depends on the control of oxygen activity and surplus V
2
O
5
. A small quan-
tity of hydrogen peroxide was added in order to create oxygen rich atmosphere and
that in turn improved the quality of the crystals. They became honey-yellow in color,
uniform throughout, and the transparency also increased. The hydrothermally grown
crystals do not show zoning or banding, unlike the rare earth orthovanadates
obtained by other techniques.
2
